/* Copyright (c) 2009, 2011, Monty Program Ab This program is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; version 2 of the License. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program; if not, write to the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02111-1301 USA */ /** @file @brief Table Elimination Module @defgroup Table_Elimination Table Elimination Module @{ */ #ifdef USE_PRAGMA_IMPLEMENTATION #pragma implementation // gcc: Class implementation #endif #include "my_bit.h" #include "sql_select.h" /* OVERVIEW ======== This file contains table elimination module. The idea behind table elimination is as follows: suppose we have a left join SELECT * FROM t1 LEFT JOIN (t2 JOIN t3) ON t2.primary_key=t1.col AND t2.primary_key=t2.col WHERE ... such that * columns of the inner tables are not used anywhere ouside the outer join (not in WHERE, not in GROUP/ORDER BY clause, not in select list etc etc), * inner side of the outer join is guaranteed to produce at most one matching record combination for each record combination of outer tables. then the inner side of the outer join can be removed from the query, as it will always produce only one record combination (either real or null-complemented one) and we don't care about what that record combination is. MODULE INTERFACE ================ The module has one entry point - the eliminate_tables() function, which one needs to call (once) at some point before join optimization. eliminate_tables() operates over the JOIN structures. Logically, it removes the inner tables of an outer join operation together with the operation itself. Physically, it changes the following members: * Eliminated tables are marked as constant and moved to the front of the join order. * In addition to this, they are recorded in JOIN::eliminated_tables bitmap. * Items that became disused because they were in the ON expression of an eliminated outer join are notified by means of the Item tree walk which calls Item::mark_as_eliminated_processor for every item - At the moment the only Item that cares whether it was eliminated is Item_subselect with its Item_subselect::eliminated flag which is used by EXPLAIN code to check if the subquery should be shown in EXPLAIN. Table elimination is redone on every PS re-execution. TABLE ELIMINATION ALGORITHM FOR ONE OUTER JOIN ============================================== As described above, we can remove inner side of an outer join if it is 1. not referred to from any other parts of the query 2. always produces one matching record combination. We check #1 by doing a recursive descent down the join->join_list while maintaining a union of used_tables() attribute of all Item expressions in other parts of the query. When we encounter an outer join, we check if the bitmap of tables on its inner side has intersection with tables that are used elsewhere. No intersection means that inner side of the outer join could potentially be eliminated. In order to check #2, one needs to prove that inner side of an outer join is functionally dependent on the outside. The proof is constructed from functional dependencies of intermediate objects: - Inner side of outer join is functionally dependent when each of its tables are functionally dependent. (We assume a table is functionally dependent when its dependencies allow to uniquely identify one table record, or no records). - Table is functionally dependent when it has got a unique key whose columns are functionally dependent. - A column is functionally dependent when we could locate an AND-part of a certain ON clause in form tblX.columnY= expr where expr is functionally depdendent. expr is functionally dependent when all columns that it refers to are functionally dependent. These relationships are modeled as a bipartite directed graph that has dependencies as edges and two kinds of nodes: Value nodes: - Table column values (each is a value of tblX.columnY) - Table values (each node represents a table inside the join nest we're trying to eliminate). A value has one attribute, it is either bound (i.e. functionally dependent) or not. Module nodes: - Modules representing tblX.colY=expr equalities. Equality module has = incoming edges from columns used in expr = outgoing edge to tblX.colY column. - Nodes representing unique keys. Unique key has = incoming edges from key component value modules = outgoing edge to key's table module - Inner side of outer join module. Outer join module has = incoming edges from table value modules = No outgoing edges. Once we reach it, we know we can eliminate the outer join. A module may depend on multiple values, and hence its primary attribute is the number of its arguments that are not bound. The algorithm starts with equality nodes that don't have any incoming edges (their expressions are either constant or depend only on tables that are outside of the outer join in question) and performns a breadth-first traversal. If we reach the outer join nest node, it means outer join is functionally dependent and can be eliminated. Otherwise it cannot be eliminated. HANDLING MULTIPLE NESTED OUTER JOINS ==================================== Outer joins that are not nested one within another are eliminated independently. For nested outer joins we have the following considerations: 1. ON expressions from children outer joins must be taken into account Consider this example: SELECT t0.* FROM t0 LEFT JOIN (t1 LEFT JOIN t2 ON t2.primary_key=t1.col1) ON t1.primary_key=t0.col AND t2.col1=t1.col2 Here we cannot eliminate the "... LEFT JOIN t2 ON ..." part alone because the ON clause of top level outer join has references to table t2. We can eliminate the entire "... LEFT JOIN (t1 LEFT JOIN t2) ON .." part, but in order to do that, we must look at both ON expressions. 