/** @file @brief Semi-join subquery optimizations code */ #ifdef USE_PRAGMA_IMPLEMENTATION #pragma implementation // gcc: Class implementation #endif #include "sql_select.h" #include "opt_subselect.h" #include "sql_test.h" #include /* This file contains optimizations for semi-join subqueries. Contents -------- 1. What is a semi-join subquery 2. General idea about semi-join execution 2.1 Correlated vs uncorrelated semi-joins 2.2 Mergeable vs non-mergeable semi-joins 3. Code-level view of semi-join processing 3.1 Conversion 3.1.1 Merged semi-join TABLE_LIST object 3.1.2 Non-merged semi-join data structure 3.2 Semi-joins and query optimization 3.2.1 Non-merged semi-joins and join optimization 3.2.2 Merged semi-joins and join optimization 3.3 Semi-joins and query execution 1. What is a semi-join subquery ------------------------------- We use this definition of semi-join: outer_tbl SEMI JOIN inner_tbl ON cond = {set of outer_tbl.row such that exist inner_tbl.row, for which cond(outer_tbl.row,inner_tbl.row) is satisfied} That is, semi-join operation is similar to inner join operation, with exception that we don't care how many matches a row from outer_tbl has in inner_tbl. In SQL terms: a semi-join subquery is an IN subquery that is an AND-part of the WHERE/ON clause. 2. General idea about semi-join execution ----------------------------------------- We can execute semi-join in a way similar to inner join, with exception that we need to somehow ensure that we do not generate record combinations that differ only in rows of inner tables. There is a number of different ways to achieve this property, implemented by a number of semi-join execution strategies. Some strategies can handle any semi-joins, other can be applied only to semi-joins that have certain properties that are described below: 2.1 Correlated vs uncorrelated semi-joins ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Uncorrelated semi-joins are special in the respect that they allow to - execute the subquery (possible as it's uncorrelated) - somehow make sure that generated set does not have duplicates - perform an inner join with outer tables. or, rephrasing in SQL form: SELECT ... FROM ot WHERE ot.col IN (SELECT it.col FROM it WHERE uncorr_cond) -> SELECT ... FROM ot JOIN (SELECT DISTINCT it.col FROM it WHERE uncorr_cond) 2.2 Mergeable vs non-mergeable semi-joins ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Semi-join operation has some degree of commutability with inner join operation: we can join subquery's tables with ouside table(s) and eliminate duplicate record combination after that: ot1 JOIN ot2 SEMI_JOIN{it1,it2} (it1 JOIN it2) ON sjcond(ot2,it*) -> | +-------------------------------+ v ot1 SEMI_JOIN{it1,it2} (it1 JOIN it2 JOIN ot2) ON sjcond(ot2,it*) In order for this to work, subquery's top-level operation must be join, and grouping or ordering with limit (grouping or ordering with limit are not commutative with duplicate removal). In other words, the conversion is possible when the subquery doesn't have GROUP BY clause, any aggregate functions*, or ORDER BY ... LIMIT clause. Definitions: - Subquery whose top-level operation is a join is called *mergeable semi-join* - All other kinds of semi-join subqueries are considered non-mergeable. *- this requirement is actually too strong, but its exceptions are too complicated to be considered here. 3. Code-level view of semi-join processing ------------------------------------------ 3.1 Conversion and pre-optimization data structures --------------------------------------------------- * When doing JOIN::prepare for the subquery, we detect that it can be converted into a semi-join and register it in parent_join->sj_subselects * At the start of parent_join->optimize(), the predicate is converted into a semi-join node. A semi-join node is a TABLE_LIST object that is linked somewhere in parent_join->join_list (either it is just present there, or it is a descendant of some of its members). There are two kinds of semi-joins: - Merged semi-joins - Non-merged semi-joins 3.1.1 Merged semi-join TABLE_LIST object ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Merged semi-join object is a TABLE_LIST that contains a sub-join of subquery tables and the semi-join ON expression (in this respect it is very similar to nested outer join representation) Merged semi-join represents this SQL: ... SEMI JOIN (inner_tbl1 JOIN ... JOIN inner_tbl_n) ON sj_on_expr Semi-join objects of this kind have TABLE_LIST::sj_subq_pred set. 3.1.2 Non-merged semi-join data structure ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Non-merged semi-join object is a leaf TABLE_LIST object that has a subquery that produces rows. It is similar to a base table and represents this SQL: ... SEMI_JOIN (SELECT non_mergeable_select) ON sj_on_expr Subquery items that were converted into semi-joins are removed from the WHERE clause. (They do remain in PS-saved WHERE clause, and they replace themselves with Item_int(1) on subsequent re-executions). 3.2 Semi-joins and join optimization ------------------------------------ 3.2.1 Non-merged semi-joins and join optimization ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ For join optimization purposes, non-merged semi-join nests are similar to base tables - they've got one JOIN_TAB, which can be accessed with one of two methods: - full table scan (representing SJ-Materialization-Scan strategy) - eq_ref-like table lookup (representing SJ-Materialization-Lookup) Unlike regular base tables, non-merged semi-joins have: - non-zero JOIN_TAB::startup_cost, and - join_tab->table->is_filled_at_execution()==TRUE, which means one cannot do const table detection or range analysis or other table data- dependent inferences // instead, get_delayed_table_estimates() runs optimization on the nest so that // we get an idea about temptable size 3.2.2 Merged semi-joins and join optimization ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ - optimize_semijoin_nests() does pre-optimization - during join optimization, the join has one JOIN_TAB (or is it POSITION?) array, and suffix-based detection is used, see advance_sj_state() - after join optimization is done, get_best_combination() switches the data-structure to prefix-based, multiple JOIN_TAB ranges format. 3.3 Semi-joins and query execution ---------------------------------- * Join executor has hooks for all semi-join strategies. TODO elaborate. */ static bool subquery_types_allow_materialization(Item_in_subselect *in_subs); static bool replace_where_subcondition(JOIN *join, Item **expr, Item *old_cond, Item *new_cond, bool do_fix_fields); static int subq_sj_candidate_cmp(Item_in_subselect* el1, Item_in_subselect* el2, void *arg); static bool convert_subq_to_sj(JOIN *parent_join, Item_in_subselect *subq_pred); static bool convert_subq_to_jtbm(JOIN *parent_join, Item_in_subselect *subq_pred, bool *remove); static TABLE_LIST *alloc_join_nest(THD *thd); static uint get_tmp_table_rec_length(Item **p_list, uint elements); static double get_tmp_table_lookup_cost(THD *thd, double row_count, uint row_size); static double get_tmp_table_write_cost(THD *thd, double row_count, uint row_size); bool find_eq_ref_candidate(TABLE *table, table_map sj_inner_tables); static SJ_MATERIALIZATION_INFO * at_sjmat_pos(const JOIN *join, table_map remaining_tables, const JOIN_TAB *tab, uint idx, bool *loose_scan); void best_access_path(JOIN *join, JOIN_TAB *s, table_map remaining_tables, uint idx, bool disable_jbuf, double record_count, POSITION *pos, POSITION *loose_scan_pos); static Item *create_subq_in_equalities(THD *thd, SJ_MATERIALIZATION_INFO *sjm, Item_in_subselect *subq_pred); static void remove_sj_conds(Item **tree); static bool is_cond_sj_in_equality(Item *item); static bool sj_table_is_included(JOIN *join, JOIN_TAB *join_tab); static Item *remove_additional_cond(Item* conds); static void remove_subq_pushed_predicates(JOIN *join, Item **where); enum_nested_loop_state end_sj_materialize(JOIN *join, JOIN_TAB *join_tab, bool end_of_records); /* Check if Materialization strategy is allowed for given subquery predicate. @param thd Thread handle @param in_subs The subquery predicate @param child_select The select inside predicate (the function will check it is the only one) @return TRUE - Materialization is applicable FALSE - Otherwise */ bool is_materialization_applicable(THD *thd, Item_in_subselect *in_subs, st_select_lex *child_select) { st_select_lex_unit* parent_unit= child_select->master_unit(); /* Check if the subquery predicate can be executed via materialization. The required conditions are: 0. The materialization optimizer switch was set. 1. Subquery is a single SELECT (not a UNION). TODO: this is a limitation that can be fixed 2. Subquery is not a table-less query. In this case there is no point in materializing. 2A The upper query is not a table-less SELECT ... FROM DUAL. We can't do materialization for SELECT .. FROM DUAL because it does not call setup_subquery_materialization(). We could make SELECT ... FROM DUAL call that function but that doesn't seem to be the case that is worth handling. 3. Either the subquery predicate is a top-level predicate, or at least one partial match strategy is enabled. If no partial match strategy is enabled, then materialization cannot be used for non-top-level queries because it cannot handle NULLs correctly. 4. Subquery is non-correlated TODO: This condition is too restrictive (limitation). It can be extended to: (Subquery is non-correlated || Subquery is correlated to any query outer to IN predicate || (Subquery is correlated to the immediate outer query && Subquery !contains {GROUP BY, ORDER BY [LIMIT], aggregate functions}) && subquery predicate is not under "NOT IN")) (*) The subquery must be part of a SELECT statement. The current condition also excludes multi-table update statements. A note about prepared statements: we want the if-branch to be taken on PREPARE and each EXECUTE. The rewrites are only done once, but we need select_lex->sj_subselects list to be populated for every EXECUTE. */ if (optimizer_flag(thd, OPTIMIZER_SWITCH_MATERIALIZATION) && // 0 !child_select->is_part_of_union() && // 1 parent_unit->first_select()->leaf_tables.elements && // 2 thd->lex->sql_command == SQLCOM_SELECT && // * child_select->outer_select()->leaf_tables.elements && // 2A subquery_types_allow_materialization(in_subs) && (in_subs->is_top_level_item() || //3 optimizer_flag(thd, OPTIMIZER_SWITCH_PARTIAL_MATCH_ROWID_MERGE) || //3 optimizer_flag(thd, OPTIMIZER_SWITCH_PARTIAL_MATCH_TABLE_SCAN)) && //3 !in_subs->is_correlated) //4 { return TRUE; } return FALSE; } /* Check if we need JOIN::prepare()-phase subquery rewrites and if yes, do them SYNOPSIS check_and_do_in_subquery_rewrites() join Subquery's join DESCRIPTION Check if we need to do - subquery -> mergeable semi-join rewrite - if the subquery can be handled with materialization - 'substitution' rewrite for table-less subqueries like "(select 1)" - IN->EXISTS rewrite and, depending on the rewrite, either do it, or record it to be done at a later phase. RETURN 0 - OK Other - Some sort of query error */ int check_and_do_in_subquery_rewrites(JOIN *join) { THD *thd=join->thd; st_select_lex *select_lex= join->select_lex; st_select_lex_unit* parent_unit= select_lex->master_unit(); DBUG_ENTER("check_and_do_in_subquery_rewrites"); /* If 1) this join is inside a subquery (of any type except FROM-clause subquery) and 2) we aren't just normalizing a VIEW Then perform early unconditional subquery transformations: - Convert subquery predicate into semi-join, or - Mark the subquery for execution using materialization, or - Perform IN->EXISTS transformation, or - Perform more/less ALL/ANY -> MIN/MAX rewrite - Substitute trivial scalar-context subquery with its value TODO: for PS, make the whole block execute only on the first execution */ Item_subselect *subselect; if (!(thd->lex->context_analysis_only & CONTEXT_ANALYSIS_ONLY_VIEW) && // (1) (subselect= parent_unit->item)) // (2) { Item_in_subselect *in_subs= NULL; Item_allany_subselect *allany_subs= NULL; switch (subselect->substype()) { case Item_subselect::IN_SUBS: in_subs= (Item_in_subselect *)subselect; break; case Item_subselect::ALL_SUBS: case Item_subselect::ANY_SUBS: allany_subs= (Item_allany_subselect *)subselect; break; default: break; } /* Resolve expressions and perform semantic analysis for IN query */ if (in_subs != NULL) /* TODO: Add the condition below to this if statement when we have proper support for is_correlated handling for materialized semijoins. If we were to add this condition now, the fix_fields() call in convert_subq_to_sj() would force the flag is_correlated to be set erroneously for prepared queries. thd->stmt_arena->state != Query_arena::PREPARED) */ { /* Check if the left and right expressions have the same # of columns, i.e. we don't have a case like (oe1, oe2) IN (SELECT ie1, ie2, ie3 ...) TODO why do we have this duplicated in IN->EXISTS transformers? psergey-todo: fix these: grep for duplicated_subselect_card_check */ if (select_lex->item_list.elements != in_subs->left_expr->cols()) { my_error(ER_OPERAND_COLUMNS, MYF(0), in_subs->left_expr->cols()); DBUG_RETURN(-1); } SELECT_LEX *current= thd->lex->current_select; thd->lex->current_select= current->return_after_parsing(); char const *save_where= thd->where; thd->where= "IN/ALL/ANY subquery"; bool failure= !in_subs->left_expr->fixed && in_subs->left_expr->fix_fields(thd, &in_subs->left_expr); thd->lex->current_select= current; thd->where= save_where; if (failure) DBUG_RETURN(-1); /* purecov: deadcode */ } if (select_lex == parent_unit->fake_select_lex) { /* The join and its select_lex object represent the 'fake' select used to compute the result of a UNION. */ DBUG_RETURN(0); } DBUG_PRINT("info", ("Checking if subq can be converted to semi-join")); /* Check if we're in subquery that is a candidate for flattening into a semi-join (which is done in flatten_subqueries()). The requirements are: 1. Subquery predicate is an IN/=ANY subq predicate 2. Subquery is a single SELECT (not a UNION) 3. Subquery does not have GROUP BY or ORDER BY 4. Subquery does not use aggregate functions or HAVING 5. Subquery predicate is at the AND-top-level of ON/WHERE clause 6. We are not in a subquery of a single table UPDATE/DELETE that doesn't have a JOIN (TODO: We should handle this at some point by switching to multi-table UPDATE/DELETE) 7. We're not in a table-less subquery like "SELECT 1" 8. No execution method was already chosen (by a prepared statement) 9. Parent select is not a table-less select 10. Neither parent nor child select have STRAIGHT_JOIN option. */ if (optimizer_flag(thd, OPTIMIZER_SWITCH_SEMIJOIN) && in_subs && // 1 !select_lex->is_part_of_union() && // 2 !select_lex->group_list.elements && !join->order && // 3 !join->having && !select_lex->with_sum_func && // 4 in_subs->emb_on_expr_nest && // 5 select_lex->outer_select()->join && // 6 parent_unit->first_select()->leaf_tables.elements && // 7 !in_subs->has_strategy() && // 8 select_lex->outer_select()->leaf_tables.elements && // 9 !((join->select_options | // 10 select_lex->outer_select()->join->select_options) // 10 & SELECT_STRAIGHT_JOIN)) // 10 { DBUG_PRINT("info", ("Subquery is semi-join conversion candidate")); (void)subquery_types_allow_materialization(in_subs); in_subs->is_flattenable_semijoin= TRUE; /* Register the subquery for further processing in flatten_subqueries() */ if (!in_subs->is_registered_semijoin) { Query_arena *arena, backup; arena= thd->activate_stmt_arena_if_needed(&backup); select_lex->outer_select()->sj_subselects.push_back(in_subs); if (arena) thd->restore_active_arena(arena, &backup); in_subs->is_registered_semijoin= TRUE; } } else { DBUG_PRINT("info", ("Subquery can't be converted to merged semi-join")); /* Test if the user has set a legal combination of optimizer switches. */ if (!optimizer_flag(thd, OPTIMIZER_SWITCH_IN_TO_EXISTS) && !optimizer_flag(thd, OPTIMIZER_SWITCH_MATERIALIZATION)) my_error(ER_ILLEGAL_SUBQUERY_OPTIMIZER_SWITCHES, MYF(0)); /* If the subquery predicate is IN/=ANY, analyse and set all possible subquery execution strategies based on optimizer switches and syntactic properties. */ if (in_subs && !in_subs->has_strategy()) { if (is_materialization_applicable(thd, in_subs, select_lex)) { in_subs->add_strategy(SUBS_MATERIALIZATION); /* If the subquery is an AND-part of WHERE register for being processed with jtbm strategy */ if (in_subs->emb_on_expr_nest == NO_JOIN_NEST && optimizer_flag(thd, OPTIMIZER_SWITCH_SEMIJOIN)) { in_subs->is_flattenable_semijoin= FALSE; if (!in_subs->is_registered_semijoin) { Query_arena *arena, backup; arena= thd->activate_stmt_arena_if_needed(&backup); select_lex->outer_select()->sj_subselects.push_back(in_subs); if (arena) thd->restore_active_arena(arena, &backup); in_subs->is_registered_semijoin= TRUE; } } } /* IN-TO-EXISTS is the only universal strategy. Choose it if the user allowed it via an optimizer switch, or if materialization is not possible. */ if (optimizer_flag(thd, OPTIMIZER_SWITCH_IN_TO_EXISTS) || !in_subs->has_strategy()) in_subs->add_strategy(SUBS_IN_TO_EXISTS); } /* Check if max/min optimization applicable */ if (allany_subs && !allany_subs->is_set_strategy()) { uchar strategy= (allany_subs->is_maxmin_applicable(join) ? (SUBS_MAXMIN_INJECTED | SUBS_MAXMIN_ENGINE) : SUBS_IN_TO_EXISTS); allany_subs->add_strategy(strategy); } /* Transform each subquery predicate according to its overloaded transformer. */ if (subselect->select_transformer(join)) DBUG_RETURN(-1); } } DBUG_RETURN(0); } /** @brief Check if subquery's compared types allow materialization. @param in_subs Subquery predicate, updated as follows: types_allow_materialization TRUE if subquery materialization is allowed. sjm_scan_allowed If types_allow_materialization is TRUE, indicates whether it is possible to use subquery materialization and scan the materialized table. @retval TRUE If subquery types allow materialization. @retval FALSE Otherwise. @details This is a temporary fix for BUG#36752. There are two subquery materialization strategies: 1. Materialize and do index lookups in the materialized table. See BUG#36752 for description of restrictions we need to put on the compared expressions. 2. Materialize and then do a full scan of the materialized table. At the moment, this strategy's applicability criteria are even stricter than in #1. This is so because of the following: consider an uncorrelated subquery ...WHERE (ot1.col1, ot2.col2 ...) IN (SELECT ie1,ie2,... FROM it1 ...) and a join order that could be used to do sjm-materialization: SJM-Scan(it1, it1), ot1, ot2 IN-equalities will be parts of conditions attached to the outer tables: ot1: ot1.col1 = ie1 AND ... (C1) ot2: ot1.col2 = ie2 AND ... (C2) besides those there may be additional references to ie1 and ie2 generated by equality propagation. The problem with evaluating C1 and C2 is that ie{1,2} refer to subquery tables' columns, while we only have current value of materialization temptable. Our solution is to * require that all ie{N} are table column references. This allows to copy the values of materialization temptable columns to the original table's columns (see setup_sj_materialization for more details) * require that compared columns have exactly the same type. This is a temporary measure to avoid BUG#36752-type problems. */ static bool subquery_types_allow_materialization(Item_in_subselect *in_subs) { DBUG_ENTER("subquery_types_allow_materialization"); DBUG_ASSERT(in_subs->left_expr->fixed); List_iterator it(in_subs->unit->first_select()->item_list); uint elements= in_subs->unit->first_select()->item_list.elements; in_subs->types_allow_materialization= FALSE; // Assign default values in_subs->sjm_scan_allowed= FALSE; bool all_are_fields= TRUE; for (uint i= 0; i < elements; i++) { Item *outer= in_subs->left_expr->element_index(i); Item *inner= it++; all_are_fields &= (outer->real_item()->type() == Item::FIELD_ITEM && inner->real_item()->type() == Item::FIELD_ITEM); if (outer->cmp_type() != inner->cmp_type()) DBUG_RETURN(FALSE); switch (outer->cmp_type()) { case STRING_RESULT: if (!(outer->collation.collation == inner->collation.collation)) DBUG_RETURN(FALSE); // Materialization does not work with BLOB columns if (inner->field_type() == MYSQL_TYPE_BLOB || inner->field_type() == MYSQL_TYPE_GEOMETRY) DBUG_RETURN(FALSE); /* Materialization also is unable to work when create_tmp_table() will create a blob column because item->max_length is too big. The following check is copied from Item::make_string_field(): */ if (inner->max_length / inner->collation.collation->mbmaxlen > CONVERT_IF_BIGGER_TO_BLOB) { DBUG_RETURN(FALSE); } break; case TIME_RESULT: if (mysql_type_to_time_type(outer->field_type()) != mysql_type_to_time_type(outer->field_type())) DBUG_RETURN(FALSE); default: /* suitable for materialization */ break; } } in_subs->types_allow_materialization= TRUE; in_subs->sjm_scan_allowed= all_are_fields; DBUG_PRINT("info",("subquery_types_allow_materialization: ok, allowed")); DBUG_RETURN(TRUE); } /** Apply max min optimization of all/any subselect */ bool JOIN::transform_max_min_subquery() { DBUG_ENTER("JOIN::transform_max_min_subquery"); Item_subselect *subselect= unit->item; if (!subselect || (subselect->substype() != Item_subselect::ALL_SUBS && subselect->substype() != Item_subselect::ANY_SUBS)) DBUG_RETURN(0); DBUG_RETURN(((Item_allany_subselect *) subselect)-> transform_into_max_min(this)); } /* Finalize IN->EXISTS conversion in case we couldn't use materialization. DESCRIPTION Invoke the IN->EXISTS converter Replace the Item_in_subselect with its wrapper Item_in_optimizer in WHERE. RETURN FALSE - Ok TRUE - Fatal error */ bool make_in_exists_conversion(THD *thd, JOIN *join, Item_in_subselect *item) { DBUG_ENTER("make_in_exists_conversion"); JOIN *child_join= item->unit->first_select()->join; bool res; /* We're going to finalize IN->EXISTS conversion. Normally, IN->EXISTS conversion takes place inside the Item_subselect::fix_fields() call, where item_subselect->fixed==FALSE (as fix_fields() haven't finished yet) and item_subselect->changed==FALSE (as the conversion haven't been finalized) At the end of Item_subselect::fix_fields() we had to set fixed=TRUE, changed=TRUE (the only other option would have been to return error). So, now we have to set these back for the duration of select_transformer() call. */ item->changed= 0; item->fixed= 0; SELECT_LEX *save_select_lex= thd->lex->current_select; thd->lex->current_select= item->unit->first_select(); res= item->select_transformer(child_join); thd->lex->current_select= save_select_lex; if (res) DBUG_RETURN(TRUE); item->changed= 1; item->fixed= 1; Item *substitute= item->substitution; bool do_fix_fields= !item->substitution->fixed; /* The Item_subselect has already been wrapped with Item_in_optimizer, so we should search for item->optimizer, not 'item'. */ Item *replace_me= item->optimizer; DBUG_ASSERT(replace_me==substitute); Item **tree= (item->emb_on_expr_nest == NO_JOIN_NEST)? &join->conds : &(item->emb_on_expr_nest->on_expr); if (replace_where_subcondition(join, tree, replace_me, substitute, do_fix_fields)) DBUG_RETURN(TRUE); item->substitution= NULL; /* If this is a prepared statement, repeat the above operation for prep_where (or prep_on_expr). */ if (!thd->stmt_arena->is_conventional()) { tree= (item->emb_on_expr_nest == (TABLE_LIST*)NO_JOIN_NEST)? &join->select_lex->prep_where : &(item->emb_on_expr_nest->prep_on_expr); if (replace_where_subcondition(join, tree, replace_me, substitute, FALSE)) DBUG_RETURN(TRUE); } DBUG_RETURN(FALSE); } bool check_for_outer_joins(List *join_list) { TABLE_LIST *table; NESTED_JOIN *nested_join; List_iterator li(*join_list); while ((table= li++)) { if ((nested_join= table->nested_join)) { if (check_for_outer_joins(&nested_join->join_list)) return TRUE; } if (table->outer_join) return TRUE; } return FALSE; } /* Convert semi-join subquery predicates into semi-join join nests SYNOPSIS convert_join_subqueries_to_semijoins() DESCRIPTION Convert candidate subquery predicates into semi-join join nests. This transformation is performed once in query lifetime and is irreversible. Conversion of one subquery predicate ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ We start with a join that has a semi-join subquery: SELECT ... FROM ot, ... WHERE oe IN (SELECT ie FROM it1 ... itN WHERE subq_where) AND outer_where and convert it into a semi-join nest: SELECT ... FROM ot SEMI JOIN (it1 ... itN), ... WHERE outer_where AND subq_where AND oe=ie that is, in order to do the conversion, we need to * Create the "SEMI JOIN (it1 .. itN)" part and add it into the parent query's FROM structure. * Add "AND subq_where AND oe=ie" into parent query's WHERE (or ON if the subquery predicate was in an ON expression) * Remove the subquery predicate from the parent query's WHERE Considerations when converting many predicates ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ A join may have at most MAX_TABLES tables. This may prevent us from flattening all subqueries when the total number of tables in parent and child selects exceeds MAX_TABLES. We deal with this problem by flattening children's subqueries first and then using a heuristic rule to determine each subquery predicate's "priority". RETURN FALSE OK TRUE Error */ bool convert_join_subqueries_to_semijoins(JOIN *join) { Query_arena *arena, backup; Item_in_subselect *in_subq; THD *thd= join->thd; List_iterator ti(join->select_lex->leaf_tables); DBUG_ENTER("convert_join_subqueries_to_semijoins"); if (join->select_lex->sj_subselects.is_empty()) DBUG_RETURN(FALSE); List_iterator_fast li(join->select_lex->sj_subselects); while ((in_subq= li++)) { SELECT_LEX *subq_sel= in_subq->get_select_lex(); if (subq_sel->handle_derived(thd->lex, DT_OPTIMIZE)) DBUG_RETURN(1); if (subq_sel->handle_derived(thd->lex, DT_MERGE)) DBUG_RETURN(TRUE); subq_sel->update_used_tables(); } li.rewind(); /* First, convert child join's subqueries. We proceed bottom-up here */ while ((in_subq= li++)) { st_select_lex *child_select= in_subq->get_select_lex(); JOIN *child_join= child_select->join; child_join->outer_tables = child_join->table_count; /* child_select->where contains only the WHERE predicate of the subquery itself here. We may be selecting from a VIEW, which has its own predicate. The combined predicates are available in child_join->conds, which was built by setup_conds() doing prepare_where() for all views. */ child_select->where= child_join->conds; if (convert_join_subqueries_to_semijoins(child_join)) DBUG_RETURN(TRUE); in_subq->sj_convert_priority= test(in_subq->emb_on_expr_nest != NO_JOIN_NEST) * MAX_TABLES * 2 + in_subq->is_correlated * MAX_TABLES + child_join->outer_tables; } // Temporary measure: disable semi-joins when they are together with outer // joins. #if 0 if (check_for_outer_joins(join->join_list)) { in_subq= join->select_lex->sj_subselects.head(); arena= thd->activate_stmt_arena_if_needed(&backup); goto skip_conversion; } #endif //dump_TABLE_LIST_struct(select_lex, select_lex->leaf_tables); /* 2. Pick which subqueries to convert: sort the subquery array - prefer correlated subqueries over uncorrelated; - prefer subqueries that have greater number of outer tables; */ bubble_sort(&join->select_lex->sj_subselects, subq_sj_candidate_cmp, NULL); // #tables-in-parent-query + #tables-in-subquery < MAX_TABLES /* Replace all subqueries to be flattened with Item_int(1) */ arena= thd->activate_stmt_arena_if_needed(&backup); li.rewind(); while ((in_subq= li++)) { bool remove_item= TRUE; /* Stop processing if we've reached a subquery that's attached to the ON clause */ if (in_subq->emb_on_expr_nest != NO_JOIN_NEST) break; if (in_subq->is_flattenable_semijoin) { if (join->table_count + in_subq->unit->first_select()->join->table_count >= MAX_TABLES) break; if (convert_subq_to_sj(join, in_subq)) goto restore_arena_and_fail; } else { if (join->table_count + 1 >= MAX_TABLES) break; if (convert_subq_to_jtbm(join, in_subq, &remove_item)) goto restore_arena_and_fail; } if (remove_item) { Item **tree= (in_subq->emb_on_expr_nest == NO_JOIN_NEST)? &join->conds : &(in_subq->emb_on_expr_nest->on_expr); Item *replace_me= in_subq->original_item(); if (replace_where_subcondition(join, tree, replace_me, new Item_int(1), FALSE)) goto restore_arena_and_fail; } } //skip_conversion: /* 3. Finalize (perform IN->EXISTS rewrite) the subqueries that we didn't convert: */ while (in_subq) { JOIN *child_join= in_subq->unit->first_select()->join; in_subq->changed= 0; in_subq->fixed= 0; SELECT_LEX *save_select_lex= thd->lex->current_select; thd->lex->current_select= in_subq->unit->first_select(); bool res= in_subq->select_transformer(child_join); thd->lex->current_select= save_select_lex; if (res) DBUG_RETURN(TRUE); in_subq->changed= 1; in_subq->fixed= 1; Item *substitute= in_subq->substitution; bool do_fix_fields= !in_subq->substitution->fixed; Item **tree= (in_subq->emb_on_expr_nest == NO_JOIN_NEST)? &join->conds : &(in_subq->emb_on_expr_nest->on_expr); Item *replace_me= in_subq->original_item(); if (replace_where_subcondition(join, tree, replace_me, substitute, do_fix_fields)) DBUG_RETURN(TRUE); in_subq->substitution= NULL; /* If this is a prepared statement, repeat the above operation for prep_where (or prep_on_expr). Subquery-to-semijoin conversion is done once for prepared statement. */ if (!thd->stmt_arena->is_conventional()) { tree= (in_subq->emb_on_expr_nest == NO_JOIN_NEST)? &join->select_lex->prep_where : &(in_subq->emb_on_expr_nest->prep_on_expr); /* prep_on_expr/ prep_where may be NULL in some cases. If that is the case, do nothing - simplify_joins() will copy ON/WHERE expression into prep_on_expr/prep_where. */ if (*tree && replace_where_subcondition(join, tree, replace_me, substitute, FALSE)) DBUG_RETURN(TRUE); } /* Revert to the IN->EXISTS strategy in the rare case when the subquery could not be flattened. */ in_subq->reset_strategy(SUBS_IN_TO_EXISTS); if (is_materialization_applicable(thd, in_subq, in_subq->unit->first_select())) { in_subq->add_strategy(SUBS_MATERIALIZATION); } in_subq= li++; } if (arena) thd->restore_active_arena(arena, &backup); join->select_lex->sj_subselects.empty(); DBUG_RETURN(FALSE); restore_arena_and_fail: if (arena) thd->restore_active_arena(arena, &backup); DBUG_RETURN(TRUE); } /* Get #output_rows and scan_time estimates for a "delayed" table. SYNOPSIS get_delayed_table_estimates() table IN Table to get estimates for out_rows OUT E(#rows in the table) scan_time OUT E(scan_time). startup_cost OUT cost to populate the table. DESCRIPTION Get #output_rows and scan_time estimates for a "delayed" table. By "delayed" here we mean that the table is filled at the start of query execution. This means that the optimizer can't use table statistics to get #rows estimate for it, it has to call this function instead. This function is expected to make different actions depending on the nature of the table. At the moment there is only one kind of delayed tables, non-flattenable semi-joins. */ void get_delayed_table_estimates(TABLE *table, ha_rows *out_rows, double *scan_time, double *startup_cost) { Item_in_subselect *item= table->pos_in_table_list->jtbm_subselect; DBUG_ASSERT(item->engine->engine_type() == subselect_engine::HASH_SJ_ENGINE); subselect_hash_sj_engine *hash_sj_engine= ((subselect_hash_sj_engine*)item->engine); *out_rows= (ha_rows)item->jtbm_record_count; *startup_cost= item->jtbm_read_time; /* Calculate cost of scanning the temptable */ double data_size= item->jtbm_record_count * hash_sj_engine->tmp_table->s->reclength; /* Do like in handler::read_time */ *scan_time= data_size/IO_SIZE + 2; } /** @brief Replaces an expression destructively inside the expression tree of the WHERE clase. @note Because of current requirements for semijoin flattening, we do not need to recurse here, hence this function will only examine the top-level AND conditions. (see JOIN::prepare, comment starting with "Check if the subquery predicate can be executed via materialization". @param join The top-level query. @param old_cond The expression to be replaced. @param new_cond The expression to be substituted. @param do_fix_fields If true, Item::fix_fields(THD*, Item**) is called for the new expression. @return true if there was an error, false if successful. */ static bool replace_where_subcondition(JOIN *join, Item **expr, Item *old_cond, Item *new_cond, bool do_fix_fields) { if (*expr == old_cond) { *expr= new_cond; if (do_fix_fields) new_cond->fix_fields(join->thd, expr); return FALSE; } if ((*expr)->type() == Item::COND_ITEM) { List_iterator li(*((Item_cond*)(*expr))->argument_list()); Item *item; while ((item= li++)) { if (item == old_cond) { li.replace(new_cond); if (do_fix_fields) new_cond->fix_fields(join->thd, li.ref()); return FALSE; } } } /* We can come to here when - we're doing replace operations on both on_expr and prep_on_expr - on_expr is the same as prep_on_expr, or they share a sub-tree (so, when we do replace in on_expr, we replace in prep_on_expr, too, and when we try doing a replace in prep_on_expr, the item we wanted to replace there has already been replaced) */ return FALSE; } static int subq_sj_candidate_cmp(Item_in_subselect* el1, Item_in_subselect* el2, void *arg) { return (el1->sj_convert_priority > el2->sj_convert_priority) ? 1 : ( (el1->sj_convert_priority == el2->sj_convert_priority)? 