2. ON expressions of parent outer joins are useless. Consider an example: SELECT t0.* FROM t0 LEFT JOIN (t1 LEFT JOIN t2 ON some_expr) ON t2.primary_key=t1.col -- (*) Here the uppermost ON expression has a clause that gives us functional dependency of table t2 on t1 and hence could be used to eliminate the "... LEFT JOIN t2 ON..." part. However, we would not actually encounter this situation, because before the table elimination we run simplify_joins(), which, among other things, upon seeing a functional dependency condition like (*) will convert the outer join of "... LEFT JOIN t2 ON ..." into inner join and thus make table elimination not to consider eliminating table t2. */ class Dep_value; class Dep_value_field; class Dep_value_table; class Dep_module; class Dep_module_expr; class Dep_module_goal; class Dep_module_key; class Dep_analysis_context; /* A value, something that can be bound or not bound. One can also iterate over unbound modules that depend on this value */ class Dep_value : public Sql_alloc { public: Dep_value(): bound(FALSE) {} virtual ~Dep_value(){} /* purecov: inspected */ /* stop compiler warnings */ bool is_bound() { return bound; } void make_bound() { bound= TRUE; } /* Iteration over unbound modules that depend on this value */ typedef char *Iterator; virtual Iterator init_unbound_modules_iter(char *buf)=0; virtual Dep_module* get_next_unbound_module(Dep_analysis_context *dac, Iterator iter) = 0; static const size_t iterator_size; protected: bool bound; }; /* A table field value. There is exactly only one such object for any tblX.fieldY - the field depends on its table and equalities - expressions that use the field are its dependencies */ class Dep_value_field : public Dep_value { public: Dep_value_field(Dep_value_table *table_arg, Field *field_arg) : table(table_arg), field(field_arg) {} Dep_value_table *table; /* Table this field is from */ Field *field; /* Field this object is representing */ /* Iteration over unbound modules that are our dependencies */ Iterator init_unbound_modules_iter(char *buf); Dep_module* get_next_unbound_module(Dep_analysis_context *dac, Iterator iter); void make_unbound_modules_iter_skip_keys(Iterator iter); static const size_t iterator_size; private: /* Field_deps that belong to one table form a linked list, ordered by field_index */ Dep_value_field *next_table_field; /* Offset to bits in Dep_analysis_context::expr_deps (see comment to that member for semantics of the bits). */ uint bitmap_offset; class Module_iter { public: /* if not null, return this and advance */ Dep_module_key *key_dep; /* Otherwise, this and advance */ uint equality_no; }; friend class Dep_analysis_context; friend class Field_dependency_recorder; friend class Dep_value_table; }; const size_t Dep_value_field::iterator_size= ALIGN_SIZE(sizeof(Dep_value_field::Module_iter)); /* A table value. There is one Dep_value_table object for every table that can potentially be eliminated. Table becomes bound as soon as some of its unique keys becomes bound Once the table is bound: - all of its fields are bound - its embedding outer join has one less unknown argument */ class Dep_value_table : public Dep_value { public: Dep_value_table(TABLE *table_arg) : table(table_arg), fields(NULL), keys(NULL) {} TABLE *table; /* Table this object is representing */ /* Ordered list of fields that belong to this table */ Dep_value_field *fields; Dep_module_key *keys; /* Ordered list of Unique keys in this table */ /* Iteration over unbound modules that are our dependencies */ Iterator init_unbound_modules_iter(char *buf); Dep_module* get_next_unbound_module(Dep_analysis_context *dac, Iterator iter); static const size_t iterator_size; private: class Module_iter { public: /* Space for field iterator */ char buf[Dep_value_field::iterator_size]; /* !NULL <=> iterating over depdenent modules of this field */ Dep_value_field *field_dep; bool returned_goal; }; }; const size_t Dep_value_table::iterator_size= ALIGN_SIZE(sizeof(Dep_value_table::Module_iter)); const size_t Dep_value::iterator_size= MY_MAX(Dep_value_table::iterator_size, Dep_value_field::iterator_size); /* A 'module'. Module has unsatisfied dependencies, number of whose is stored in unbound_args. Modules also can be linked together in a list. */ class Dep_module : public Sql_alloc { public: virtual ~Dep_module(){} /* purecov: inspected */ /* stop compiler warnings */ /* Mark as bound. Currently is non-virtual and does nothing */ void make_bound() {}; /* The final module will return TRUE here. When we see that TRUE was returned, that will mean that functional dependency check succeeded. */ virtual bool is_final () { return FALSE; } /* Increment number of bound arguments. this is expected to change is_applicable() from false to true after sufficient set of arguments is bound. */ void touch() { unbound_args--; } bool is_applicable() { return !MY_TEST(unbound_args); } /* Iteration over values that */ typedef char *Iterator; virtual Iterator init_unbound_values_iter(char *buf)=0; virtual Dep_value* get_next_unbound_value(Dep_analysis_context *dac, Iterator iter)=0; static const size_t iterator_size; protected: uint unbound_args; Dep_module() : unbound_args(0) {} /* to bump unbound_args when constructing depedendencies */ friend class Field_dependency_recorder; friend class Dep_analysis_context; }; /* This represents either - "tbl.column= expr" equality dependency, i.e. tbl.column depends on fields used in the expression, or - tbl1.col1=tbl2.col2=... multi-equality. */ class Dep_module_expr : public Dep_module { public: Dep_value_field *field; Item *expr; List *mult_equal_fields; /* Used during condition analysis only, similar to KEYUSE::level */ uint level; Iterator init_unbound_values_iter(char *buf); Dep_value* get_next_unbound_value(Dep_analysis_context *dac, Iterator iter); static const size_t iterator_size; private: class Value_iter { public: Dep_value_field *field; List_iterator it; }; }; const size_t Dep_module_expr::iterator_size= ALIGN_SIZE(sizeof(Dep_module_expr::Value_iter)); /* A Unique key module - Unique key has all of its components as arguments - Once unique key is bound, its table value is known */ class Dep_module_key: public Dep_module { public: Dep_module_key(Dep_value_table *table_arg, uint keyno_arg, uint n_parts_arg) : table(table_arg), keyno(keyno_arg), next_table_key(NULL) { unbound_args= n_parts_arg; } Dep_value_table *table; /* Table this key is from */ uint keyno; /* The index we're representing */ /* Unique keys form a linked list, ordered by keyno */ Dep_module_key *next_table_key; Iterator init_unbound_values_iter(char *buf); Dep_value* get_next_unbound_value(Dep_analysis_context *dac, Iterator iter); static const size_t iterator_size; private: class Value_iter { public: Dep_value_table *table; }; }; const size_t Dep_module_key::iterator_size= ALIGN_SIZE(sizeof(Dep_module_key::Value_iter)); const size_t Dep_module::iterator_size= MY_MAX(Dep_module_expr::iterator_size, Dep_module_key::iterator_size); /* A module that represents outer join that we're trying to eliminate. If we manage to declare this module to be bound, then outer join can be eliminated. */ class Dep_module_goal: public Dep_module { public: Dep_module_goal(uint n_children) { unbound_args= n_children; } bool is_final() { return TRUE; } /* This is the goal module, so the running wave algorithm should terminate once it sees that this module is applicable and should never try to apply it, hence no use for unbound value iterator implementation. */ Iterator init_unbound_values_iter(char *buf) { DBUG_ASSERT(0); return NULL; } Dep_value* get_next_unbound_value(Dep_analysis_context *dac, Iterator iter) { DBUG_ASSERT(0); return NULL; } }; /* Functional dependency analyzer context */ class Dep_analysis_context { public: bool setup_equality_modules_deps(List *bound_modules); bool run_wave(List *new_bound_modules); /* Tables that we're looking at eliminating */ table_map usable_tables; /* Array of equality dependencies */ Dep_module_expr *equality_mods; uint n_equality_mods; /* Number of elements in the array */ uint n_equality_mods_alloced; /* tablenr -> Dep_value_table* mapping. */ Dep_value_table *table_deps[MAX_KEY]; /* Element for the outer join we're attempting to eliminate */ Dep_module_goal *outer_join_dep; /* Bitmap of how expressions depend on bits. Given a Dep_value_field object, one can check bitmap_is_set(expr_deps, field_val->bitmap_offset + expr_no) to see if expression equality_mods[expr_no] depends on the given field. */ MY_BITMAP expr_deps; Dep_value_table *create_table_value(TABLE *table); Dep_value_field *get_field_value(Field *field); #ifndef DBUG_OFF void dbug_print_deps(); #endif }; void eliminate_tables(JOIN *join); static bool eliminate_tables_for_list(JOIN *join, List *join_list, table_map tables_in_list, Item *on_expr, table_map tables_used_elsewhere); static bool check_func_dependency(JOIN *join, table_map dep_tables, List_iterator *it, TABLE_LIST *oj_tbl, Item* cond); static void build_eq_mods_for_cond(THD *thd, Dep_analysis_context *dac, Dep_module_expr **eq_mod, uint *and_level, Item *cond); static void check_equality(Dep_analysis_context *dac, Dep_module_expr **eq_mod, uint and_level, Item_bool_func *cond, Item *left, Item *right); static Dep_module_expr *merge_eq_mods(Dep_module_expr *start, Dep_module_expr *new_fields, Dep_module_expr *end, uint and_level); static void mark_as_eliminated(JOIN *join, TABLE_LIST *tbl); static void add_module_expr(Dep_analysis_context *dac, Dep_module_expr **eq_mod, uint and_level, Dep_value_field *field_val, Item *right, List* mult_equal_fields); /*****************************************************************************/ /* Perform table elimination SYNOPSIS eliminate_tables() join Join to work on DESCRIPTION This is the entry point for table elimination. Grep for MODULE INTERFACE section in this file for calling convention. The idea behind table elimination is that if we have an outer join: SELECT * FROM t1 LEFT JOIN (t2 JOIN t3) ON t2.primary_key=t1.col AND t3.primary_key=t2.col such that 1. columns of the inner tables are not used anywhere ouside the outer join (not in WHERE, not in GROUP/ORDER BY clause, not in select list etc etc), and 2. inner side of the outer join is guaranteed to produce at most one record combination for each record combination of outer tables. then the inner side of the outer join can be removed from the query. This is because it will always produce one matching record (either a real match or a NULL-complemented record combination), and since there are no references to columns of the inner tables anywhere, it doesn't matter which record combination it was. This function primary handles checking #1. It collects a bitmap of tables that are not used in select list/GROUP BY/ORDER BY/HAVING/etc and thus can possibly be eliminated. After this, if #1 is met, the function calls eliminate_tables_for_list() that checks #2. SIDE EFFECTS See the OVERVIEW section at the top of this file. */ void eliminate_tables(JOIN *join) { THD* thd= join->thd; Item *item; table_map