0 : -1); } /* Convert a subquery predicate into a TABLE_LIST semi-join nest SYNOPSIS convert_subq_to_sj() parent_join Parent join, the one that has subq_pred in its WHERE/ON clause subq_pred Subquery predicate to be converted DESCRIPTION Convert a subquery predicate into a TABLE_LIST semi-join nest. All the prerequisites are already checked, so the conversion is always successfull. Prepared Statements: the transformation is permanent: - Changes in TABLE_LIST structures are naturally permanent - Item tree changes are performed on statement MEM_ROOT: = we activate statement MEM_ROOT = this function is called before the first fix_prepare_information call. This is intended because the criteria for subquery-to-sj conversion remain constant for the lifetime of the Prepared Statement. RETURN FALSE OK TRUE Out of memory error */ static bool convert_subq_to_sj(JOIN *parent_join, Item_in_subselect *subq_pred) { SELECT_LEX *parent_lex= parent_join->select_lex; TABLE_LIST *emb_tbl_nest= NULL; List *emb_join_list= &parent_lex->top_join_list; THD *thd= parent_join->thd; DBUG_ENTER("convert_subq_to_sj"); /* 1. Find out where to put the predicate into. Note: for "t1 LEFT JOIN t2" this will be t2, a leaf. */ if ((void*)subq_pred->emb_on_expr_nest != (void*)NO_JOIN_NEST) { if (subq_pred->emb_on_expr_nest->nested_join) { /* We're dealing with ... [LEFT] JOIN ( ... ) ON (subquery AND whatever) ... The sj-nest will be inserted into the brackets nest. */ emb_tbl_nest= subq_pred->emb_on_expr_nest; emb_join_list= &emb_tbl_nest->nested_join->join_list; } else if (!subq_pred->emb_on_expr_nest->outer_join) { /* We're dealing with ... INNER JOIN tblX ON (subquery AND whatever) ... The sj-nest will be tblX's "sibling", i.e. another child of its parent. This is ok because tblX is joined as an inner join. */ emb_tbl_nest= subq_pred->emb_on_expr_nest->embedding; if (emb_tbl_nest) emb_join_list= &emb_tbl_nest->nested_join->join_list; } else if (!subq_pred->emb_on_expr_nest->nested_join) { TABLE_LIST *outer_tbl= subq_pred->emb_on_expr_nest; TABLE_LIST *wrap_nest; /* We're dealing with ... LEFT JOIN tbl ON (on_expr AND subq_pred) ... we'll need to convert it into: ... LEFT JOIN ( tbl SJ (subq_tables) ) ON (on_expr AND subq_pred) ... | | |<----- wrap_nest ---->| Q: other subqueries may be pointing to this element. What to do? A1: simple solution: copy *subq_pred->expr_join_nest= *parent_nest. But we'll need to fix other pointers. A2: Another way: have TABLE_LIST::next_ptr so the following subqueries know the table has been nested. A3: changes in the TABLE_LIST::outer_join will make everything work automatically. */ if (!(wrap_nest= alloc_join_nest(parent_join->thd))) { DBUG_RETURN(TRUE); } wrap_nest->embedding= outer_tbl->embedding; wrap_nest->join_list= outer_tbl->join_list; wrap_nest->alias= (char*) "(sj-wrap)"; wrap_nest->nested_join->join_list.empty(); wrap_nest->nested_join->join_list.push_back(outer_tbl); outer_tbl->embedding= wrap_nest; outer_tbl->join_list= &wrap_nest->nested_join->join_list; /* wrap_nest will take place of outer_tbl, so move the outer join flag and on_expr */ wrap_nest->outer_join= outer_tbl->outer_join; outer_tbl->outer_join= 0; wrap_nest->on_expr= outer_tbl->on_expr; outer_tbl->on_expr= NULL; List_iterator li(*wrap_nest->join_list); TABLE_LIST *tbl; while ((tbl= li++)) { if (tbl == outer_tbl) { li.replace(wrap_nest); break; } } /* Ok now wrap_nest 'contains' outer_tbl and we're ready to add the semi-join nest into it */ emb_join_list= &wrap_nest->nested_join->join_list; emb_tbl_nest= wrap_nest; } } TABLE_LIST *sj_nest; NESTED_JOIN *nested_join; if (!(sj_nest= alloc_join_nest(parent_join->thd))) { DBUG_RETURN(TRUE); } nested_join= sj_nest->nested_join; sj_nest->join_list= emb_join_list; sj_nest->embedding= emb_tbl_nest; sj_nest->alias= (char*) "(sj-nest)"; sj_nest->sj_subq_pred= subq_pred; /* Nests do not participate in those 'chains', so: */ /* sj_nest->next_leaf= sj_nest->next_local= sj_nest->next_global == NULL*/ emb_join_list->push_back(sj_nest); /* nested_join->used_tables and nested_join->not_null_tables are initialized in simplify_joins(). */ /* 2. Walk through subquery's top list and set 'embedding' to point to the sj-nest. */ st_select_lex *subq_lex= subq_pred->unit->first_select(); nested_join->join_list.empty(); List_iterator_fast li(subq_lex->top_join_list); TABLE_LIST *tl; while ((tl= li++)) { tl->embedding= sj_nest; tl->join_list= &nested_join->join_list; nested_join->join_list.push_back(tl); } /* Reconnect the next_leaf chain. TODO: Do we have to put subquery's tables at the end of the chain? Inserting them at the beginning would be a bit faster. NOTE: We actually insert them at the front! That's because the order is reversed in this list. */ parent_lex->leaf_tables.concat(&subq_lex->leaf_tables); /* Same as above for next_local chain (a theory: a next_local chain always starts with ::leaf_tables because view's tables are inserted after the view) */ for (tl= parent_lex->leaf_tables.head(); tl->next_local; tl= tl->next_local) ; tl->next_local= subq_lex->leaf_tables.head(); /* A theory: no need to re-connect the next_global chain */ /* 3. Remove the original subquery predicate from the WHERE/ON */ // The subqueries were replaced for Item_int(1) earlier subq_pred->reset_strategy(SUBS_SEMI_JOIN); // for subsequent executions /*TODO: also reset the 'with_subselect' there. */ /* n. Adjust the parent_join->table_count counter */ uint table_no= parent_join->table_count; /* n. Walk through child's tables and adjust table->map */ List_iterator_fast si(subq_lex->leaf_tables); while ((tl= si++)) { tl->table->tablenr= table_no; tl->table->map= ((table_map)1) << table_no; if (tl->is_jtbm()) tl->jtbm_table_no= tl->table->tablenr; SELECT_LEX *old_sl= tl->select_lex; tl->select_lex= parent_join->select_lex; for (TABLE_LIST *emb= tl->embedding; emb && emb->select_lex == old_sl; emb= emb->embedding) emb->select_lex= parent_join->select_lex; table_no++; } parent_join->table_count += subq_lex->join->table_count; //parent_join->table_count += subq_lex->leaf_tables.elements; /* Put the subquery's WHERE into semi-join's sj_on_expr Add the subquery-induced equalities too. */ SELECT_LEX *save_lex= thd->lex->current_select; thd->lex->current_select=subq_lex; if (!subq_pred->left_expr->fixed && subq_pred->left_expr->fix_fields(thd, &subq_pred->left_expr)) DBUG_RETURN(TRUE); thd->lex->current_select=save_lex; sj_nest->nested_join->sj_corr_tables= subq_pred->used_tables(); sj_nest->nested_join->sj_depends_on= subq_pred->used_tables() | subq_pred->left_expr->used_tables(); sj_nest->sj_on_expr= subq_lex->join->conds; /* Create the IN-equalities and inject them into semi-join's ON expression. Additionally, for LooseScan strategy - Record the number of IN-equalities. - Create list of pointers to (oe1, ..., ieN). We'll need the list to see which of the expressions are bound and which are not (for those we'll produce a distinct stream of (ie_i1,...ie_ik). (TODO: can we just create a list of pointers and hope the expressions will not substitute themselves on fix_fields()? or we need to wrap them into Item_direct_view_refs and store pointers to those. The pointers to Item_direct_view_refs are guaranteed to be stable as Item_direct_view_refs doesn't substitute itself with anything in Item_direct_view_ref::fix_fields. */ sj_nest->sj_in_exprs= subq_pred->left_expr->cols(); sj_nest->nested_join->sj_outer_expr_list.empty(); if (subq_pred->left_expr->cols() == 1) { nested_join->sj_outer_expr_list.push_back(subq_pred->left_expr); Item_func_eq *item_eq= new Item_func_eq(subq_pred->left_expr, subq_lex->ref_pointer_array[0]); item_eq->in_equality_no= 0; sj_nest->sj_on_expr= and_items(sj_nest->sj_on_expr, item_eq); } else { for (uint i= 0; i < subq_pred->left_expr->cols(); i++) { nested_join->sj_outer_expr_list.push_back(subq_pred->left_expr-> element_index(i)); Item_func_eq *item_eq= new Item_func_eq(subq_pred->left_expr->element_index(i), subq_lex->ref_pointer_array[i]); item_eq->in_equality_no= i; sj_nest->sj_on_expr= and_items(sj_nest->sj_on_expr, item_eq); } } /* Fix the created equality and AND */ if (!sj_nest->sj_on_expr->fixed) sj_nest->sj_on_expr->fix_fields(parent_join->thd, &sj_nest->sj_on_expr); /* Walk through sj nest's WHERE and ON expressions and call item->fix_table_changes() for all items. */ sj_nest->sj_on_expr->fix_after_pullout(parent_lex, &sj_nest->sj_on_expr); fix_list_after_tbl_changes(parent_lex, &sj_nest->nested_join->join_list); /* Unlink the child select_lex so it doesn't show up in EXPLAIN: */ subq_lex->master_unit()->exclude_level(); DBUG_EXECUTE("where", print_where(sj_nest->sj_on_expr,"SJ-EXPR", QT_ORDINARY);); /* Inject sj_on_expr into the parent's WHERE or ON */ if (emb_tbl_nest) { emb_tbl_nest->on_expr= and_items(emb_tbl_nest->on_expr, sj_nest->sj_on_expr); emb_tbl_nest->on_expr->top_level_item(); if (!emb_tbl_nest->on_expr->fixed) emb_tbl_nest->on_expr->fix_fields(parent_join->thd, &emb_tbl_nest->on_expr); } else { /* Inject into the WHERE */ parent_join->conds= and_items(parent_join->conds, sj_nest->sj_on_expr); parent_join->conds->top_level_item(); /* fix_fields must update the properties (e.g. st_select_lex::cond_count of the correct select_lex. */ save_lex= thd->lex->current_select; thd->lex->current_select=parent_join->select_lex; if (!parent_join->conds->fixed) parent_join->conds->fix_fields(parent_join->thd, &parent_join->conds); thd->lex->current_select=save_lex; parent_join->select_lex->where= parent_join->conds; } if (subq_lex->ftfunc_list->elements) { Item_func_match *ifm; List_iterator_fast li(*(subq_lex->ftfunc_list)); while ((ifm= li++)) parent_lex->ftfunc_list->push_front(ifm); } DBUG_RETURN(FALSE); } const int SUBQERY_TEMPTABLE_NAME_MAX_LEN= 20; static void create_subquery_temptable_name(char *to, uint number) { DBUG_ASSERT(number < 10000); to= strmov(to, "select_lex; List *emb_join_list= &parent_lex->top_join_list; TABLE_LIST *emb_tbl_nest= NULL; // will change when we learn to handle outer joins TABLE_LIST *tl; double rows; double read_time; DBUG_ENTER("convert_subq_to_jtbm"); subq_pred->set_strategy(SUBS_MATERIALIZATION); if (subq_pred->optimize(&rows, &read_time)) DBUG_RETURN(TRUE); subq_pred->jtbm_read_time= read_time; subq_pred->jtbm_record_count=rows; subq_pred->is_jtbm_merged= TRUE; if (subq_pred->engine->engine_type() != subselect_engine::HASH_SJ_ENGINE) { *remove_item= FALSE; DBUG_RETURN(FALSE); } *remove_item= TRUE; TABLE_LIST *jtbm; char *tbl_alias; if (!(tbl_alias= (char*)parent_join->thd->calloc(SUBQERY_TEMPTABLE_NAME_MAX_LEN)) || !(jtbm= alloc_join_nest(parent_join->thd))) //todo: this is not a join nest! { DBUG_RETURN(TRUE); } jtbm->join_list= emb_join_list; jtbm->embedding= emb_tbl_nest; jtbm->jtbm_subselect= subq_pred; jtbm->nested_join= NULL; /* Nests do not participate in those 'chains', so: */ /* jtbm->next_leaf= jtbm->next_local= jtbm->next_global == NULL*/ emb_join_list->push_back(jtbm); /* Inject the jtbm table into TABLE_LIST::next_leaf list, so that make_join_statistics() and co. can find it. */ parent_lex->leaf_tables.push_back(jtbm); /* Same as above for TABLE_LIST::next_local chain (a theory: a next_local chain always starts with ::leaf_tables because view's tables are inserted after the view) */ for (tl= parent_lex->leaf_tables.head(); tl->next_local; tl= tl->next_local) {} tl->next_local= jtbm; /* A theory: no need to re-connect the next_global chain */ subselect_hash_sj_engine *hash_sj_engine= ((subselect_hash_sj_engine*)subq_pred->engine); jtbm->table= hash_sj_engine->tmp_table; jtbm->table->tablenr= parent_join->table_count; jtbm->table->map= table_map(1) << (parent_join->table_count); jtbm->jtbm_table_no= jtbm->table->tablenr; parent_join->table_count++; DBUG_ASSERT(parent_join->table_count < MAX_TABLES); Item *conds= hash_sj_engine->semi_join_conds; conds->fix_after_pullout(parent_lex, &conds); DBUG_EXECUTE("where", print_where(conds,"SJ-EXPR", QT_ORDINARY);); create_subquery_temptable_name(tbl_alias, hash_sj_engine->materialize_join-> select_lex->select_number); jtbm->alias= tbl_alias; #if 0 /* Inject sj_on_expr into the parent's WHERE or ON */ if (emb_tbl_nest) { DBUG_ASSERT(0); /*emb_tbl_nest->on_expr= and_items(emb_tbl_nest->on_expr, sj_nest->sj_on_expr); emb_tbl_nest->on_expr->fix_fields(parent_join->thd, &emb_tbl_nest->on_expr); */ } else { /* Inject into the WHERE */ parent_join->conds= and_items(parent_join->conds, conds); parent_join->conds->fix_fields(parent_join->thd, &parent_join->conds); parent_join->select_lex->where= parent_join->conds; } #endif /* Don't unlink the child subselect, as the subquery will be used. */ DBUG_RETURN(FALSE); } static TABLE_LIST *alloc_join_nest(THD *thd) { TABLE_LIST *tbl; if (!(tbl= (TABLE_LIST*) thd->calloc(ALIGN_SIZE(sizeof(TABLE_LIST))+ sizeof(NESTED_JOIN)))) return NULL; tbl->nested_join= (NESTED_JOIN*) ((uchar*)tbl + ALIGN_SIZE(sizeof(TABLE_LIST))); return tbl; } void fix_list_after_tbl_changes(SELECT_LEX *new_parent, List *tlist) { List_iterator it(*tlist); TABLE_LIST *table; while ((table= it++)) { if (table->on_expr) table->on_expr->fix_after_pullout(new_parent, &table->on_expr); if (table->nested_join) fix_list_after_tbl_changes(new_parent, &table->nested_join->join_list); } } static void set_emb_join_nest(List *tables, TABLE_LIST *emb_sj_nest) { List_iterator it(*tables); TABLE_LIST *tbl; while ((tbl= it++)) { /* Note: check for nested_join first. derived-merged tables have tbl->table!=NULL && tbl->table->reginfo==NULL. */ if (tbl->nested_join) set_emb_join_nest(&tbl->nested_join->join_list, emb_sj_nest); else if (tbl->table) tbl->table->reginfo.join_tab->emb_sj_nest= emb_sj_nest; } } /* Pull tables out of semi-join nests, if possible SYNOPSIS pull_out_semijoin_tables() join The join where to do the semi-join flattening DESCRIPTION Try to pull tables out of semi-join nests. PRECONDITIONS When this function is called, the join may have several semi-join nests but it is guaranteed that one semi-join nest does not contain another. ACTION A table can be pulled out of the semi-join nest if - It is a constant table, or - It is accessed via eq_ref(outer_tables) POSTCONDITIONS * Tables that were pulled out have JOIN_TAB::emb_sj_nest == NULL * Tables that were not pulled out have JOIN_TAB::emb_sj_nest pointing to semi-join nest they are in. * Semi-join nests' TABLE_LIST::sj_inner_tables is updated accordingly This operation is (and should be) performed at each PS execution since tables may become/cease to be constant across PS reexecutions. NOTE Table pullout may make uncorrelated subquery correlated. Consider this example: ... WHERE oe IN (SELECT it1.primary_key WHERE p(it1, it2) ... ) here table it1 can be pulled out (we have it1.primary_key=oe which gives us functional dependency). Once it1 is pulled out, all references to it1 from p(it1, it2) become references to outside of the subquery and thus make the subquery (i.e. its semi-join nest) correlated. Making the subquery (i.e. its semi-join nest) correlated prevents us from using Materialization or LooseScan to execute it. RETURN 0 - OK 1 - Out of memory error */ int pull_out_semijoin_tables(JOIN *join) { TABLE_LIST *sj_nest; DBUG_ENTER("pull_out_semijoin_tables"); List_iterator sj_list_it(join->select_lex->sj_nests); /* Try pulling out of the each of the semi-joins */ while ((sj_nest= sj_list_it++)) { List_iterator child_li(sj_nest->nested_join->join_list); TABLE_LIST *tbl; /* Don't do table pull-out for nested joins (if we get nested joins here, it means these are outer joins. It is theoretically possible to do pull-out for some of the outer tables but we dont support this currently. */ bool have_join_nest_children= FALSE; set_emb_join_nest(&sj_nest->nested_join->join_list, sj_nest); while ((tbl= child_li++)) { if (tbl->nested_join) { have_join_nest_children= TRUE; break; } } table_map pulled_tables= 0; if (have_join_nest_children) goto skip; /* Action #1: Mark the constant tables to be pulled out */ child_li.rewind(); while ((tbl= child_li++)) { if (tbl->table) { tbl->table->reginfo.join_tab->emb_sj_nest= sj_nest; #if 0 /* Do not pull out tables because they are constant. This operation has a problem: - Some constant tables may become/cease to be constant across PS re-executions - Contrary to our initial assumption, it turned out that table pullout operation is not easily undoable. The solution is to leave constant tables where they are. This will affect only constant tables that are 1-row or empty, tables that are constant because they are accessed via eq_ref(const) access will still be pulled out as functionally-dependent. This will cause us to miss the chance to flatten some of the subqueries, but since const tables do not generate many duplicates, it really doesn't matter that much whether they were pulled out or not. All of this was done as fix for BUG#43768. */ if (tbl->table->map & join->const_table_map) { pulled_tables |= tbl->table->map; DBUG_PRINT("info", ("Table %s pulled out (reason: constant)", tbl->table->alias)); } #endif } } /* Action #2: Find which tables we can pull out based on update_ref_and_keys() data. Note that pulling one table out can allow us to pull out some other tables too. */ bool pulled_a_table; do { pulled_a_table= FALSE; child_li.rewind(); while ((tbl= child_li++)) { if (tbl->table && !