used_tables; DBUG_ENTER("eliminate_tables"); DBUG_ASSERT(join->eliminated_tables == 0); /* If there are no outer joins, we have nothing to eliminate: */ if (!join->outer_join) DBUG_VOID_RETURN; if (!optimizer_flag(thd, OPTIMIZER_SWITCH_TABLE_ELIMINATION)) DBUG_VOID_RETURN; /* purecov: inspected */ /* Find the tables that are referred to from WHERE/HAVING */ used_tables= (join->conds? join->conds->used_tables() : 0) | (join->having? join->having->used_tables() : 0); /* For "INSERT ... SELECT ... ON DUPLICATE KEY UPDATE column = val" we should also take into account tables mentioned in "val". */ if (join->thd->lex->sql_command == SQLCOM_INSERT_SELECT && join->select_lex == &thd->lex->select_lex) { List_iterator val_it(thd->lex->value_list); while ((item= val_it++)) { DBUG_ASSERT(item->fixed); used_tables |= item->used_tables(); } } /* Add tables referred to from the select list */ List_iterator it(join->fields_list); while ((item= it++)) used_tables |= item->used_tables(); /* Add tables referred to from ORDER BY and GROUP BY lists */ ORDER *all_lists[]= { join->order, join->group_list}; for (int i=0; i < 2; i++) { for (ORDER *cur_list= all_lists[i]; cur_list; cur_list= cur_list->next) used_tables |= (*(cur_list->item))->used_tables(); } if (join->select_lex == &thd->lex->select_lex) { /* Multi-table UPDATE: don't eliminate tables referred from SET statement */ if (thd->lex->sql_command == SQLCOM_UPDATE_MULTI) { /* Multi-table UPDATE and DELETE: don't eliminate the tables we modify: */ used_tables |= thd->table_map_for_update; List_iterator it2(thd->lex->value_list); while ((item= it2++)) used_tables |= item->used_tables(); } if (thd->lex->sql_command == SQLCOM_DELETE_MULTI) { TABLE_LIST *tbl; for (tbl= (TABLE_LIST*)thd->lex->auxiliary_table_list.first; tbl; tbl= tbl->next_local) { used_tables |= tbl->table->map; } } } table_map all_tables= join->all_tables_map(); if (all_tables & ~used_tables) { /* There are some tables that we probably could eliminate. Try it. */ eliminate_tables_for_list(join, join->join_list, all_tables, NULL, used_tables); } DBUG_VOID_RETURN; } /* Perform table elimination in a given join list SYNOPSIS eliminate_tables_for_list() join The join we're working on join_list Join list to eliminate tables from (and if on_expr !=NULL, then try eliminating join_list itself) list_tables Bitmap of tables embedded in the join_list. on_expr ON expression, if the join list is the inner side of an outer join. NULL means it's not an outer join but rather a top-level join list. tables_used_elsewhere Bitmap of tables that are referred to from somewhere outside of the join list (e.g. select list, HAVING, other ON expressions, etc). DESCRIPTION Perform table elimination in a given join list: - First, walk through join list members and try doing table elimination for them. - Then, if the join list itself is an inner side of outer join (on_expr!=NULL), then try to eliminate the entire join list. See "HANDLING MULTIPLE NESTED OUTER JOINS" section at the top of this file for more detailed description and justification. RETURN TRUE The entire join list eliminated FALSE Join list wasn't eliminated (but some of its child outer joins possibly were) */ static bool eliminate_tables_for_list(JOIN *join, List *join_list, table_map list_tables, Item *on_expr, table_map tables_used_elsewhere) { TABLE_LIST *tbl; List_iterator it(*join_list); table_map tables_used_on_left= 0; bool all_eliminated= TRUE; while ((tbl= it++)) { if (tbl->on_expr) { table_map outside_used_tables= tables_used_elsewhere | tables_used_on_left; if (on_expr) outside_used_tables |= on_expr->used_tables(); if (tbl->nested_join) { /* This is "... LEFT JOIN (join_nest) ON cond" */ if (eliminate_tables_for_list(join, &tbl->nested_join->join_list, tbl->nested_join->used_tables, tbl->on_expr, outside_used_tables)) { mark_as_eliminated(join, tbl); } else all_eliminated= FALSE; } else { /* This is "... LEFT JOIN tbl ON cond" */ if (!(tbl->table->map & outside_used_tables) && check_func_dependency(join, tbl->table->map, NULL, tbl, tbl->on_expr)) { mark_as_eliminated(join, tbl); } else all_eliminated= FALSE; } tables_used_on_left |= tbl->on_expr->used_tables(); } else { DBUG_ASSERT(!tbl->nested_join || tbl->sj_on_expr); //psergey-todo: is the following really correct or we'll need to descend //down all ON clauses: ? if (tbl->sj_on_expr) tables_used_on_left |= tbl->sj_on_expr->used_tables(); } } /* Try eliminating the nest we're called for */ if (all_eliminated && on_expr && !(list_tables & tables_used_elsewhere)) { it.rewind(); return check_func_dependency(join, list_tables & ~join->eliminated_tables, &it, NULL, on_expr); } return FALSE; /* not eliminated */ } /* Check if given condition makes given set of tables functionally dependent SYNOPSIS check_func_dependency() join Join we're procesing dep_tables Tables that we check to be functionally dependent (on everything else) it Iterator that enumerates these tables, or NULL if we're checking one single table and it is specified in oj_tbl parameter. oj_tbl NULL, or one single table that we're checking cond Condition to use to prove functional dependency DESCRIPTION Check if we can use given condition to infer that the set of given tables is functionally dependent on everything else. RETURN TRUE - Yes, functionally dependent FALSE - No, or error */ static bool check_func_dependency(JOIN *join, table_map dep_tables, List_iterator *it, TABLE_LIST *oj_tbl, Item* cond) { Dep_analysis_context dac; /* Pre-alloc some Dep_module_expr structures. We don't need this to be guaranteed upper bound. */ dac.n_equality_mods_alloced= join->thd->lex->current_select->max_equal_elems + (join->thd->lex->current_select->cond_count+1)*2 + join->thd->lex->current_select->between_count; bzero(dac.table_deps, sizeof(dac.table_deps)); if (!(dac.equality_mods= new Dep_module_expr[dac.n_equality_mods_alloced])) return FALSE; /* purecov: inspected */ Dep_module_expr* last_eq_mod= dac.equality_mods; /* Create Dep_value_table objects for all tables we're trying to eliminate */ if (oj_tbl) { if (!dac.create_table_value(oj_tbl->table)) return FALSE; /* purecov: inspected */ } else { TABLE_LIST *tbl; while ((tbl= (*it)++)) { if (tbl->table && (tbl->table->map & dep_tables)) { if (!dac.create_table_value(tbl->table)) return FALSE; /* purecov: inspected */ } } } dac.usable_tables= dep_tables; /* Analyze the the ON expression and create Dep_module_expr objects and Dep_value_field objects for the used fields. */ uint and_level=0; build_eq_mods_for_cond(join->thd, &dac, &last_eq_mod, &and_level, cond); if (!(dac.n_equality_mods= (uint)(last_eq_mod - dac.equality_mods))) return FALSE; /* No useful conditions */ List bound_modules; if (!(dac.outer_join_dep= new Dep_module_goal(my_count_bits(dep_tables))) || dac.setup_equality_modules_deps(&bound_modules)) { return FALSE; /* OOM, default to non-dependent */ /* purecov: inspected */ } DBUG_EXECUTE("test", dac.dbug_print_deps(); ); return dac.run_wave(&bound_modules); } /* Running wave functional dependency check algorithm SYNOPSIS Dep_analysis_context::run_wave() new_bound_modules List of bound modules to start the running wave from. The list is destroyed during execution DESCRIPTION This function uses running wave algorithm to check if the join nest is functionally-dependent. We start from provided list of bound modules, and then run the wave across dependency edges, trying the reach the Dep_module_goal module. If we manage to reach it, then the join nest is functionally-dependent, otherwise it is not. RETURN TRUE Yes, functionally dependent FALSE No. */ bool Dep_analysis_context::run_wave(List *new_bound_modules) { List new_bound_values; Dep_value *value; Dep_module *module; while (!new_bound_modules->is_empty()) { /* The "wave" is in new_bound_modules list. Iterate over values that can be reached from these modules but are not yet bound, and collect the next wave generation in new_bound_values list. */ List_iterator modules_it(*new_bound_modules); while ((module= modules_it++)) { char iter_buf[Dep_module::iterator_size + ALIGN_MAX_UNIT]; Dep_module::Iterator iter; iter= module->init_unbound_values_iter(iter_buf); while ((value= module->get_next_unbound_value(this, iter))) { if (!value->is_bound()) { value->make_bound(); new_bound_values.push_back(value); } } } new_bound_modules->empty(); /* Now walk over list of values we've just found to be bound and check which unbound modules can be reached from them. If there are some modules that became bound, collect them in new_bound_modules list. */ List_iterator value_it(new_bound_values); while ((value= value_it++)) { char iter_buf[Dep_value::iterator_size + ALIGN_MAX_UNIT]; Dep_value::Iterator iter; iter= value->init_unbound_modules_iter(iter_buf); while ((module= value->get_next_unbound_module(this, iter))) { module->touch(); if (!module->is_applicable()) continue; if (module->is_final()) return TRUE; /* Functionally dependent */ module->make_bound(); new_bound_modules->push_back(module); } } new_bound_values.empty(); } return FALSE; } /* This is used to analyze expressions in "tbl.col=expr" dependencies so that we can figure out which fields the expression depends on. */ class Field_dependency_recorder : public Field_enumerator { public: Field_dependency_recorder(Dep_analysis_context *ctx_arg): ctx(ctx_arg) {} void visit_field(Item_field *item) { Field *field= item->field; Dep_value_table *tbl_dep; if ((tbl_dep= ctx->table_deps[field->table->tablenr])) { for (Dep_value_field *field_dep= tbl_dep->fields; field_dep; field_dep= field_dep->next_table_field) { if (field->field_index == field_dep->field->field_index) { uint offs= field_dep->bitmap_offset + expr_offset; if (!bitmap_is_set(&ctx->expr_deps, offs)) ctx->equality_mods[expr_offset].unbound_args++; bitmap_set_bit(&ctx->expr_deps, offs); return; } } /* We got here if didn't find this field. It's not a part of a unique key, and/or there is no field=expr element for it. Bump the dependency anyway, this will signal that this dependency cannot be satisfied. */ ctx->equality_mods[expr_offset].unbound_args++; } else visited_other_tables= TRUE; } Dep_analysis_context *ctx; /* Offset of the expression we're processing in the dependency bitmap */ uint expr_offset; bool visited_other_tables; }; /* Setup inbound dependency relationships for tbl.col=expr equalities SYNOPSIS setup_equality_modules_deps() bound_deps_list Put here modules that were found not to depend on any non-bound columns. DESCRIPTION Setup inbound dependency relationships for tbl.col=expr equalities: - allocate a bitmap where we store such dependencies - for each "tbl.col=expr" equality, analyze the expr part and find out which fields it refers to and set appropriate dependencies. RETURN FALSE OK TRUE Out of memory */ bool Dep_analysis_context::setup_equality_modules_deps(List *bound_modules) { THD *thd= current_thd; DBUG_ENTER("setup_equality_modules_deps"); /* Count Dep_value_field objects and assign each of them a unique bitmap_offset value. */ uint offset= 0; for (Dep_value_table **tbl_dep= table_deps; tbl_dep < table_deps + MAX_TABLES; tbl_dep++) { if (*tbl_dep) { for (Dep_value_field *field_dep= (*tbl_dep)->fields; field_dep; field_dep= field_dep->next_table_field) { field_dep->bitmap_offset= offset; offset += n_equality_mods; } } } void *buf; if (!