(pulled_tables & tbl->table->map)) { if (find_eq_ref_candidate(tbl->table, sj_nest->nested_join->used_tables & ~pulled_tables)) { pulled_a_table= TRUE; pulled_tables |= tbl->table->map; DBUG_PRINT("info", ("Table %s pulled out (reason: func dep)", tbl->table->alias.c_ptr())); /* Pulling a table out of uncorrelated subquery in general makes makes it correlated. See the NOTE to this funtion. */ sj_nest->sj_subq_pred->is_correlated= TRUE; sj_nest->nested_join->sj_corr_tables|= tbl->table->map; sj_nest->nested_join->sj_depends_on|= tbl->table->map; } } } } while (pulled_a_table); child_li.rewind(); skip: /* Action #3: Move the pulled out TABLE_LIST elements to the parents. */ table_map inner_tables= sj_nest->nested_join->used_tables & ~pulled_tables; /* Record the bitmap of inner tables */ sj_nest->sj_inner_tables= inner_tables; if (pulled_tables) { List *upper_join_list= (sj_nest->embedding != NULL)? (&sj_nest->embedding->nested_join->join_list): (&join->select_lex->top_join_list); Query_arena *arena, backup; arena= join->thd->activate_stmt_arena_if_needed(&backup); while ((tbl= child_li++)) { if (tbl->table) { if (inner_tables & tbl->table->map) { /* This table is not pulled out */ tbl->table->reginfo.join_tab->emb_sj_nest= sj_nest; } else { /* This table has been pulled out of the semi-join nest */ tbl->table->reginfo.join_tab->emb_sj_nest= NULL; /* Pull the table up in the same way as simplify_joins() does: update join_list and embedding pointers but keep next[_local] pointers. */ child_li.remove(); sj_nest->nested_join->used_tables &= ~tbl->table->map; upper_join_list->push_back(tbl); tbl->join_list= upper_join_list; tbl->embedding= sj_nest->embedding; } } } /* Remove the sj-nest itself if we've removed everything from it */ if (!inner_tables) { List_iterator li(*upper_join_list); /* Find the sj_nest in the list. */ while (sj_nest != li++) ; li.remove(); /* Also remove it from the list of SJ-nests: */ sj_list_it.remove(); } if (arena) join->thd->restore_active_arena(arena, &backup); } } DBUG_RETURN(0); } /* Optimize semi-join nests that could be run with sj-materialization SYNOPSIS optimize_semijoin_nests() join The join to optimize semi-join nests for all_table_map Bitmap of all tables in the join DESCRIPTION Optimize each of the semi-join nests that can be run with materialization. For each of the nests, we - Generate the best join order for this "sub-join" and remember it; - Remember the sub-join execution cost (it's part of materialization cost); - Calculate other costs that will be incurred if we decide to use materialization strategy for this semi-join nest. All obtained information is saved and will be used by the main join optimization pass. NOTES Because of Join::reoptimize(), this function may be called multiple times. RETURN FALSE Ok TRUE Out of memory error */ bool optimize_semijoin_nests(JOIN *join, table_map all_table_map) { DBUG_ENTER("optimize_semijoin_nests"); List_iterator sj_list_it(join->select_lex->sj_nests); TABLE_LIST *sj_nest; while ((sj_nest= sj_list_it++)) { /* semi-join nests with only constant tables are not valid */ /// DBUG_ASSERT(sj_nest->sj_inner_tables & ~join->const_table_map); sj_nest->sj_mat_info= NULL; /* The statement may have been executed with 'semijoin=on' earlier. We need to verify that 'semijoin=on' still holds. */ if (optimizer_flag(join->thd, OPTIMIZER_SWITCH_SEMIJOIN) && optimizer_flag(join->thd, OPTIMIZER_SWITCH_MATERIALIZATION)) { if ((sj_nest->sj_inner_tables & ~join->const_table_map) && /* not everything was pulled out */ !sj_nest->sj_subq_pred->is_correlated && sj_nest->sj_subq_pred->types_allow_materialization) { join->emb_sjm_nest= sj_nest; if (choose_plan(join, all_table_map &~join->const_table_map)) DBUG_RETURN(TRUE); /* purecov: inspected */ /* The best plan to run the subquery is now in join->best_positions, save it. */ uint n_tables= my_count_bits(sj_nest->sj_inner_tables & ~join->const_table_map); SJ_MATERIALIZATION_INFO* sjm; if (!(sjm= new SJ_MATERIALIZATION_INFO) || !(sjm->positions= (POSITION*)join->thd->alloc(sizeof(POSITION)* n_tables))) DBUG_RETURN(TRUE); /* purecov: inspected */ sjm->tables= n_tables; sjm->is_used= FALSE; double subjoin_out_rows, subjoin_read_time; /* join->get_partial_cost_and_fanout(n_tables + join->const_tables, table_map(-1), &subjoin_read_time, &subjoin_out_rows); */ join->get_prefix_cost_and_fanout(n_tables, &subjoin_read_time, &subjoin_out_rows); sjm->materialization_cost.convert_from_cost(subjoin_read_time); sjm->rows= subjoin_out_rows; // Don't use the following list because it has "stale" items. use // ref_pointer_array instead: // //List &right_expr_list= // sj_nest->sj_subq_pred->unit->first_select()->item_list; /* Adjust output cardinality estimates. If the subquery has form ... oe IN (SELECT t1.colX, t2.colY, func(X,Y,Z) ) then the number of distinct output record combinations has an upper bound of product of number of records matching the tables that are used by the SELECT clause. TODO: We can get a more precise estimate if we - use rec_per_key cardinality estimates. For simple cases like "oe IN (SELECT t.key ...)" it is trivial. - Functional dependencies between the tables in the semi-join nest (the payoff is probably less here?) See also get_post_group_estimate(). */ SELECT_LEX *subq_select= sj_nest->sj_subq_pred->unit->first_select(); { for (uint i=0 ; i < join->const_tables + sjm->tables ; i++) { JOIN_TAB *tab= join->best_positions[i].table; join->map2table[tab->table->tablenr]= tab; } //List_iterator it(right_expr_list); Item **ref_array= subq_select->ref_pointer_array; Item **ref_array_end= ref_array + subq_select->item_list.elements; table_map map= 0; //while ((item= it++)) for (;ref_array < ref_array_end; ref_array++) map |= (*ref_array)->used_tables(); map= map & ~PSEUDO_TABLE_BITS; Table_map_iterator tm_it(map); int tableno; double rows= 1.0; while ((tableno = tm_it.next_bit()) != Table_map_iterator::BITMAP_END) rows *= join->map2table[tableno]->table->quick_condition_rows; sjm->rows= min(sjm->rows, rows); } memcpy(sjm->positions, join->best_positions + join->const_tables, sizeof(POSITION) * n_tables); /* Calculate temporary table parameters and usage costs */ uint rowlen= get_tmp_table_rec_length(subq_select->ref_pointer_array, subq_select->item_list.elements); double lookup_cost= get_tmp_table_lookup_cost(join->thd, subjoin_out_rows, rowlen); double write_cost= get_tmp_table_write_cost(join->thd, subjoin_out_rows, rowlen); /* Let materialization cost include the cost to write the data into the temporary table: */ sjm->materialization_cost.add_io(subjoin_out_rows, write_cost); /* Set the cost to do a full scan of the temptable (will need this to consider doing sjm-scan): */ sjm->scan_cost.zero(); sjm->scan_cost.add_io(sjm->rows, lookup_cost); sjm->lookup_cost.convert_from_cost(lookup_cost); sj_nest->sj_mat_info= sjm; DBUG_EXECUTE("opt", print_sjm(sjm);); } } } join->emb_sjm_nest= NULL; DBUG_RETURN(FALSE); } /* Get estimated record length for semi-join materialization temptable SYNOPSIS get_tmp_table_rec_length() items IN subquery's select list. DESCRIPTION Calculate estimated record length for semi-join materialization temptable. It's an estimate because we don't follow every bit of create_tmp_table()'s logic. This isn't necessary as the return value of this function is used only for cost calculations. RETURN Length of the temptable record, in bytes */ static uint get_tmp_table_rec_length(Item **p_items, uint elements) { uint len= 0; Item *item; //List_iterator it(items); Item **p_item; for (p_item= p_items; p_item < p_items + elements ; p_item++) { item = *p_item; switch (item->result_type()) { case REAL_RESULT: len += sizeof(double); break; case INT_RESULT: if (item->max_length >= (MY_INT32_NUM_DECIMAL_DIGITS - 1)) len += 8; else len += 4; break; case STRING_RESULT: enum enum_field_types type; /* DATE/TIME and GEOMETRY fields have STRING_RESULT result type. */ if ((type= item->field_type()) == MYSQL_TYPE_DATETIME || type == MYSQL_TYPE_TIME || type == MYSQL_TYPE_DATE || type == MYSQL_TYPE_TIMESTAMP || type == MYSQL_TYPE_GEOMETRY) len += 8; else len += item->max_length; break; case DECIMAL_RESULT: len += 10; break; case ROW_RESULT: default: DBUG_ASSERT(0); /* purecov: deadcode */ break; } } return len; } /** The cost of a lookup into a unique hash/btree index on a temporary table with 'row_count' rows each of size 'row_size'. @param thd current query context @param row_count number of rows in the temp table @param row_size average size in bytes of the rows @return the cost of one lookup */ static double get_tmp_table_lookup_cost(THD *thd, double row_count, uint row_size) { if (row_count * row_size > thd->variables.max_heap_table_size) return (double) DISK_TEMPTABLE_LOOKUP_COST; else return (double) HEAP_TEMPTABLE_LOOKUP_COST; } /** The cost of writing a row into a temporary table with 'row_count' unique rows each of size 'row_size'. @param thd current query context @param row_count number of rows in the temp table @param row_size average size in bytes of the rows @return the cost of writing one row */ static double get_tmp_table_write_cost(THD *thd, double row_count, uint row_size) { double lookup_cost= get_tmp_table_lookup_cost(thd, row_count, row_size); /* TODO: This is an optimistic estimate. Add additional costs resulting from actually writing the row to memory/disk and possible index reorganization. */ return lookup_cost; } /* Check if table's KEYUSE elements have an eq_ref(outer_tables) candidate SYNOPSIS find_eq_ref_candidate() table Table to be checked sj_inner_tables Bitmap of inner tables. eq_ref(inner_table) doesn't count. DESCRIPTION Check if table's KEYUSE elements have an eq_ref(outer_tables) candidate TODO Check again if it is feasible to factor common parts with constant table search Also check if it's feasible to factor common parts with table elimination RETURN TRUE - There exists an eq_ref(outer-tables) candidate FALSE - Otherwise */ bool find_eq_ref_candidate(TABLE *table, table_map sj_inner_tables) { KEYUSE *keyuse= table->reginfo.join_tab->keyuse; if (keyuse) { do { uint key= keyuse->key; KEY *keyinfo; key_part_map bound_parts= 0; bool is_excluded_key= keyuse->is_for_hash_join(); if (!is_excluded_key) { keyinfo= table->key_info + key; is_excluded_key= !test(keyinfo->flags & HA_NOSAME); } if (!is_excluded_key) { do /* For all equalities on all key parts */ { /* Check if this is "t.keypart = expr(outer_tables) */ if (!(keyuse->used_tables & sj_inner_tables) && !(keyuse->optimize & KEY_OPTIMIZE_REF_OR_NULL)) { bound_parts |= 1 << keyuse->keypart; } keyuse++; } while (keyuse->key == key && keyuse->table == table); if (bound_parts == PREV_BITS(uint, keyinfo->key_parts)) return TRUE; } else { do { keyuse++; } while (keyuse->key == key && keyuse->table == table); } } while (keyuse->table == table); } return FALSE; } /* Do semi-join optimization step after we've added a new tab to join prefix SYNOPSIS advance_sj_state() join The join we're optimizing remaining_tables Tables not in the join prefix new_join_tab Join tab we've just added to the join prefix idx Index of this join tab (i.e. number of tables in the prefix minus one) current_record_count INOUT Estimate of #records in join prefix's output current_read_time INOUT Cost to execute the join prefix loose_scan_pos IN A POSITION with LooseScan plan to access table new_join_tab (produced by the last best_access_path call) DESCRIPTION Update semi-join optimization state after we've added another tab (table and access method) to the join prefix. The state is maintained in join->positions[#prefix_size]. Each of the available strategies has its own state variables. for each semi-join strategy { update strategy's state variables; if (join prefix has all the tables that are needed to consider using this strategy for the semi-join(s)) { calculate cost of using the strategy if ((this is the first strategy to handle the semi-join nest(s) || the cost is less than other strategies)) { // Pick this strategy pos->sj_strategy= .. .. } } Most of the new state is saved join->positions[idx] (and hence no undo is necessary). Several members of class JOIN are updated also, these changes can be rolled back with restore_prev_sj_state(). See setup_semijoin_dups_elimination() for a description of what kinds of join prefixes each strategy can handle. */ void advance_sj_state(JOIN *join, table_map remaining_tables, const JOIN_TAB *new_join_tab, uint idx, double *current_record_count, double *current_read_time, POSITION *loose_scan_pos) { TABLE_LIST *emb_sj_nest; POSITION *pos= join->positions + idx; remaining_tables &= ~new_join_tab->table->map; bool disable_jbuf= join->thd->variables.join_cache_level == 0; pos->prefix_cost.convert_from_cost(*current_read_time); pos->prefix_record_count= *current_record_count; pos->sj_strategy= SJ_OPT_NONE; pos->prefix_dups_producing_tables= join->cur_dups_producing_tables; /* We're performing optimization inside SJ-Materialization nest */ if (join->emb_sjm_nest) { pos->invalidate_firstmatch_prefix(); pos->first_loosescan_table= MAX_TABLES; pos->dupsweedout_tables= 0; pos->sjm_scan_need_tables= 0; return; } /* Initialize the state or copy it from prev. tables */ if (idx == join->const_tables) { pos->invalidate_firstmatch_prefix(); pos->first_loosescan_table= MAX_TABLES; pos->dupsweedout_tables= 0; pos->sjm_scan_need_tables= 0; LINT_INIT(pos->sjm_scan_last_inner); } else { // FirstMatch pos->first_firstmatch_table= (pos[-1].sj_strategy == SJ_OPT_FIRST_MATCH) ? MAX_TABLES : pos[-1].first_firstmatch_table; pos->first_firstmatch_rtbl= pos[-1].first_firstmatch_rtbl; pos->firstmatch_need_tables= pos[-1].firstmatch_need_tables; // LooseScan pos->first_loosescan_table= (pos[-1].sj_strategy == SJ_OPT_LOOSE_SCAN) ? MAX_TABLES : pos[-1].first_loosescan_table; pos->loosescan_need_tables= pos[-1].loosescan_need_tables; // SJ-Materialization Scan pos->sjm_scan_need_tables= (pos[-1].sj_strategy == SJ_OPT_MATERIALIZE_SCAN) ? 0 : pos[-1].sjm_scan_need_tables; pos->sjm_scan_last_inner= pos[-1].sjm_scan_last_inner; // Duplicate Weedout pos->dupsweedout_tables= pos[-1].dupsweedout_tables; pos->first_dupsweedout_table= pos[-1].first_dupsweedout_table; } table_map handled_by_fm_or_ls= 0; /* FirstMatch Strategy */ if (new_join_tab->emb_sj_nest && optimizer_flag(join->thd, OPTIMIZER_SWITCH_FIRSTMATCH) && !join->outer_join) { const table_map outer_corr_tables= new_join_tab->emb_sj_nest->nested_join->sj_corr_tables | new_join_tab->emb_sj_nest->nested_join->sj_depends_on; const table_map sj_inner_tables= new_join_tab->emb_sj_nest->sj_inner_tables & ~join->const_table_map; /* Enter condition: 1. The next join tab belongs to semi-join nest (verified for the encompassing code block above). 2. We're not in a duplicate producer range yet 3. All outer tables that - the subquery is correlated with, or - referred to from the outer_expr are in the join prefix 4. All inner tables are still part of remaining_tables. */ if (!join->cur_sj_inner_tables && // (2) !(remaining_tables & outer_corr_tables) && // (3) (sj_inner_tables == // (4) ((remaining_tables | new_join_tab->table->map) & sj_inner_tables))) { /* Start tracking potential FirstMatch range */ pos->first_firstmatch_table= idx; pos->firstmatch_need_tables= sj_inner_tables; pos->first_firstmatch_rtbl= remaining_tables; } if (pos->in_firstmatch_prefix()) { if (outer_corr_tables & pos->first_firstmatch_rtbl) { /* Trying to add an sj-inner table whose sj-nest has an outer correlated table that was not in the prefix. This means FirstMatch can't be used. */ pos->invalidate_firstmatch_prefix(); } else { /* Record that we need all of this semi-join's inner tables, too */ pos->firstmatch_need_tables|= sj_inner_tables; } if (pos->in_firstmatch_prefix() && !(pos->firstmatch_need_tables & remaining_tables)) { /* Got a complete FirstMatch range. Calculate correct costs and fanout */ optimize_wo_join_buffering(join, pos->first_firstmatch_table, idx, remaining_tables, FALSE, idx, current_record_count, current_read_time); /* We don't yet know what are the other strategies, so pick the FirstMatch. We ought to save the alternate POSITIONs produced by optimize_wo_join_buffering but the problem is that providing save space uses too much space. Instead, we will re-calculate the alternate POSITIONs after we've picked the best QEP. */ pos->sj_strategy= SJ_OPT_FIRST_MATCH; handled_by_fm_or_ls= pos->firstmatch_need_tables; } } } /* LooseScan Strategy */ { POSITION *first=join->positions+pos->first_loosescan_table; /* LooseScan strategy can't handle interleaving between tables from the semi-join that LooseScan is handling and any other tables. If we were considering LooseScan for the join prefix (1) and the table we're adding creates an interleaving (2) then stop considering loose scan */ if ((pos->first_loosescan_table != MAX_TABLES) && // (1) (first->table->emb_sj_nest->sj_inner_tables & remaining_tables) && //(2) new_join_tab->emb_sj_nest != first->table->emb_sj_nest) //(2) { pos->first_loosescan_table= MAX_TABLES; } /* If we got an option to use LooseScan for the current table, start considering using LooseScan strategy */ if (loose_scan_pos->read_time != DBL_MAX && !join->outer_join) { pos->first_loosescan_table= idx; pos->loosescan_need_tables= new_join_tab->emb_sj_nest->sj_inner_tables | new_join_tab->emb_sj_nest->nested_join->sj_depends_on | new_join_tab->emb_sj_nest->nested_join->sj_corr_tables; } if ((pos->first_loosescan_table != MAX_TABLES) && !(remaining_tables & pos->loosescan_need_tables)) { /* Ok we have LooseScan plan and also have all LooseScan sj-nest's inner tables and outer correlated tables into the prefix. */ first=join->positions + pos->first_loosescan_table; uint n_tables= my_count_bits(first->table->emb_sj_nest->sj_inner_tables); /* Got a complete LooseScan range. Calculate its cost */ /* The same problem as with FirstMatch - we need to save POSITIONs somewhere but reserving space for all cases would require too much space. We will re-calculate POSITION structures later on. */ optimize_wo_join_buffering(join, pos->first_loosescan_table, idx, remaining_tables, TRUE, //first_alt disable_jbuf ? join->table_count : pos->first_loosescan_table + n_tables, current_record_count, current_read_time); /* We don't yet have any other strategies that could handle this semi-join nest (the other options are Duplicate Elimination or Materialization, which need at least the same set of tables in the join prefix to be considered) so unconditionally pick the LooseScan. */ pos->sj_strategy= SJ_OPT_LOOSE_SCAN; handled_by_fm_or_ls= first->table->emb_sj_nest->sj_inner_tables; } } /* Update join->cur_sj_inner_tables (Used by FirstMatch in this function and LooseScan detector in best_access_path) */ if ((emb_sj_nest= new_join_tab->emb_sj_nest)) { join->cur_sj_inner_tables |= emb_sj_nest->sj_inner_tables; join->cur_dups_producing_tables |= emb_sj_nest->sj_inner_tables; /* Remove the sj_nest if all of its SJ-inner tables are in cur_table_map */ if (!(remaining_tables & emb_sj_nest->sj_inner_tables & ~new_join_tab->table->map)) join->cur_sj_inner_tables &= ~emb_sj_nest->sj_inner_tables; } join->cur_dups_producing_tables &= ~handled_by_fm_or_ls; /* 4. SJ-Materialization and SJ-Materialization-scan strategy handler */ bool sjm_scan; SJ_MATERIALIZATION_INFO *mat_info; if ((mat_info= at_sjmat_pos(join, remaining_tables, new_join_tab, idx, &sjm_scan))) { if (sjm_scan) { /* We can't yet evaluate this option yet. This is because we can't accout for fanout of sj-inner tables yet: ntX SJM-SCAN(it1 ... itN) | ot1 ... otN | ^(1) ^(2) we're now at position (1). SJM temptable in general has multiple records, so at point (1) we'll get the fanout from sj-inner tables (ie there will be multiple record combinations). The final join result will not contain any semi-join produced fanout, i.e. tables within SJM-SCAN(...) will not contribute to the cardinality of the join output. Extra fanout produced by SJM-SCAN(...) will be 'absorbed' into fanout produced by ot1 ... otN. The simple way to model this is to remove SJM-SCAN(...) fanout once we reach the point #2. */ pos->sjm_scan_need_tables= new_join_tab->emb_sj_nest->sj_inner_tables | new_join_tab->emb_sj_nest->nested_join->sj_depends_on | new_join_tab->emb_sj_nest->nested_join->sj_corr_tables; pos->sjm_scan_last_inner= idx; } else { /* This is SJ-Materialization with lookups */ COST_VECT prefix_cost; signed int first_tab= (int)idx - mat_info->tables; double prefix_rec_count; if (first_tab < (int)join->const_tables) { prefix_cost.zero(); prefix_rec_count= 1.0; } else { prefix_cost= join->positions[first_tab].prefix_cost; prefix_rec_count= join->positions[first_tab].prefix_record_count; } double mat_read_time= prefix_cost.total_cost(); mat_read_time += mat_info->materialization_cost.total_cost() + prefix_rec_count * mat_info->lookup_cost.total_cost(); if (mat_read_time < *current_read_time || join->cur_dups_producing_tables) { /* NOTE: When we pick to use SJM[-Scan] we don't memcpy its POSITION elements to join->positions as that makes it hard to return things back when making one step back in join optimization. That's done after the QEP has been chosen. */ pos->sj_strategy= SJ_OPT_MATERIALIZE; *current_read_time= mat_read_time; *current_record_count= prefix_rec_count; join->cur_dups_producing_tables&= ~new_join_tab->emb_sj_nest->sj_inner_tables; } } } /* 4.A SJM-Scan second phase check */ if (pos->sjm_scan_need_tables && /* Have SJM-Scan prefix */ !(pos->sjm_scan_need_tables & remaining_tables)) { TABLE_LIST *mat_nest= join->positions[pos->sjm_scan_last_inner].table->emb_sj_nest; SJ_MATERIALIZATION_INFO *mat_info= mat_nest->sj_mat_info; double prefix_cost; double prefix_rec_count; int first_tab= pos->sjm_scan_last_inner + 1 - mat_info->tables; /* Get the prefix cost */ if (first_tab == (int)join->const_tables) { prefix_rec_count= 1.0; prefix_cost= 0.0; } else { prefix_cost= join->positions[first_tab - 1].prefix_cost.total_cost(); prefix_rec_count= join->positions[first_tab - 1].prefix_record_count; } /* Add materialization cost */ prefix_cost += mat_info->materialization_cost.total_cost() + prefix_rec_count * mat_info->scan_cost.total_cost(); prefix_rec_count *= mat_info->rows; uint i; table_map rem_tables= remaining_tables; for (i= idx; i != (first_tab + mat_info->tables - 1); i--) rem_tables |= join->positions[i].table->table->map; POSITION curpos, dummy; /* Need to re-run best-access-path as we prefix_rec_count has changed */ for (i= first_tab + mat_info->tables; i <= idx; i++) { best_access_path(join, join->positions[i].table, rem_tables, i, disable_jbuf, prefix_rec_count, &curpos, &dummy); prefix_rec_count *= curpos.records_read; prefix_cost += curpos.read_time; } /* Use the strategy if * it is cheaper then what we've had, or * we haven't picked any other semi-join strategy yet In the second case, we pick this strategy unconditionally because comparing cost without semi-join duplicate removal with cost with duplicate removal is not an apples-to-apples comparison. */ if (prefix_cost < *current_read_time || join->cur_dups_producing_tables) { pos->sj_strategy= SJ_OPT_MATERIALIZE_SCAN; *current_read_time= prefix_cost; *current_record_count= prefix_rec_count; join->cur_dups_producing_tables&= ~mat_nest->sj_inner_tables; } } /* 5. Duplicate Weedout strategy handler */ { /* Duplicate weedout can be applied after all ON-correlated and correlated */ TABLE_LIST *nest; if ((nest= new_join_tab->emb_sj_nest)) { if (!pos->dupsweedout_tables) pos->first_dupsweedout_table= idx; pos->dupsweedout_tables |= nest->sj_inner_tables | nest->nested_join->sj_depends_on | nest->nested_join->sj_corr_tables; } if (pos->dupsweedout_tables) { /* we're in the process of constructing a DuplicateWeedout range */ TABLE_LIST *emb= new_join_tab->table->pos_in_table_list->embedding; /* and we've entered an inner side of an outer join*/ if (emb && emb->on_expr) pos->dupsweedout_tables |= emb->nested_join->used_tables; } if (pos->dupsweedout_tables && !(remaining_tables & ~new_join_tab->table->map & pos->dupsweedout_tables)) { /* Ok, reached a state where we could put a dups weedout point. Walk back and calculate - the join cost (this is needed as the accumulated cost may assume some other duplicate elimination method) - extra fanout that will be removed by duplicate elimination - duplicate elimination cost There are two cases: 1. We have other strategy/ies to remove all of the duplicates. 2. We don't. We need to calculate the cost in case #2 also because we need to make choice between this join order and others. */ uint first_tab= pos->first_dupsweedout_table; double dups_cost; double prefix_rec_count; double sj_inner_fanout= 1.0; double sj_outer_fanout= 1.0; uint temptable_rec_size; if (first_tab == join->const_tables) { prefix_rec_count= 1.0; temptable_rec_size= 0; dups_cost= 0.0; } else { dups_cost= join->positions[first_tab - 1].prefix_cost.total_cost(); prefix_rec_count= join->positions[first_tab - 1].prefix_record_count; temptable_rec_size= 8; /* This is not true but we'll make it so */ } table_map dups_removed_fanout= 0; for (uint j= pos->first_dupsweedout_table; j <= idx; j++) { POSITION *p= join->positions + j; dups_cost += p->read_time; if (p->table->emb_sj_nest) { sj_inner_fanout *= p->records_read; dups_removed_fanout |= p->table->table->map; } else { sj_outer_fanout *= p->records_read; temptable_rec_size += p->table->table->file->ref_length; } } /* Add the cost of temptable use. The table will have sj_outer_fanout records, and we will make - sj_outer_fanout table writes - sj_inner_fanout*sj_outer_fanout lookups. */ double one_lookup_cost= get_tmp_table_lookup_cost(join->thd, sj_outer_fanout, temptable_rec_size); double one_write_cost= get_tmp_table_write_cost(join->thd, sj_outer_fanout, temptable_rec_size); double write_cost= join->positions[first_tab].prefix_record_count* sj_outer_fanout * one_write_cost; double full_lookup_cost= join->positions[first_tab].prefix_record_count* sj_outer_fanout* sj_inner_fanout * one_lookup_cost; dups_cost += write_cost + full_lookup_cost; /* Use the strategy if * it is cheaper then what we've had, or * we haven't picked any other semi-join strategy yet The second part is necessary because this strategy is the last one to consider (it needs "the most" tables in the prefix) and we can't leave duplicate-producing tables not handled by any strategy. */ if (dups_cost < *current_read_time || join->cur_dups_producing_tables) { pos->sj_strategy= SJ_OPT_DUPS_WEEDOUT; *current_read_time= dups_cost; *current_record_count= prefix_rec_count * sj_outer_fanout; join->cur_dups_producing_tables &= ~dups_removed_fanout; } } } } /* Remove the last join tab from from join->cur_sj_inner_tables bitmap we assume remaining_tables doesnt contain @tab. */ void restore_prev_sj_state(const table_map remaining_tables, const JOIN_TAB *tab, uint idx) { TABLE_LIST *emb_sj_nest; if ((emb_sj_nest= tab->emb_sj_nest)) { /* If we're removing the last SJ-inner table, remove the sj-nest */ if ((remaining_tables & emb_sj_nest->sj_inner_tables) == (emb_sj_nest->sj_inner_tables & ~tab->table->map)) { tab->join->cur_sj_inner_tables &= ~emb_sj_nest->sj_inner_tables; } } POSITION *pos= tab->join->positions + idx; tab->join->cur_dups_producing_tables= pos->prefix_dups_producing_tables; } /* Given a semi-join nest, find out which of the IN-equalities are bound SYNOPSIS get_bound_sj_equalities() sj_nest Semi-join nest remaining_tables Tables that are not yet bound DESCRIPTION Given a semi-join nest, find out which of the IN-equalities have their left part expression bound (i.e. the said expression doesn't refer to any of remaining_tables and can be evaluated). RETURN Bitmap of bound IN-equalities. */ ulonglong get_bound_sj_equalities(TABLE_LIST *sj_nest, table_map remaining_tables) { List_iterator li(sj_nest->nested_join->sj_outer_expr_list); Item *item; uint i= 0; ulonglong res= 0; while ((item= li++)) { /* Q: should this take into account equality propagation and how? A: If e->outer_side is an Item_field, walk over the equality class and see if there is an element that is bound? (this is an optional feature) */ if (!(item->used_tables() & remaining_tables)) { res |= 1ULL << i; } i++; } return res; } /* Check if the last tables of the partial join order allow to use sj-materialization strategy for them SYNOPSIS at_sjmat_pos() join remaining_tables tab the last table's join tab idx last table's index loose_scan OUT TRUE <=> use LooseScan RETURN TRUE Yes, can apply sj-materialization FALSE No, some of the requirements are not met */ static SJ_MATERIALIZATION_INFO * at_sjmat_pos(const JOIN *join, table_map remaining_tables, const JOIN_TAB *tab, uint idx, bool *loose_scan) { /* Check if 1. We're in a semi-join nest that can be run with SJ-materialization 2. All the tables correlated through the IN subquery are in the prefix */ TABLE_LIST *emb_sj_nest= tab->emb_sj_nest; table_map suffix= remaining_tables & ~tab->table->map; if (emb_sj_nest && emb_sj_nest->sj_mat_info && !(suffix & emb_sj_nest->sj_inner_tables)) { /* Walk back and check if all immediately preceding tables are from this semi-join. */ uint n_tables= my_count_bits(tab->emb_sj_nest->sj_inner_tables); for (uint i= 1; i < n_tables ; i++) { if (join->positions[idx - i].table->emb_sj_nest != tab->emb_sj_nest) return NULL; } *loose_scan= test(remaining_tables & ~tab->table->map & (emb_sj_nest->sj_inner_tables | emb_sj_nest->nested_join->sj_depends_on)); if (*loose_scan && !emb_sj_nest->sj_subq_pred->sjm_scan_allowed) return NULL; else return emb_sj_nest->sj_mat_info; } return NULL; } /* Fix semi-join strategies for the picked join order SYNOPSIS fix_semijoin_strategies_for_picked_join_order() join The join with the picked join order DESCRIPTION Fix semi-join strategies for the picked join order. This is a step that needs to be done right after we have fixed the join order. What we do here is switch join's semi-join strategy description from backward-based to forwards based. When join optimization is in progress, we re-consider semi-join strategies after we've added another table. Here's an illustration. Suppose the join optimization is underway: 1) ot1 it1 it2 sjX -- looking at (ot1, it1, it2) join prefix, we decide to use semi-join strategy sjX. 2) ot1 it1 it2 ot2 sjX sjY -- Having added table ot2, we now may consider another semi-join strategy and decide to use a different strategy sjY. Note that the record of sjX has remained under it2. That is necessary because we need to be able to get back to (ot1, it1, it2) join prefix. what makes things even worse is that there are cases where the choice of sjY changes the way we should access it2. 3) [ot1 it1 it2 ot2 ot3] sjX sjY -- This means that after join optimization is finished, semi-join info should be read right-to-left (while nearly all plan refinement functions, EXPLAIN, etc proceed from left to right) This function does the needed reversal, making it possible to read the join and semi-join order from left to right. */ void fix_semijoin_strategies_for_picked_join_order(JOIN *join) { uint table_count=join->table_count; uint tablenr; table_map remaining_tables= 0; table_map handled_tabs= 0; for (tablenr= table_count - 1 ; tablenr != join->const_tables - 1; tablenr--) { POSITION *pos= join->best_positions + tablenr; JOIN_TAB *s= pos->table; uint first; LINT_INIT(first); // Set by every branch except SJ_OPT_NONE which doesn't use it if ((handled_tabs & s->table->map) || pos->sj_strategy == SJ_OPT_NONE) { remaining_tables |= s->table->map; continue; } if (pos->sj_strategy == SJ_OPT_MATERIALIZE) { SJ_MATERIALIZATION_INFO *sjm= s->emb_sj_nest->sj_mat_info; sjm->is_used= TRUE; sjm->is_sj_scan= FALSE; memcpy(pos - sjm->tables + 1, sjm->positions, sizeof(POSITION) * sjm->tables); first= tablenr - sjm->tables + 1; join->best_positions[first].n_sj_tables= sjm->tables; join->best_positions[first].sj_strategy= SJ_OPT_MATERIALIZE; } else if (pos->sj_strategy == SJ_OPT_MATERIALIZE_SCAN) { POSITION *first_inner= join->best_positions + pos->sjm_scan_last_inner; SJ_MATERIALIZATION_INFO *sjm= first_inner->table->emb_sj_nest->sj_mat_info; sjm->is_used= TRUE; sjm->is_sj_scan= TRUE; first= pos->sjm_scan_last_inner - sjm->tables + 1; memcpy(join->best_positions + first, sjm->positions, sizeof(POSITION) * sjm->tables); join->best_positions[first].sj_strategy= SJ_OPT_MATERIALIZE_SCAN; join->best_positions[first].n_sj_tables= sjm->tables; /* Do what advance_sj_state did: re-run best_access_path for every table in the [last_inner_table + 1; pos..) range */ double prefix_rec_count; /* Get the prefix record count */ if (first == join->const_tables) prefix_rec_count= 1.0; else prefix_rec_count= join->best_positions[first-1].prefix_record_count; /* Add materialization record count*/ prefix_rec_count *= sjm->rows; uint i; table_map rem_tables= remaining_tables; for (i= tablenr; i != (first + sjm->tables - 1); i--) rem_tables |= join->best_positions[i].table->table->map; POSITION dummy; join->cur_sj_inner_tables= 0; for (i= first + sjm->tables; i <= tablenr; i++) { best_access_path(join, join->best_positions[i].table, rem_tables, i, FALSE, prefix_rec_count, join->best_positions + i, &dummy); prefix_rec_count *= join->best_positions[i].records_read; rem_tables &= ~join->best_positions[i].table->table->map; } } if (pos->sj_strategy == SJ_OPT_FIRST_MATCH) { first= pos->first_firstmatch_table; join->best_positions[first].sj_strategy= SJ_OPT_FIRST_MATCH; join->best_positions[first].n_sj_tables= tablenr - first + 1; POSITION dummy; // For loose scan paths double record_count= (first== join->const_tables)? 1.0: join->best_positions[tablenr - 1].prefix_record_count; table_map rem_tables= remaining_tables; uint idx; for (idx= first; idx <= tablenr; idx++) { rem_tables |= join->best_positions[idx].table->table->map; } /* Re-run best_access_path to produce best access methods that do not use join buffering */ join->cur_sj_inner_tables= 0; for (idx= first; idx <= tablenr; idx++) { if (join->best_positions[idx].use_join_buffer) { best_access_path(join, join->best_positions[idx].table, rem_tables, idx, TRUE /* no jbuf */, record_count, join->best_positions + idx, &dummy); } record_count *= join->best_positions[idx].records_read; rem_tables &= ~join->best_positions[idx].table->table->map; } } if (pos->sj_strategy == SJ_OPT_LOOSE_SCAN) { first= pos->first_loosescan_table; POSITION *first_pos= join->best_positions + first; POSITION loose_scan_pos; // For loose scan paths double record_count= (first== join->const_tables)? 