(buf= thd->alloc(bitmap_buffer_size(offset))) || my_bitmap_init(&expr_deps, (my_bitmap_map*)buf, offset, FALSE)) { DBUG_RETURN(TRUE); /* purecov: inspected */ } bitmap_clear_all(&expr_deps); /* Analyze all "field=expr" dependencies, and have expr_deps encode dependencies of expressions from fields. Also collect a linked list of equalities that are bound. */ Field_dependency_recorder deps_recorder(this); for (Dep_module_expr *eq_mod= equality_mods; eq_mod < equality_mods + n_equality_mods; eq_mod++) { deps_recorder.expr_offset= (uint)(eq_mod - equality_mods); deps_recorder.visited_other_tables= FALSE; eq_mod->unbound_args= 0; if (eq_mod->field) { /* Regular tbl.col=expr(tblX1.col1, tblY1.col2, ...) */ eq_mod->expr->walk(&Item::enumerate_field_refs_processor, FALSE, &deps_recorder); } else { /* It's a multi-equality */ eq_mod->unbound_args= !MY_TEST(eq_mod->expr); List_iterator it(*eq_mod->mult_equal_fields); Dep_value_field* field_val; while ((field_val= it++)) { uint offs= (uint)(field_val->bitmap_offset + eq_mod - equality_mods); bitmap_set_bit(&expr_deps, offs); } } if (!eq_mod->unbound_args) bound_modules->push_back(eq_mod, thd->mem_root); } DBUG_RETURN(FALSE); } /* Ordering that we're using whenever we need to maintain a no-duplicates list of field value objects. */ static int compare_field_values(Dep_value_field *a, Dep_value_field *b, void *unused) { uint a_ratio= a->field->table->tablenr*MAX_FIELDS + a->field->field_index; uint b_ratio= b->field->table->tablenr*MAX_FIELDS + b->field->field_index; return (a_ratio < b_ratio)? 1 : ((a_ratio == b_ratio)? 0 : -1); } /* Produce Dep_module_expr elements for given condition. SYNOPSIS build_eq_mods_for_cond() ctx Table elimination context eq_mod INOUT Put produced equality conditions here and_level INOUT AND-level (like in add_key_fields) cond Condition to process DESCRIPTION Analyze the given condition and produce an array of Dep_module_expr dependencies from it. The idea of analysis is as follows: There are useful equalities that have form eliminable_tbl.field = expr (denote as useful_equality) The condition is composed of useful equalities and other conditions that are combined together with AND and OR operators. We process the condition in recursive fashion according to these basic rules: useful_equality1 AND useful_equality2 -> make array of two Dep_module_expr objects useful_equality AND other_cond -> discard other_cond useful_equality OR other_cond -> discard everything useful_equality1 OR useful_equality2 -> check if both sides of OR are the same equality. If yes, that's the result, otherwise discard everything. The rules are used to map the condition into an array Dep_module_expr elements. The array will specify functional dependencies that logically follow from the condition. SEE ALSO This function is modeled after add_key_fields() */ static void build_eq_mods_for_cond(THD *thd, Dep_analysis_context *ctx, Dep_module_expr **eq_mod, uint *and_level, Item *cond) { if (cond->type() == Item_func::COND_ITEM) { List_iterator_fast li(*((Item_cond*) cond)->argument_list()); size_t orig_offset= *eq_mod - ctx->equality_mods; /* AND/OR */ if (((Item_cond*) cond)->functype() == Item_func::COND_AND_FUNC) { Item *item; while ((item=li++)) build_eq_mods_for_cond(thd, ctx, eq_mod, and_level, item); for (Dep_module_expr *mod_exp= ctx->equality_mods + orig_offset; mod_exp != *eq_mod ; mod_exp++) { mod_exp->level= *and_level; } } else { Item *item; (*and_level)++; build_eq_mods_for_cond(thd, ctx, eq_mod, and_level, li++); while ((item=li++)) { Dep_module_expr *start_key_fields= *eq_mod; (*and_level)++; build_eq_mods_for_cond(thd, ctx, eq_mod, and_level, item); *eq_mod= merge_eq_mods(ctx->equality_mods + orig_offset, start_key_fields, *eq_mod, ++(*and_level)); } } return; } if (cond->type() != Item::FUNC_ITEM) return; Item_func *cond_func= (Item_func*) cond; Item **args= cond_func->arguments(); switch (cond_func->functype()) { case Item_func::BETWEEN: { Item *fld; Item_func_between *func= (Item_func_between *) cond_func; if (!func->negated && (fld= args[0]->real_item())->type() == Item::FIELD_ITEM && args[1]->eq(args[2], ((Item_field*)fld)->field->binary())) { check_equality(ctx, eq_mod, *and_level, func, args[0], args[1]); check_equality(ctx, eq_mod, *and_level, func, args[1], args[0]); } break; } case Item_func::EQ_FUNC: case Item_func::EQUAL_FUNC: { Item_bool_rowready_func2 *func= (Item_bool_rowready_func2*) cond_func; check_equality(ctx, eq_mod, *and_level, func, args[0], args[1]); check_equality(ctx, eq_mod, *and_level, func, args[1], args[0]); break; } case Item_func::ISNULL_FUNC: { Item *tmp=new (thd->mem_root) Item_null(thd); if (tmp) check_equality(ctx, eq_mod, *and_level, (Item_func_isnull*) cond_func, args[0], tmp); break; } case Item_func::MULT_EQUAL_FUNC: { /* The condition is a tbl1.field1 = tbl2.field2 = tbl3.field3 [= const_expr] multiple-equality. Do two things: - Collect List of tblX.colY where tblX is one of the tables we're trying to eliminate. - rembember if there was a bound value, either const_expr or tblY.colZ swher tblY is not a table that we're trying to eliminate. Store all collected information in a Dep_module_expr object. */ Item_equal *item_equal= (Item_equal*)cond; List *fvl; if (!