1.0: join->best_positions[tablenr - 1].prefix_record_count; table_map rem_tables= remaining_tables; uint idx; for (idx= first; idx <= tablenr; idx++) rem_tables |= join->best_positions[idx].table->table->map; /* Re-run best_access_path to produce best access methods that do not use join buffering */ join->cur_sj_inner_tables= 0; for (idx= first; idx <= tablenr; idx++) { if (join->best_positions[idx].use_join_buffer || (idx == first)) { best_access_path(join, join->best_positions[idx].table, rem_tables, idx, TRUE /* no jbuf */, record_count, join->best_positions + idx, &loose_scan_pos); if (idx==first) join->best_positions[idx]= loose_scan_pos; } rem_tables &= ~join->best_positions[idx].table->table->map; record_count *= join->best_positions[idx].records_read; } first_pos->sj_strategy= SJ_OPT_LOOSE_SCAN; first_pos->n_sj_tables= my_count_bits(first_pos->table->emb_sj_nest->sj_inner_tables); } if (pos->sj_strategy == SJ_OPT_DUPS_WEEDOUT) { /* Duplicate Weedout starting at pos->first_dupsweedout_table, ending at this table. */ first= pos->first_dupsweedout_table; join->best_positions[first].sj_strategy= SJ_OPT_DUPS_WEEDOUT; join->best_positions[first].n_sj_tables= tablenr - first + 1; } uint i_end= first + join->best_positions[first].n_sj_tables; for (uint i= first; i < i_end; i++) { if (i != first) join->best_positions[i].sj_strategy= SJ_OPT_NONE; handled_tabs |= join->best_positions[i].table->table->map; } if (tablenr != first) pos->sj_strategy= SJ_OPT_NONE; remaining_tables |= s->table->map; //s->sj_strategy= pos->sj_strategy; join->join_tab[first].sj_strategy= join->best_positions[first].sj_strategy; join->join_tab[first].n_sj_tables= join->best_positions[first].n_sj_tables; } } /* Setup semi-join materialization strategy for one semi-join nest SYNOPSIS setup_sj_materialization() tab The first tab in the semi-join DESCRIPTION Setup execution structures for one semi-join materialization nest: - Create the materialization temporary table - If we're going to do index lookups create TABLE_REF structure to make the lookus - else (if we're going to do a full scan of the temptable) create Copy_field structures to do copying. RETURN FALSE Ok TRUE Error */ bool setup_sj_materialization_part1(JOIN_TAB *sjm_tab) { DBUG_ENTER("setup_sj_materialization"); JOIN_TAB *tab= sjm_tab->bush_children->start; TABLE_LIST *emb_sj_nest= tab->table->pos_in_table_list->embedding; /* Walk out of outer join nests until we reach the semi-join nest we're in */ while (!emb_sj_nest->sj_mat_info) emb_sj_nest= emb_sj_nest->embedding; SJ_MATERIALIZATION_INFO *sjm= emb_sj_nest->sj_mat_info; THD *thd= tab->join->thd; /* First the calls come to the materialization function */ //List &item_list= emb_sj_nest->sj_subq_pred->unit->first_select()->item_list; DBUG_ASSERT(sjm->is_used); /* Set up the table to write to, do as select_union::create_result_table does */ sjm->sjm_table_param.init(); sjm->sjm_table_param.bit_fields_as_long= TRUE; //List_iterator it(item_list); SELECT_LEX *subq_select= emb_sj_nest->sj_subq_pred->unit->first_select(); Item **p_item= subq_select->ref_pointer_array; Item **p_end= p_item + subq_select->item_list.elements; //while((right_expr= it++)) for(;p_item != p_end; p_item++) sjm->sjm_table_cols.push_back(*p_item); sjm->sjm_table_param.field_count= subq_select->item_list.elements; if (!(sjm->table= create_tmp_table(thd, &sjm->sjm_table_param, sjm->sjm_table_cols, (ORDER*) 0, TRUE /* distinct */, 1, /*save_sum_fields*/ thd->variables.option_bits | TMP_TABLE_ALL_COLUMNS, HA_POS_ERROR /*rows_limit */, (char*)"sj-materialize"))) DBUG_RETURN(TRUE); /* purecov: inspected */ sjm->table->file->extra(HA_EXTRA_WRITE_CACHE); sjm->table->file->extra(HA_EXTRA_IGNORE_DUP_KEY); tab->join->sj_tmp_tables.push_back(sjm->table); tab->join->sjm_info_list.push_back(sjm); sjm->materialized= FALSE; sjm_tab->table= sjm->table; sjm->table->pos_in_table_list= emb_sj_nest; DBUG_RETURN(FALSE); } bool setup_sj_materialization_part2(JOIN_TAB *sjm_tab) { DBUG_ENTER("setup_sj_materialization_part2"); JOIN_TAB *tab= sjm_tab->bush_children->start; TABLE_LIST *emb_sj_nest= tab->table->pos_in_table_list->embedding; /* Walk out of outer join nests until we reach the semi-join nest we're in */ while (!emb_sj_nest->sj_mat_info) emb_sj_nest= emb_sj_nest->embedding; SJ_MATERIALIZATION_INFO *sjm= emb_sj_nest->sj_mat_info; THD *thd= tab->join->thd; uint i; //List &item_list= emb_sj_nest->sj_subq_pred->unit->first_select()->item_list; //List_iterator it(item_list); if (!sjm->is_sj_scan) { KEY *tmp_key; /* The only index on the temporary table. */ uint tmp_key_parts; /* Number of keyparts in tmp_key. */ tmp_key= sjm->table->key_info; tmp_key_parts= tmp_key->key_parts; /* Create/initialize everything we will need to index lookups into the temptable. */ TABLE_REF *tab_ref; tab_ref= &sjm_tab->ref; tab_ref->key= 0; /* The only temp table index. */ tab_ref->key_length= tmp_key->key_length; if (!(tab_ref->key_buff= (uchar*) thd->calloc(ALIGN_SIZE(tmp_key->key_length) * 2)) || !(tab_ref->key_copy= (store_key**) thd->alloc((sizeof(store_key*) * (tmp_key_parts + 1)))) || !(tab_ref->items= (Item**) thd->alloc(sizeof(Item*) * tmp_key_parts))) DBUG_RETURN(TRUE); /* purecov: inspected */ tab_ref->key_buff2=tab_ref->key_buff+ALIGN_SIZE(tmp_key->key_length); tab_ref->key_err=1; tab_ref->null_rejecting= 1; tab_ref->disable_cache= FALSE; KEY_PART_INFO *cur_key_part= tmp_key->key_part; store_key **ref_key= tab_ref->key_copy; uchar *cur_ref_buff= tab_ref->key_buff; for (i= 0; i < tmp_key_parts; i++, cur_key_part++, ref_key++) { tab_ref->items[i]= emb_sj_nest->sj_subq_pred->left_expr->element_index(i); int null_count= test(cur_key_part->field->real_maybe_null()); *ref_key= new store_key_item(thd, cur_key_part->field, /* TODO: the NULL byte is taken into account in cur_key_part->store_length, so instead of cur_ref_buff + test(maybe_null), we could use that information instead. */ cur_ref_buff + null_count, null_count ? cur_ref_buff : 0, cur_key_part->length, tab_ref->items[i], FALSE); cur_ref_buff+= cur_key_part->store_length; } *ref_key= NULL; /* End marker. */ /* We don't ever have guarded conditions for SJM tables, but code at SQL layer depends on cond_guards array being alloced. */ if (!(tab_ref->cond_guards= (bool**) thd->calloc(sizeof(uint*)*tmp_key_parts))) { DBUG_RETURN(TRUE); } tab_ref->key_err= 1; tab_ref->key_parts= tmp_key_parts; sjm->tab_ref= tab_ref; /* Remove the injected semi-join IN-equalities from join_tab conds. This needs to be done because the IN-equalities refer to columns of sj-inner tables which are not available after the materialization has been finished. */ for (i= 0; i < sjm->tables; i++) { remove_sj_conds(&tab[i].select_cond); if (tab[i].select) remove_sj_conds(&tab[i].select->cond); } if (!(sjm->in_equality= create_subq_in_equalities(thd, sjm, emb_sj_nest->sj_subq_pred))) DBUG_RETURN(TRUE); /* purecov: inspected */ sjm_tab->type= JT_EQ_REF; sjm_tab->select_cond= sjm->in_equality; } else { /* We'll be doing full scan of the temptable. Setup copying of temptable columns back to the record buffers for their source tables. We need this because IN-equalities refer to the original tables. EXAMPLE Consider the query: SELECT * FROM ot WHERE ot.col1 IN (SELECT it.col2 FROM it) Suppose it's executed with SJ-Materialization-scan. We choose to do scan if we can't do the lookup, i.e. the join order is (it, ot). The plan would look as follows: table access method condition it materialize+scan - ot (whatever) ot1.col1=it.col2 (C2) The condition C2 refers to current row of table it. The problem is that by the time we evaluate C2, we would have finished with scanning it itself and will be scanning the temptable. At the moment, our solution is to copy back: when we get the next temptable record, we copy its columns to their corresponding columns in the record buffers for the source tables. */ sjm->copy_field= new Copy_field[sjm->sjm_table_cols.elements]; //it.rewind(); Item **p_item= emb_sj_nest->sj_subq_pred->unit->first_select()->ref_pointer_array; for (uint i=0; i < sjm->sjm_table_cols.elements; i++) { bool dummy; Item_equal *item_eq; //Item *item= (it++)->real_item(); Item *item= (*(p_item++))->real_item(); DBUG_ASSERT(item->type() == Item::FIELD_ITEM); Field *copy_to= ((Item_field*)item)->field; /* Tricks with Item_equal are due to the following: suppose we have a query: ... WHERE cond(ot.col) AND ot.col IN (SELECT it2.col FROM it1,it2 WHERE it1.col= it2.col) then equality propagation will create an Item_equal(it1.col, it2.col, ot.col) then substitute_for_best_equal_field() will change the conditions according to the join order: table | attached condition ------+-------------------- it1 | it2 | it1.col=it2.col ot | cond(it1.col) although we've originally had "SELECT it2.col", conditions attached to subsequent outer tables will refer to it1.col, so SJM-Scan will need to unpack data to there. That is, if an element from subquery's select list participates in equality propagation, then we need to unpack it to the first element equality propagation member that refers to table that is within the subquery. */ item_eq= find_item_equal(tab->join->cond_equal, copy_to, &dummy); if (item_eq) { List_iterator it(item_eq->equal_items); /* We're interested in field items only */ if (item_eq->get_const()) it++; Item *item; while ((item= it++)) { if (!(item->used_tables() & ~emb_sj_nest->sj_inner_tables)) { DBUG_ASSERT(item->real_item()->type() == Item::FIELD_ITEM); copy_to= ((Item_field *) (item->real_item()))->field; break; } } } sjm->copy_field[i].set(copy_to, sjm->table->field[i], FALSE); /* The write_set for source tables must be set up to allow the copying */ bitmap_set_bit(copy_to->table->write_set, copy_to->field_index); } sjm_tab->type= JT_ALL; /* Initialize full scan */ sjm_tab->read_first_record= join_read_record_no_init; sjm_tab->read_record.copy_field= sjm->copy_field; sjm_tab->read_record.copy_field_end= sjm->copy_field + sjm->sjm_table_cols.elements; sjm_tab->read_record.read_record= rr_sequential_and_unpack; } sjm_tab->bush_children->end[-1].next_select= end_sj_materialize; DBUG_RETURN(FALSE); } /* Create subquery IN-equalities assuming use of materialization strategy SYNOPSIS create_subq_in_equalities() thd Thread handle sjm Semi-join materialization structure subq_pred The subquery predicate DESCRIPTION Create subquery IN-equality predicates. That is, for a subquery (oe1, oe2, ...) IN (SELECT ie1, ie2, ... FROM ...) create "oe1=ie1 AND ie1=ie2 AND ..." expression, such that ie1, ie2, .. refer to the columns of the table that's used to materialize the subquery. RETURN Created condition */ static Item *create_subq_in_equalities(THD *thd, SJ_MATERIALIZATION_INFO *sjm, Item_in_subselect *subq_pred) { Item *res= NULL; if (subq_pred->left_expr->cols() == 1) { if (!(res= new Item_func_eq(subq_pred->left_expr, new Item_field(sjm->table->field[0])))) return NULL; /* purecov: inspected */ } else { Item *conj; for (uint i= 0; i < subq_pred->left_expr->cols(); i++) { if (!(conj= new Item_func_eq(subq_pred->left_expr->element_index(i), new Item_field(sjm->table->field[i]))) || !(res= and_items(res, conj))) return NULL; /* purecov: inspected */ } } if (res->fix_fields(thd, &res)) return NULL; /* purecov: inspected */ return res; } static void remove_sj_conds(Item **tree) { if (*tree) { if (is_cond_sj_in_equality(*tree)) { *tree= NULL; return; } else if ((*tree)->type() == Item::COND_ITEM) { Item *item; List_iterator li(*(((Item_cond*)*tree)->argument_list())); while ((item= li++)) { if (is_cond_sj_in_equality(item)) li.replace(new Item_int(1)); } } } } /* Check if given Item was injected by semi-join equality */ static bool is_cond_sj_in_equality(Item *item) { if (item->type() == Item::FUNC_ITEM && ((Item_func*)item)->functype()== Item_func::EQ_FUNC) { Item_func_eq *item_eq= (Item_func_eq*)item; return test(item_eq->in_equality_no != UINT_MAX); } return FALSE; } /* Create a temporary table to weed out duplicate rowid combinations SYNOPSIS create_duplicate_weedout_tmp_table() thd Thread handle uniq_tuple_length_arg Length of the table's column sjtbl Update sjtbl->[start_]recinfo values which will be needed if we'll need to convert the created temptable from HEAP to MyISAM/Maria. DESCRIPTION Create a temporary table to weed out duplicate rowid combinations. The table has a single column that is a concatenation of all rowids in the combination. Depending on the needed length, there are two cases: 1. When the length of the column < max_key_length: CREATE TABLE tmp (col VARBINARY(n) NOT NULL, UNIQUE KEY(col)); 2. Otherwise (not a valid SQL syntax but internally supported): CREATE TABLE tmp (col VARBINARY NOT NULL, UNIQUE CONSTRAINT(col)); The code in this function was produced by extraction of relevant parts from create_tmp_table(). RETURN created table NULL on error */ TABLE *create_duplicate_weedout_tmp_table(THD *thd, uint uniq_tuple_length_arg, SJ_TMP_TABLE *sjtbl) { MEM_ROOT *mem_root_save, own_root; TABLE *table; TABLE_SHARE *share; uint temp_pool_slot=MY_BIT_NONE; char *tmpname,path[FN_REFLEN]; Field **reg_field; KEY_PART_INFO *key_part_info; KEY *keyinfo; uchar *group_buff; uchar *bitmaps; uint *blob_field; ENGINE_COLUMNDEF *recinfo, *start_recinfo; bool using_unique_constraint=FALSE; bool use_packed_rows= FALSE; Field *field, *key_field; uint null_pack_length, null_count; uchar *null_flags; uchar *pos; DBUG_ENTER("create_duplicate_weedout_tmp_table"); DBUG_ASSERT(!sjtbl->is_degenerate); /* STEP 1: Get temporary table name */ statistic_increment(thd->status_var.created_tmp_tables, &LOCK_status); if (use_temp_pool && !(test_flags & TEST_KEEP_TMP_TABLES)) temp_pool_slot = bitmap_lock_set_next(&temp_pool); if (temp_pool_slot != MY_BIT_NONE) // we got a slot sprintf(path, "%s_%lx_%i", tmp_file_prefix, current_pid, temp_pool_slot); else { /* if we run out of slots or we are not using tempool */ sprintf(path,"%s%lx_%lx_%x", tmp_file_prefix,current_pid, thd->thread_id, thd->tmp_table++); } fn_format(path, path, mysql_tmpdir, "", MY_REPLACE_EXT|MY_UNPACK_FILENAME); /* STEP 2: Figure if we'll be using a key or blob+constraint */ if (uniq_tuple_length_arg >= CONVERT_IF_BIGGER_TO_BLOB) using_unique_constraint= TRUE; /* STEP 3: Allocate memory for temptable description */ init_sql_alloc(&own_root, TABLE_ALLOC_BLOCK_SIZE, 0); if (!multi_alloc_root(&own_root, &table, sizeof(*table), &share, sizeof(*share), ®_field, sizeof(Field*) * (1+1), &blob_field, sizeof(uint)*2, &keyinfo, sizeof(*keyinfo), &key_part_info, sizeof(*key_part_info) * 2, &start_recinfo, sizeof(*recinfo)*(1*2+4), &tmpname, (uint) strlen(path)+1, &group_buff, (!using_unique_constraint ? uniq_tuple_length_arg : 0), &bitmaps, bitmap_buffer_size(1)*3, NullS)) { if (temp_pool_slot != MY_BIT_NONE) bitmap_lock_clear_bit(&temp_pool, temp_pool_slot); DBUG_RETURN(NULL); } strmov(tmpname,path); /* STEP 4: Create TABLE description */ bzero((char*) table,sizeof(*table)); bzero((char*) reg_field,sizeof(Field*)*2); table->mem_root= own_root; mem_root_save= thd->mem_root; thd->mem_root= &table->mem_root; table->field=reg_field; table->alias.set("weedout-tmp", sizeof("weedout-tmp")-1, table_alias_charset); table->reginfo.lock_type=TL_WRITE; /* Will be updated */ table->db_stat=HA_OPEN_KEYFILE+HA_OPEN_RNDFILE; table->map=1; table->temp_pool_slot = temp_pool_slot; table->copy_blobs= 1; table->in_use= thd; table->quick_keys.init(); table->covering_keys.init(); table->keys_in_use_for_query.init(); table->s= share; init_tmp_table_share(thd, share, "", 0, tmpname, tmpname); share->blob_field= blob_field; share->blob_ptr_size= portable_sizeof_char_ptr; share->table_charset= NULL; share->primary_key= MAX_KEY; // Indicate no primary key share->keys_for_keyread.init(); share->keys_in_use.init(); /* Create the field */ { /* For the sake of uniformity, always use Field_varstring (altough we could use Field_string for shorter keys) */ field= new Field_varstring(uniq_tuple_length_arg, FALSE, "rowids", share, &my_charset_bin); if (!field) DBUG_RETURN(0); field->table= table; field->key_start.init(0); field->part_of_key.init(0); field->part_of_sortkey.init(0); field->unireg_check= Field::NONE; field->flags= (NOT_NULL_FLAG | BINARY_FLAG | NO_DEFAULT_VALUE_FLAG); field->reset_fields(); field->init(table); field->orig_table= NULL; field->field_index= 0; *(reg_field++)= field; *blob_field= 0; *reg_field= 0; share->fields= 1; share->blob_fields= 0; } uint reclength= field->pack_length(); if (using_unique_constraint) { share->db_plugin= ha_lock_engine(0, TMP_ENGINE_HTON); table->file= get_new_handler(share, &table->mem_root, share->db_type()); DBUG_ASSERT(uniq_tuple_length_arg <= table->file->max_key_length()); } else { share->db_plugin= ha_lock_engine(0, heap_hton); table->file= get_new_handler(share, &table->mem_root, share->db_type()); } if (!table->file) goto err; null_count=1; null_pack_length= 1; reclength += null_pack_length; share->reclength= reclength; { uint alloc_length=ALIGN_SIZE(share->reclength + MI_UNIQUE_HASH_LENGTH+1); share->rec_buff_length= alloc_length; if (!