(fvl= new List)) break; /* purecov: inspected */ Item_equal_fields_iterator it(*item_equal); Item *item; Item *bound_item= item_equal->get_const(); while ((item= it++)) { Field *equal_field= it.get_curr_field(); if ((item->used_tables() & ctx->usable_tables)) { Dep_value_field *field_val; if ((field_val= ctx->get_field_value(equal_field))) fvl->push_back(field_val, thd->mem_root); } else { if (!bound_item) bound_item= item; } } /* Multiple equality is only useful if it includes at least one field from the table that we could potentially eliminate: */ if (fvl->elements) { bubble_sort(fvl, compare_field_values, NULL); add_module_expr(ctx, eq_mod, *and_level, NULL, bound_item, fvl); } break; } default: break; } } /* Perform an OR operation on two (adjacent) Dep_module_expr arrays. SYNOPSIS merge_eq_mods() start Start of left OR-part new_fields Start of right OR-part end End of right OR-part and_level AND-level (like in add_key_fields) DESCRIPTION This function is invoked for two adjacent arrays of Dep_module_expr elements: $LEFT_PART $RIGHT_PART +-----------------------+-----------------------+ start new_fields end The goal is to produce an array which would correspond to the combined $LEFT_PART OR $RIGHT_PART condition. This is achieved as follows: First, we apply distrubutive law: (fdep_A_1 AND fdep_A_2 AND ...) OR (fdep_B_1 AND fdep_B_2 AND ...) = = AND_ij (fdep_A_[i] OR fdep_B_[j]) Then we walk over the obtained "fdep_A_[i] OR fdep_B_[j]" pairs, and - Discard those that that have left and right part referring to different columns. We can't infer anything useful from "col1=expr1 OR col2=expr2". - When left and right parts refer to the same column, we check if they are essentially the same. = If they are the same, we keep one copy "t.col=expr OR t.col=expr" -> "t.col=expr = if they are different , then we discard both "t.col=expr1 OR t.col=expr2" -> (nothing useful) (no per-table or for-index FUNC_DEPS exist yet at this phase). See also merge_key_fields(). RETURN End of the result array */ static Dep_module_expr *merge_eq_mods(Dep_module_expr *start, Dep_module_expr *new_fields, Dep_module_expr *end, uint and_level) { if (start == new_fields) return start; /* (nothing) OR (...) -> (nothing) */ if (new_fields == end) return start; /* (...) OR (nothing) -> (nothing) */ Dep_module_expr *first_free= new_fields; for (; new_fields != end ; new_fields++) { for (Dep_module_expr *old=start ; old != first_free ; old++) { if (old->field == new_fields->field) { if (!old->field) { /* OR-ing two multiple equalities. We must compute an intersection of used fields, and check the constants according to these rules: a=b=c=d OR a=c=e=f -> a=c (compute intersection) a=const1 OR a=b -> (nothing) a=const1 OR a=const1 -> a=const1 a=const1 OR a=const2 -> (nothing) If we're performing an OR operation over multiple equalities, e.g. (a=b=c AND p=q) OR (a=b AND v=z) then we'll need to try combining each equality with each. ANDed equalities are guaranteed to be disjoint, so we'll only get one hit. */ Field *eq_field= old->mult_equal_fields->head()->field; if (old->expr && new_fields->expr && old->expr->eq_by_collation(new_fields->expr, eq_field->binary(), eq_field->charset())) { /* Ok, keep */ } else { /* no single constant/bound item. */ old->expr= NULL; } List *fv; if (!(fv= new List)) break; /* purecov: inspected */ List_iterator it1(*old->mult_equal_fields); List_iterator it2(*new_fields->mult_equal_fields); Dep_value_field *lfield= it1++; Dep_value_field *rfield= it2++; /* Intersect two ordered lists */ while (lfield && rfield) { if (lfield == rfield) { fv->push_back(lfield); lfield=it1++; rfield=it2++; } else { if (compare_field_values(lfield, rfield, NULL) < 0) lfield= it1++; else rfield= it2++; } } if (fv->elements + MY_TEST(old->expr) > 1) { old->mult_equal_fields= fv; old->level= and_level; } } else if (!new_fields->expr->const_item()) { /* If the value matches, we can use the key reference. If not, we keep it until we have examined all new values */ if (old->expr->eq(new_fields->expr, old->field->field->binary())) { old->level= and_level; } } else if (old->expr->eq_by_collation(new_fields->expr, old->field->field->binary(), old->field->field->charset())) { old->level= and_level; } else { /* The expressions are different. */ if (old == --first_free) // If last item break; *old= *first_free; // Remove old value old--; // Retry this value } } } } /* Ok, the results are within the [start, first_free) range, and the useful elements have level==and_level. Now, remove all unusable elements: */ for (Dep_module_expr *old=start ; old != first_free ;) { if (old->level != and_level) { // Not used in all levels if (old == --first_free) break; *old= *first_free; // Remove old value continue; } old++; } return first_free; } /* Add an Dep_module_expr element for left=right condition SYNOPSIS check_equality() fda Table elimination context eq_mod INOUT Store created Dep_module_expr here and increment ptr if you do so and_level AND-level (like in add_key_fields) cond Condition we've inferred the left=right equality from. left Left expression right Right expression usable_tables Create Dep_module_expr only if Left_expression's table belongs to this set. DESCRIPTION Check if the passed left=right equality is such that - 'left' is an Item_field referring to a field in a table we're checking to be functionally depdendent, - the equality allows to conclude that 'left' expression is functionally dependent on the 'right', and if so, create an Dep_module_expr object. */ static void check_equality(Dep_analysis_context *ctx, Dep_module_expr **eq_mod, uint and_level, Item_bool_func *cond, Item *left, Item *right) { if ((left->used_tables() & ctx->usable_tables) && !