(table->record[0]= (uchar*) alloc_root(&table->mem_root, alloc_length*3))) goto err; table->record[1]= table->record[0]+alloc_length; share->default_values= table->record[1]+alloc_length; } setup_tmp_table_column_bitmaps(table, bitmaps); recinfo= start_recinfo; null_flags=(uchar*) table->record[0]; pos=table->record[0]+ null_pack_length; if (null_pack_length) { bzero((uchar*) recinfo,sizeof(*recinfo)); recinfo->type=FIELD_NORMAL; recinfo->length=null_pack_length; recinfo++; bfill(null_flags,null_pack_length,255); // Set null fields table->null_flags= (uchar*) table->record[0]; share->null_fields= null_count; share->null_bytes= null_pack_length; } null_count=1; { //Field *field= *reg_field; uint length; bzero((uchar*) recinfo,sizeof(*recinfo)); field->move_field(pos,(uchar*) 0,0); field->reset(); /* Test if there is a default field value. The test for ->ptr is to skip 'offset' fields generated by initalize_tables */ // Initialize the table field: bzero(field->ptr, field->pack_length()); length=field->pack_length(); pos+= length; /* Make entry for create table */ recinfo->length=length; if (field->flags & BLOB_FLAG) recinfo->type= FIELD_BLOB; else if (use_packed_rows && field->real_type() == MYSQL_TYPE_STRING && length >= MIN_STRING_LENGTH_TO_PACK_ROWS) recinfo->type=FIELD_SKIP_ENDSPACE; else recinfo->type=FIELD_NORMAL; field->set_table_name(&table->alias); } if (thd->variables.tmp_table_size == ~ (ulonglong) 0) // No limit share->max_rows= ~(ha_rows) 0; else share->max_rows= (ha_rows) (((share->db_type() == heap_hton) ? min(thd->variables.tmp_table_size, thd->variables.max_heap_table_size) : thd->variables.tmp_table_size) / share->reclength); set_if_bigger(share->max_rows,1); // For dummy start options //// keyinfo= param->keyinfo; if (TRUE) { DBUG_PRINT("info",("Creating group key in temporary table")); share->keys=1; share->uniques= test(using_unique_constraint); table->key_info=keyinfo; keyinfo->key_part=key_part_info; keyinfo->flags=HA_NOSAME; keyinfo->usable_key_parts= keyinfo->key_parts= 1; keyinfo->key_length=0; keyinfo->rec_per_key=0; keyinfo->algorithm= HA_KEY_ALG_UNDEF; keyinfo->name= (char*) "weedout_key"; { key_part_info->null_bit=0; key_part_info->field= field; key_part_info->offset= field->offset(table->record[0]); key_part_info->length= (uint16) field->key_length(); key_part_info->type= (uint8) field->key_type(); key_part_info->key_type = FIELDFLAG_BINARY; if (!using_unique_constraint) { if (!(key_field= field->new_key_field(thd->mem_root, table, group_buff, field->null_ptr, field->null_bit))) goto err; key_part_info->key_part_flag|= HA_END_SPACE_ARE_EQUAL; //todo need this? } keyinfo->key_length+= key_part_info->length; } } if (thd->is_fatal_error) // If end of memory goto err; share->db_record_offset= 1; table->no_rows= 1; // We don't need the data // recinfo must point after last field recinfo++; if (share->db_type() == TMP_ENGINE_HTON) { if (create_internal_tmp_table(table, keyinfo, start_recinfo, &recinfo, 0, 0)) goto err; } sjtbl->start_recinfo= start_recinfo; sjtbl->recinfo= recinfo; if (open_tmp_table(table)) goto err; thd->mem_root= mem_root_save; DBUG_RETURN(table); err: thd->mem_root= mem_root_save; free_tmp_table(thd,table); /* purecov: inspected */ if (temp_pool_slot != MY_BIT_NONE) bitmap_lock_clear_bit(&temp_pool, temp_pool_slot); DBUG_RETURN(NULL); /* purecov: inspected */ } /* SemiJoinDuplicateElimination: Reset the temporary table */ int do_sj_reset(SJ_TMP_TABLE *sj_tbl) { DBUG_ENTER("do_sj_reset"); if (sj_tbl->tmp_table) { int rc= sj_tbl->tmp_table->file->ha_delete_all_rows(); DBUG_RETURN(rc); } sj_tbl->have_degenerate_row= FALSE; DBUG_RETURN(0); } /* SemiJoinDuplicateElimination: Weed out duplicate row combinations SYNPOSIS do_sj_dups_weedout() thd Thread handle sjtbl Duplicate weedout table DESCRIPTION Try storing current record combination of outer tables (i.e. their rowids) in the temporary table. This records the fact that we've seen this record combination and also tells us if we've seen it before. RETURN -1 Error 1 The row combination is a duplicate (discard it) 0 The row combination is not a duplicate (continue) */ int do_sj_dups_weedout(THD *thd, SJ_TMP_TABLE *sjtbl) { int error; SJ_TMP_TABLE::TAB *tab= sjtbl->tabs; SJ_TMP_TABLE::TAB *tab_end= sjtbl->tabs_end; uchar *ptr; uchar *nulls_ptr; DBUG_ENTER("do_sj_dups_weedout"); if (sjtbl->is_degenerate) { if (sjtbl->have_degenerate_row) DBUG_RETURN(1); sjtbl->have_degenerate_row= TRUE; DBUG_RETURN(0); } ptr= sjtbl->tmp_table->record[0] + 1; /* Put the the rowids tuple into table->record[0]: */ // 1. Store the length if (((Field_varstring*)(sjtbl->tmp_table->field[0]))->length_bytes == 1) { *ptr= (uchar)(sjtbl->rowid_len + sjtbl->null_bytes); ptr++; } else { int2store(ptr, sjtbl->rowid_len + sjtbl->null_bytes); ptr += 2; } nulls_ptr= ptr; // 2. Zero the null bytes if (sjtbl->null_bytes) { bzero(ptr, sjtbl->null_bytes); ptr += sjtbl->null_bytes; } // 3. Put the rowids for (uint i=0; tab != tab_end; tab++, i++) { handler *h= tab->join_tab->table->file; if (tab->join_tab->table->maybe_null && tab->join_tab->table->null_row) { /* It's a NULL-complemented row */ *(nulls_ptr + tab->null_byte) |= tab->null_bit; bzero(ptr + tab->rowid_offset, h->ref_length); } else { /* Copy the rowid value */ memcpy(ptr + tab->rowid_offset, h->ref, h->ref_length); } } error= sjtbl->tmp_table->file->ha_write_tmp_row(sjtbl->tmp_table->record[0]); if (error) { /* create_internal_tmp_table_from_heap will generate error if needed */ if (!sjtbl->tmp_table->file->is_fatal_error(error, HA_CHECK_DUP)) DBUG_RETURN(1); /* Duplicate */ if (create_internal_tmp_table_from_heap(thd, sjtbl->tmp_table, sjtbl->start_recinfo, &sjtbl->recinfo, error, 1)) DBUG_RETURN(-1); } DBUG_RETURN(0); } /* Setup the strategies to eliminate semi-join duplicates. SYNOPSIS setup_semijoin_dups_elimination() join Join to process options Join options (needed to see if join buffering will be used or not) no_jbuf_after Another bit of information re where join buffering will be used. DESCRIPTION Setup the strategies to eliminate semi-join duplicates. ATM there are 4 strategies: 1. DuplicateWeedout (use of temptable to remove duplicates based on rowids of row combinations) 2. FirstMatch (pick only the 1st matching row combination of inner tables) 3. LooseScan (scanning the sj-inner table in a way that groups duplicates together and picking the 1st one) 4. SJ-Materialization. The join order has "duplicate-generating ranges", and every range is served by one strategy or a combination of FirstMatch with with some other strategy. "Duplicate-generating range" is defined as a range within the join order that contains all of the inner tables of a semi-join. All ranges must be disjoint, if tables of several semi-joins are interleaved, then the ranges are joined together, which is equivalent to converting SELECT ... WHERE oe1 IN (SELECT ie1 ...) AND oe2 IN (SELECT ie2 ) to SELECT ... WHERE (oe1, oe2) IN (SELECT ie1, ie2 ... ...) . Applicability conditions are as follows: DuplicateWeedout strategy ~~~~~~~~~~~~~~~~~~~~~~~~~ (ot|nt)* [ it ((it|ot|nt)* (it|ot))] (nt)* +------+ +=========================+ +---+ (1) (2) (3) (1) - Prefix of OuterTables (those that participate in IN-equality and/or are correlated with subquery) and outer Non-correlated tables. (2) - The handled range. The range starts with the first sj-inner table, and covers all sj-inner and outer tables Within the range, Inner, Outer, outer non-correlated tables may follow in any order. (3) - The suffix of outer non-correlated tables. FirstMatch strategy ~~~~~~~~~~~~~~~~~~~ (ot|nt)* [ it ((it|nt)* it) ] (nt)* +------+ +==================+ +---+ (1) (2) (3) (1) - Prefix of outer and non-correlated tables (2) - The handled range, which may contain only inner and non-correlated tables. (3) - The suffix of outer non-correlated tables. LooseScan strategy ~~~~~~~~~~~~~~~~~~ (ot|ct|nt) [ loosescan_tbl (ot|nt|it)* it ] (ot|nt)* +--------+ +===========+ +=============+ +------+ (1) (2) (3) (4) (1) - Prefix that may contain any outer tables. The prefix must contain all the non-trivially correlated outer tables. (non-trivially means that the correlation is not just through the IN-equality). (2) - Inner table for which the LooseScan scan is performed. (3) - The remainder of the duplicate-generating range. It is served by application of FirstMatch strategy, with the exception that outer IN-correlated tables are considered to be non-correlated. (4) - THe suffix of outer and outer non-correlated tables. The choice between the strategies is made by the join optimizer (see advance_sj_state() and fix_semijoin_strategies_for_picked_join_order()). This function sets up all fields/structures/etc needed for execution except for setup/initialization of semi-join materialization which is done in setup_sj_materialization() (todo: can't we move that to here also?) RETURN FALSE OK TRUE Out of memory error */ int setup_semijoin_dups_elimination(JOIN *join, ulonglong options, uint no_jbuf_after) { uint i; THD *thd= join->thd; DBUG_ENTER("setup_semijoin_dups_elimination"); POSITION *pos= join->best_positions + join->const_tables; for (i= join->const_tables ; i < join->top_join_tab_count; ) { JOIN_TAB *tab=join->join_tab + i; //POSITION *pos= join->best_positions + i; uint keylen, keyno; switch (pos->sj_strategy) { case SJ_OPT_MATERIALIZE: case SJ_OPT_MATERIALIZE_SCAN: /* Do nothing */ i+= 1;// It used to be pos->n_sj_tables, but now they are embedded in a nest pos += pos->n_sj_tables; break; case SJ_OPT_LOOSE_SCAN: { /* We jump from the last table to the first one */ tab->loosescan_match_tab= tab + pos->n_sj_tables - 1; for (uint j= i; j < i + pos->n_sj_tables; j++) join->join_tab[j].inside_loosescan_range= TRUE; /* Calculate key length */ keylen= 0; keyno= pos->loosescan_key; for (uint kp=0; kp < pos->loosescan_parts; kp++) keylen += tab->table->key_info[keyno].key_part[kp].store_length; tab->loosescan_key_len= keylen; if (pos->n_sj_tables > 1) tab[pos->n_sj_tables - 1].do_firstmatch= tab; i+= pos->n_sj_tables; pos+= pos->n_sj_tables; break; } case SJ_OPT_DUPS_WEEDOUT: { /* Check for join buffering. If there is one, move the first table forwards, but do not destroy other duplicate elimination methods. */ uint first_table= i; uint join_cache_level= join->thd->variables.join_cache_level; for (uint j= i; j < i + pos->n_sj_tables; j++) { /* When we'll properly take join buffering into account during join optimization, the below check should be changed to "if (join->best_positions[j].use_join_buffer && j <= no_jbuf_after)". For now, use a rough criteria: */ JOIN_TAB *js_tab=join->join_tab + j; if (j != join->const_tables && js_tab->use_quick != 2 && j <= no_jbuf_after && ((js_tab->type == JT_ALL && join_cache_level != 0) || (join_cache_level > 2 && (js_tab->type == JT_REF || js_tab->type == JT_EQ_REF)))) { /* Looks like we'll be using join buffer */ first_table= join->const_tables; break; } } SJ_TMP_TABLE::TAB sjtabs[MAX_TABLES]; SJ_TMP_TABLE::TAB *last_tab= sjtabs; uint jt_rowid_offset= 0; // # tuple bytes are already occupied (w/o NULL bytes) uint jt_null_bits= 0; // # null bits in tuple bytes /* Walk through the range and remember - tables that need their rowids to be put into temptable - the last outer table */ for (JOIN_TAB *j=join->join_tab + first_table; j < join->join_tab + i + pos->n_sj_tables; j++) { if (sj_table_is_included(join, j)) { last_tab->join_tab= j; last_tab->rowid_offset= jt_rowid_offset; jt_rowid_offset += j->table->file->ref_length; if (j->table->maybe_null) { last_tab->null_byte= jt_null_bits / 8; last_tab->null_bit= jt_null_bits++; } last_tab++; j->table->prepare_for_position(); j->keep_current_rowid= TRUE; } } SJ_TMP_TABLE *sjtbl; if (jt_rowid_offset) /* Temptable has at least one rowid */ { size_t tabs_size= (last_tab - sjtabs) * sizeof(SJ_TMP_TABLE::TAB); if (!(sjtbl= (SJ_TMP_TABLE*)thd->alloc(sizeof(SJ_TMP_TABLE))) || !(sjtbl->tabs= (SJ_TMP_TABLE::TAB*) thd->alloc(tabs_size))) DBUG_RETURN(TRUE); /* purecov: inspected */ memcpy(sjtbl->tabs, sjtabs, tabs_size); sjtbl->is_degenerate= FALSE; sjtbl->tabs_end= sjtbl->tabs + (last_tab - sjtabs); sjtbl->rowid_len= jt_rowid_offset; sjtbl->null_bits= jt_null_bits; sjtbl->null_bytes= (jt_null_bits + 7)/8; sjtbl->tmp_table= create_duplicate_weedout_tmp_table(thd, sjtbl->rowid_len + sjtbl->null_bytes, sjtbl); join->sj_tmp_tables.push_back(sjtbl->tmp_table); } else { /* This is a special case where the entire subquery predicate does not depend on anything at all, ie this is WHERE const IN (uncorrelated select) */ if (!(sjtbl= (SJ_TMP_TABLE*)thd->alloc(sizeof(SJ_TMP_TABLE)))) DBUG_RETURN(TRUE); /* purecov: inspected */ sjtbl->tmp_table= NULL; sjtbl->is_degenerate= TRUE; sjtbl->have_degenerate_row= FALSE; } join->join_tab[first_table].flush_weedout_table= sjtbl; join->join_tab[i + pos->n_sj_tables - 1].check_weed_out_table= sjtbl; i+= pos->n_sj_tables; pos+= pos->n_sj_tables; break; } case SJ_OPT_FIRST_MATCH: { JOIN_TAB *j, *jump_to= tab-1; for (j= tab; j != tab + pos->n_sj_tables; j++) { /* NOTE: this loop probably doesn't do the right thing for the case where FirstMatch's duplicate-generating range is interleaved with "unrelated" tables (as specified in WL#3750, section 2.2). */ if (!j->emb_sj_nest) jump_to= tab; else { j->first_sj_inner_tab= tab; j->last_sj_inner_tab= tab + pos->n_sj_tables - 1; } } j[-1].do_firstmatch= jump_to; i+= pos->n_sj_tables; pos+= pos->n_sj_tables; break; } case SJ_OPT_NONE: i++; pos++; break; } } DBUG_RETURN(FALSE); } /* Destroy all temporary tables created by NL-semijoin runtime */ void destroy_sj_tmp_tables(JOIN *join) { List_iterator it(join->sj_tmp_tables); TABLE *table; while ((table= it++)) { /* SJ-Materialization tables are initialized for either sequential reading or index lookup, DuplicateWeedout tables are not initialized for read (we only write to them), so need to call ha_index_or_rnd_end. */ table->file->ha_index_or_rnd_end(); free_tmp_table(join->thd, table); } join->sj_tmp_tables.empty(); join->sjm_info_list.empty(); } /* Remove all records from all temp tables used by NL-semijoin runtime SYNOPSIS clear_sj_tmp_tables() join The join to remove tables for DESCRIPTION Remove all records from all temp tables used by NL-semijoin runtime. This must be done before every join re-execution. */ int clear_sj_tmp_tables(JOIN *join) { int res; List_iterator
it(join->sj_tmp_tables); TABLE *table; while ((table= it++)) { if ((res= table->file->ha_delete_all_rows())) return res; /* purecov: inspected */ } SJ_MATERIALIZATION_INFO *sjm; List_iterator it2(join->sjm_info_list); while ((sjm= it2++)) { sjm->materialized= FALSE; } return 0; } /* Check if the table's rowid is included in the temptable SYNOPSIS sj_table_is_included() join The join join_tab The table to be checked DESCRIPTION SemiJoinDuplicateElimination: check the table's rowid should be included in the temptable. This is so if 1. The table is not embedded within some semi-join nest 2. The has been pulled out of a semi-join nest, or 3. The table is functionally dependent on some previous table [4. This is also true for constant tables that can't be NULL-complemented but this function is not called for such tables] RETURN TRUE - Include table's rowid FALSE - Don't */ static bool sj_table_is_included(JOIN *join, JOIN_TAB *join_tab) { if (join_tab->emb_sj_nest) return FALSE; /* Check if this table is functionally dependent on the tables that are within the same outer join nest */ TABLE_LIST *embedding= join_tab->table->pos_in_table_list->embedding; if (join_tab->type == JT_EQ_REF) { table_map depends_on= 0; uint idx; for (uint kp= 0; kp < join_tab->ref.key_parts; kp++) depends_on |= join_tab->ref.items[kp]->used_tables(); Table_map_iterator it(depends_on & ~PSEUDO_TABLE_BITS); while ((idx= it.next_bit())!=Table_map_iterator::BITMAP_END) { JOIN_TAB *ref_tab= join->map2table[idx]; if (embedding != ref_tab->table->pos_in_table_list->embedding) return TRUE; } /* Ok, functionally dependent */ return FALSE; } /* Not functionally dependent => need to include*/ return TRUE; } /* Index lookup-based subquery: save some flags for EXPLAIN output SYNOPSIS save_index_subquery_explain_info() join_tab Subquery's join tab (there is only one as index lookup is only used for subqueries that are single-table SELECTs) where Subquery's WHERE clause DESCRIPTION For index lookup-based subquery (i.e. one executed with subselect_uniquesubquery_engine or subselect_indexsubquery_engine), check its EXPLAIN output row should contain "Using index" (TAB_INFO_FULL_SCAN_ON_NULL) "Using Where" (TAB_INFO_USING_WHERE) "Full scan on NULL key" (TAB_INFO_FULL_SCAN_ON_NULL) and set appropriate flags in join_tab->packed_info. */ static void save_index_subquery_explain_info(JOIN_TAB *join_tab, Item* where) { join_tab->packed_info= TAB_INFO_HAVE_VALUE; if (join_tab->table->covering_keys.is_set(join_tab->ref.key)) join_tab->packed_info |= TAB_INFO_USING_INDEX; if (where) join_tab->packed_info |= TAB_INFO_USING_WHERE; for (uint i = 0; i < join_tab->ref.key_parts; i++) { if (join_tab->ref.cond_guards[i]) { join_tab->packed_info |= TAB_INFO_FULL_SCAN_ON_NULL; break; } } } /* Check if the join can be rewritten to [unique_]indexsubquery_engine DESCRIPTION Check if the join can be changed into [unique_]indexsubquery_engine. The check is done after join optimization, the idea is that if the join has only one table and uses a [eq_]ref access generated from subselect's IN-equality then we replace it with a subselect_indexsubquery_engine or a subselect_uniquesubquery_engine. RETURN 0 - Ok, rewrite done (stop join optimization and return) 1 - Fatal error (stop join optimization and return) -1 - No rewrite performed, continue with join optimization */ int rewrite_to_index_subquery_engine(JOIN *join) { THD *thd= join->thd; JOIN_TAB* join_tab=join->join_tab; SELECT_LEX_UNIT *unit= join->unit; DBUG_ENTER("rewrite_to_index_subquery_engine"); /* is this simple IN subquery? */ /* TODO: In order to use these more efficient subquery engines in more cases, the following problems need to be solved: - the code that removes GROUP BY (group_list), also adds an ORDER BY (order), thus GROUP BY queries (almost?) never pass through this branch. Solution: remove the test below '!join->order', because we remove the ORDER clase for subqueries anyway. - in order to set a more efficient engine, the optimizer needs to both decide to remove GROUP BY, *and* select one of the JT_[EQ_]REF[_OR_NULL] access methods, *and* loose scan should be more expensive or inapliccable. When is that possible? - Consider expanding the applicability of this rewrite for loose scan for group by queries. */ if (!join->group_list && !join->order && join->unit->item && join->unit->item->substype() == Item_subselect::IN_SUBS && join->table_count == 1 && join->conds && !join->unit->is_union()) { if (!join->having) { Item *where= join->conds; if (join_tab[0].type == JT_EQ_REF && join_tab[0].ref.items[0]->name == in_left_expr_name) { remove_subq_pushed_predicates(join, &where); save_index_subquery_explain_info(join_tab, where); join_tab[0].type= JT_UNIQUE_SUBQUERY; join->error= 0; DBUG_RETURN(unit->item-> change_engine(new subselect_uniquesubquery_engine(thd, join_tab, unit->item, where))); } else if (join_tab[0].type == JT_REF && join_tab[0].ref.items[0]->name == in_left_expr_name) { remove_subq_pushed_predicates(join, &where); save_index_subquery_explain_info(join_tab, where); join_tab[0].type= JT_INDEX_SUBQUERY; join->error= 0; DBUG_RETURN(unit->item-> change_engine(new subselect_indexsubquery_engine(thd, join_tab, unit->item, where, NULL, 0))); } } else if (join_tab[0].type == JT_REF_OR_NULL && join_tab[0].ref.items[0]->name == in_left_expr_name && join->having->name == in_having_cond) { join_tab[0].type= JT_INDEX_SUBQUERY; join->error= 0; join->conds= remove_additional_cond(join->conds); save_index_subquery_explain_info(join_tab, join->conds); DBUG_RETURN(unit->item-> change_engine(new subselect_indexsubquery_engine(thd, join_tab, unit->item, join->conds, join->having, 1))); } } DBUG_RETURN(-1); /* Haven't done the rewrite */ } /** Remove additional condition inserted by IN/ALL/ANY transformation. @param conds condition for processing @return new conditions */ static Item *remove_additional_cond(Item* conds) { if (conds->name == in_additional_cond) return 0; if (conds->type() == Item::COND_ITEM) { Item_cond *cnd= (Item_cond*) conds; List_iterator li(*(cnd->argument_list())); Item *item; while ((item= li++)) { if (item->name == in_additional_cond) { li.remove(); if (cnd->argument_list()->elements == 1) return cnd->argument_list()->head(); return conds; } } } return conds; } /* Remove the predicates pushed down into the subquery SYNOPSIS remove_subq_pushed_predicates() where IN Must be NULL OUT The remaining WHERE condition, or NULL DESCRIPTION Given that this join will be executed using (unique|index)_subquery, without "checking NULL", remove the predicates that were pushed down into the subquery. If the subquery compares scalar values, we can remove the condition that was wrapped into trig_cond (it will be checked when needed by the subquery engine) If the subquery compares row values, we need to keep the wrapped equalities in the WHERE clause: when the left (outer) tuple has both NULL and non-NULL values, we'll do a full table scan and will rely on the equalities corresponding to non-NULL parts of left tuple to filter out non-matching records. TODO: We can remove the equalities that will be guaranteed to be true by the fact that subquery engine will be using index lookup. This must be done only for cases where there are no conversion errors of significance, e.g. 257 that is searched in a byte. But this requires homogenization of the return codes of all Field*::store() methods. */ static void remove_subq_pushed_predicates(JOIN *join, Item **where) { if (join->conds->type() == Item::FUNC_ITEM && ((Item_func *)join->conds)->functype() == Item_func::EQ_FUNC && ((Item_func *)join->conds)->arguments()[0]->type() == Item::REF_ITEM && ((Item_func *)join->conds)->arguments()[1]->type() == Item::FIELD_ITEM && test_if_ref (join->conds, (Item_field *)((Item_func *)join->conds)->arguments()[1], ((Item_func *)join->conds)->arguments()[0])) { *where= 0; return; } } /** Optimize all subqueries of a query that were not flattened into a semijoin. @details Optimize all immediate children subqueries of a query. This phase must be called after substitute_for_best_equal_field() because that function may replace items with other items from a multiple equality, and we need to reference the correct items in the index access method of the IN predicate. @return Operation status @retval FALSE success. @retval TRUE error occurred. */ bool JOIN::optimize_unflattened_subqueries() { return select_lex->optimize_unflattened_subqueries(); } /* Join tab execution startup function. SYNOPSIS join_tab_execution_startup() tab Join tab to perform startup actions for DESCRIPTION Join tab execution startup function. This is different from tab->read_first_record in the regard that this has actions that are to be done once per join execution. Currently there are only two possible startup functions, so we have them both here inside if (...) branches. In future we could switch to function pointers. TODO: consider moving this together with JOIN_TAB::preread_init RETURN NESTED_LOOP_OK - OK NESTED_LOOP_ERROR| NESTED_LOOP_KILLED - Error, abort the join execution */ enum_nested_loop_state join_tab_execution_startup(JOIN_TAB *tab) { Item_in_subselect *in_subs; DBUG_ENTER("join_tab_execution_startup"); if (tab->table->pos_in_table_list && (in_subs= tab->table->pos_in_table_list->jtbm_subselect)) { /* It's a non-merged SJM nest */ DBUG_ASSERT(in_subs->engine->engine_type() == subselect_engine::HASH_SJ_ENGINE); subselect_hash_sj_engine *hash_sj_engine= ((subselect_hash_sj_engine*)in_subs->engine); if (!hash_sj_engine->is_materialized) { hash_sj_engine->materialize_join->exec(); hash_sj_engine->is_materialized= TRUE; if (hash_sj_engine->materialize_join->error || tab->join->thd->is_fatal_error) DBUG_RETURN(NESTED_LOOP_ERROR); } } else if (tab->bush_children) { /* It's a merged SJM nest */ enum_nested_loop_state rc; SJ_MATERIALIZATION_INFO *sjm= tab->bush_children->start->emb_sj_nest->sj_mat_info; if (!sjm->materialized) { JOIN *join= tab->join; JOIN_TAB *join_tab= tab->bush_children->start; JOIN_TAB *save_return_tab= join->return_tab; /* Now run the join for the inner tables. The first call is to run the join, the second one is to signal EOF (this is essential for some join strategies, e.g. it will make join buffering flush the records) */ if ((rc= sub_select(join, join_tab, FALSE/* no EOF */)) < 0 || (rc= sub_select(join, join_tab, TRUE/* now EOF */)) < 0) { join->return_tab= save_return_tab; DBUG_RETURN(rc); /* it's NESTED_LOOP_(ERROR|KILLED)*/ } join->return_tab= save_return_tab; sjm->materialized= TRUE; } } DBUG_RETURN(NESTED_LOOP_OK); } /** Choose an optimal strategy to execute an IN/ALL/ANY subquery predicate based on cost. @param join_tables the set of tables joined in the subquery @notes The method chooses between the materialization and IN=>EXISTS rewrite strategies for the execution of a non-flattened subquery IN predicate. The cost-based decision is made as follows: 1. compute materialize_strategy_cost based on the unmodified subquery 2. reoptimize the subquery taking into account the IN-EXISTS predicates 3. compute in_exists_strategy_cost based on the reoptimized plan 4. compare and set the cheaper strategy if (materialize_strategy_cost >= in_exists_strategy_cost) in_strategy = MATERIALIZATION else in_strategy = IN_TO_EXISTS 5. if in_strategy = MATERIALIZATION and it is not possible to initialize it revert to IN_TO_EXISTS 6. if (in_strategy == MATERIALIZATION) revert the subquery plan to the original one before reoptimizing else inject the IN=>EXISTS predicates into the new EXISTS subquery plan The implementation itself is a bit more complicated because it takes into account two more factors: - whether the user allowed both strategies through an optimizer_switch, and - if materialization was the cheaper strategy, whether it can be executed or not. @retval FALSE success. @retval TRUE error occurred. */ bool JOIN::choose_subquery_plan(table_map join_tables) { Join_plan_state save_qep; /* The original QEP of the subquery. */ enum_reopt_result reopt_result= REOPT_NONE; Item_in_subselect *in_subs; if (is_in_subquery()) { in_subs= (Item_in_subselect*) unit->item; if (in_subs->create_in_to_exists_cond(this)) return true; } else return false; /* A strategy must be chosen earlier. */ DBUG_ASSERT(in_subs->has_strategy()); DBUG_ASSERT(in_to_exists_where || in_to_exists_having); DBUG_ASSERT(!in_to_exists_where || in_to_exists_where->fixed); DBUG_ASSERT(!in_to_exists_having || in_to_exists_having->fixed); /* Compute and compare the costs of materialization and in-exists if both strategies are possible and allowed by the user (checked during the prepare phase. */ if (in_subs->test_strategy(SUBS_MATERIALIZATION) && in_subs->test_strategy(SUBS_IN_TO_EXISTS)) { JOIN *outer_join; JOIN *inner_join= this; /* Number of unique value combinations filtered by the IN predicate. */ double outer_lookup_keys; /* Cost and row count of the unmodified subquery. */ double inner_read_time_1, inner_record_count_1; /* Cost of the subquery with injected IN-EXISTS predicates. */ double inner_read_time_2; /* The cost to compute IN via materialization. */ double materialize_strategy_cost; /* The cost of the IN->EXISTS strategy. */ double in_exists_strategy_cost; double dummy; /* A. Estimate the number of rows of the outer table that will be filtered by the IN predicate. */ outer_join= unit->outer_select() ? unit->outer_select()->join : NULL; if (outer_join && outer_join->table_count > 0) { /* TODO: Currently outer_lookup_keys is computed as the number of rows in the partial join including the JOIN_TAB where the IN predicate is pushed to. In the general case this is a gross overestimate because due to caching we are interested only in the number of unique keys. The search key may be formed by columns from much fewer than all tables in the partial join. Example: select * from t1, t2 where t1.c1 = t2.key AND t2.c2 IN (select ...); If the join order: t1, t2, the number of unique lookup keys is ~ to the number of unique values t2.c2 in the partial join t1 join t2. */ outer_join->get_partial_cost_and_fanout(in_subs->get_join_tab_idx(), table_map(-1), &dummy, &outer_lookup_keys); } else { /* TODO: outer_join can be NULL for DELETE statements. How to compute its cost? */ outer_lookup_keys= 1; } /* B. Estimate the cost and number of records of the subquery both unmodified, and with injected IN->EXISTS predicates. */ inner_read_time_1= inner_join->best_read; inner_record_count_1= inner_join->record_count; if (in_to_exists_where && const_tables != table_count) { /* Re-optimize and cost the subquery taking into account the IN-EXISTS conditions. */ reopt_result= reoptimize(in_to_exists_where, join_tables, &save_qep); if (reopt_result == REOPT_ERROR) return TRUE; /* Get the cost of the modified IN-EXISTS plan. */ inner_read_time_2= inner_join->best_read; } else { /* Reoptimization would not produce any better plan. */ inner_read_time_2= inner_read_time_1; } /* C. Compute execution costs. */ /* C.1 Compute the cost of the materialization strategy. */ //uint rowlen= get_tmp_table_rec_length(unit->first_select()->item_list); uint rowlen= get_tmp_table_rec_length(ref_pointer_array, select_lex->item_list.elements); /* The cost of writing one row into the temporary table. */ double write_cost= get_tmp_table_write_cost(thd, inner_record_count_1, rowlen); /* The cost of a lookup into the unique index of the materialized table. */ double lookup_cost= get_tmp_table_lookup_cost(thd, inner_record_count_1, rowlen); /* The cost of executing the subquery and storing its result in an indexed temporary table. */ double materialization_cost= inner_read_time_1 + write_cost * inner_record_count_1; materialize_strategy_cost= materialization_cost + outer_lookup_keys * lookup_cost; /* C.2 Compute the cost of the IN=>EXISTS strategy. */ in_exists_strategy_cost= outer_lookup_keys * inner_read_time_2; /* C.3 Compare the costs and choose the cheaper strategy. */ if (materialize_strategy_cost >= in_exists_strategy_cost) in_subs->set_strategy(SUBS_IN_TO_EXISTS); else in_subs->set_strategy(SUBS_MATERIALIZATION); DBUG_PRINT("info", ("mat_strategy_cost: %.2f, mat_cost: %.2f, write_cost: %.2f, lookup_cost: %.2f", materialize_strategy_cost, materialization_cost, write_cost, lookup_cost)); DBUG_PRINT("info", ("inx_strategy_cost: %.2f, inner_read_time_2: %.2f", in_exists_strategy_cost, inner_read_time_2)); DBUG_PRINT("info",("outer_lookup_keys: %.2f", outer_lookup_keys)); } /* If (1) materialization is a possible strategy based on semantic analysis during the prepare phase, then if (2) it is more expensive than the IN->EXISTS transformation, and (3) it is not possible to create usable indexes for the materialization strategy, fall back to IN->EXISTS. otherwise use materialization. */ if (in_subs->test_strategy(SUBS_MATERIALIZATION) && in_subs->setup_mat_engine()) { /* If materialization was the cheaper or the only user-selected strategy, but it is not possible to execute it due to limitations in the implementation, fall back to IN-TO-EXISTS. */ in_subs->set_strategy(SUBS_IN_TO_EXISTS); } if (in_subs->test_strategy(SUBS_MATERIALIZATION)) { /* Restore the original query plan used for materialization. */ if (reopt_result == REOPT_NEW_PLAN) restore_query_plan(&save_qep); in_subs->unit->uncacheable&= ~UNCACHEABLE_DEPENDENT_INJECTED; select_lex->uncacheable&= ~UNCACHEABLE_DEPENDENT_INJECTED; /* Reset the "LIMIT 1" set in Item_exists_subselect::fix_length_and_dec. TODO: Currently we set the subquery LIMIT to infinity, and this is correct because we forbid at parse time LIMIT inside IN subqueries (see Item_in_subselect::test_limit). However, once we allow this, here we should set the correct limit if given in the query. */ in_subs->unit->global_parameters->select_limit= NULL; in_subs->unit->set_limit(unit->global_parameters); /* Set the limit of this JOIN object as well, because normally its being set in the beginning of JOIN::optimize, which was already done. */ select_limit= in_subs->unit->select_limit_cnt; } else if (in_subs->test_strategy(SUBS_IN_TO_EXISTS)) { if (reopt_result == REOPT_NONE && in_to_exists_where && const_tables != table_count) { /* The subquery was not reoptimized with the newly injected IN-EXISTS conditions either because the user allowed only the IN-EXISTS strategy, or because materialization was not possible based on semantic analysis. */ reopt_result= reoptimize(in_to_exists_where, join_tables, NULL); if (reopt_result == REOPT_ERROR) return TRUE; } if (in_subs->inject_in_to_exists_cond(this)) return TRUE; /* It is IN->EXISTS transformation so we should mark subquery as dependent */ in_subs->unit->uncacheable|= UNCACHEABLE_DEPENDENT_INJECTED; select_lex->uncacheable|= UNCACHEABLE_DEPENDENT_INJECTED; select_limit= 1; } else DBUG_ASSERT(FALSE); return FALSE; } /** Choose a query plan for a table-less subquery. @notes @retval FALSE success. @retval TRUE error occurred. */ bool JOIN::choose_tableless_subquery_plan() { DBUG_ASSERT(!tables_list || !table_count); if (unit->item) { DBUG_ASSERT(unit->item->type() == Item::SUBSELECT_ITEM); Item_subselect *subs_predicate= unit->item; /* If the optimizer determined that his query has an empty result, in most cases the subquery predicate is a known constant value - either FALSE or NULL. The implementation of Item_subselect::reset() determines which one. */ if (zero_result_cause) { if (!implicit_grouping) { /* Both group by queries and non-group by queries without aggregate functions produce empty subquery result. */ subs_predicate->reset(); subs_predicate->make_const(); return FALSE; } /* TODO: A further optimization is possible when a non-group query with MIN/MAX/COUNT is optimized by opt_sum_query. Then, if there are only MIN/MAX functions over an empty result set, the subquery result is a NULL value/row, thus the value of subs_predicate is NULL. */ } if (subs_predicate->is_in_predicate()) { Item_in_subselect *in_subs; in_subs= (Item_in_subselect*) subs_predicate; in_subs->set_strategy(SUBS_IN_TO_EXISTS); if (in_subs->create_in_to_exists_cond(this) || in_subs->inject_in_to_exists_cond(this)) return TRUE; tmp_having= having; } } return FALSE; }