(right->used_tables() & RAND_TABLE_BIT) && left->real_item()->type() == Item::FIELD_ITEM) { Field *field= ((Item_field*)left->real_item())->field; if (!field->can_optimize_outer_join_table_elimination(cond, right)) return; Dep_value_field *field_val; if ((field_val= ctx->get_field_value(field))) add_module_expr(ctx, eq_mod, and_level, field_val, right, NULL); } } /* Add a Dep_module_expr object with the specified parameters. DESCRIPTION Add a Dep_module_expr object with the specified parameters. Re-allocate the ctx->equality_mods array if it has no space left. */ static void add_module_expr(Dep_analysis_context *ctx, Dep_module_expr **eq_mod, uint and_level, Dep_value_field *field_val, Item *right, List* mult_equal_fields) { if (*eq_mod == ctx->equality_mods + ctx->n_equality_mods_alloced) { /* We've filled the entire equality_mods array. Replace it with a bigger one. We do it somewhat inefficiently but it doesn't matter. */ /* purecov: begin inspected */ Dep_module_expr *new_arr; if (!(new_arr= new Dep_module_expr[ctx->n_equality_mods_alloced *2])) return; ctx->n_equality_mods_alloced *= 2; for (int i= 0; i < *eq_mod - ctx->equality_mods; i++) new_arr[i]= ctx->equality_mods[i]; ctx->equality_mods= new_arr; *eq_mod= new_arr + (*eq_mod - ctx->equality_mods); /* purecov: end */ } (*eq_mod)->field= field_val; (*eq_mod)->expr= right; (*eq_mod)->level= and_level; (*eq_mod)->mult_equal_fields= mult_equal_fields; (*eq_mod)++; } /* Create a Dep_value_table object for the given table SYNOPSIS Dep_analysis_context::create_table_value() table Table to create object for DESCRIPTION Create a Dep_value_table object for the given table. Also create Dep_module_key objects for all unique keys in the table. RETURN Created table value object NULL if out of memory */ Dep_value_table *Dep_analysis_context::create_table_value(TABLE *table) { Dep_value_table *tbl_dep; if (!(tbl_dep= new Dep_value_table(table))) return NULL; /* purecov: inspected */ Dep_module_key **key_list= &(tbl_dep->keys); /* Add dependencies for unique keys */ for (uint i=0; i < table->s->keys; i++) { KEY *key= table->key_info + i; if (key->flags & HA_NOSAME) { Dep_module_key *key_dep; if (!(key_dep= new Dep_module_key(tbl_dep, i, key->user_defined_key_parts))) return NULL; *key_list= key_dep; key_list= &(key_dep->next_table_key); } } return table_deps[table->tablenr]= tbl_dep; } /* Get a Dep_value_field object for the given field, creating it if necessary SYNOPSIS Dep_analysis_context::get_field_value() field Field to create object for DESCRIPTION Get a Dep_value_field object for the given field. First, we search for it in the list of Dep_value_field objects we have already created. If we don't find it, we create a new Dep_value_field and put it into the list of field objects we have for the table. RETURN Created field value object NULL if out of memory */ Dep_value_field *Dep_analysis_context::get_field_value(Field *field) { TABLE *table= field->table; Dep_value_table *tbl_dep= table_deps[table->tablenr]; /* Try finding the field in field list */ Dep_value_field **pfield= &(tbl_dep->fields); while (*pfield && (*pfield)->field->field_index < field->field_index) { pfield= &((*pfield)->next_table_field); } if (*pfield && (*pfield)->field->field_index == field->field_index) return *pfield; /* Create the field and insert it in the list */ Dep_value_field *new_field= new Dep_value_field(tbl_dep, field); new_field->next_table_field= *pfield; *pfield= new_field; return new_field; } /* Iteration over unbound modules that are our dependencies. for those we have: - dependendencies of our fields - outer join we're in */ char *Dep_value_table::init_unbound_modules_iter(char *buf) { Module_iter *iter= ALIGN_PTR(my_ptrdiff_t(buf), Module_iter); iter->field_dep= fields; if (fields) { fields->init_unbound_modules_iter(iter->buf); fields->make_unbound_modules_iter_skip_keys(iter->buf); } iter->returned_goal= FALSE; return (char*)iter; } Dep_module* Dep_value_table::get_next_unbound_module(Dep_analysis_context *dac, char *iter) { Module_iter *di= (Module_iter*)iter; while (di->field_dep) { Dep_module *res; if ((res= di->field_dep->get_next_unbound_module(dac, di->buf))) return res; if ((di->field_dep= di->field_dep->next_table_field)) { char *field_iter= ((Module_iter*)iter)->buf; di->field_dep->init_unbound_modules_iter(field_iter); di->field_dep->make_unbound_modules_iter_skip_keys(field_iter); } } if (!di->returned_goal) { di->returned_goal= TRUE; return dac->outer_join_dep; } return NULL; } char *Dep_module_expr::init_unbound_values_iter(char *buf) { Value_iter *iter= ALIGN_PTR(my_ptrdiff_t(buf), Value_iter); iter->field= field; if (!field) { new (&iter->it) List_iterator(*mult_equal_fields); } return (char*)iter; } Dep_value* Dep_module_expr::get_next_unbound_value(Dep_analysis_context *dac, char *buf) { Dep_value *res; if (field) { res= ((Value_iter*)buf)->field; ((Value_iter*)buf)->field= NULL; return (!res || res->is_bound())? NULL : res; } else { while ((res= ((Value_iter*)buf)->it++)) { if (!res->is_bound()) return res; } return NULL; } } char *Dep_module_key::init_unbound_values_iter(char *buf) { Value_iter *iter= ALIGN_PTR(my_ptrdiff_t(buf), Value_iter); iter->table= table; return (char*)iter; } Dep_value* Dep_module_key::get_next_unbound_value(Dep_analysis_context *dac, Dep_module::Iterator iter) { Dep_value* res= ((Value_iter*)iter)->table; ((Value_iter*)iter)->table= NULL; return res; } Dep_value::Iterator Dep_value_field::init_unbound_modules_iter(char *buf) { Module_iter *iter= ALIGN_PTR(my_ptrdiff_t(buf), Module_iter); iter->key_dep= table->keys; iter->equality_no= 0; return (char*)iter; } void Dep_value_field::make_unbound_modules_iter_skip_keys(Dep_value::Iterator iter) { ((Module_iter*)iter)->key_dep= NULL; } Dep_module* Dep_value_field::get_next_unbound_module(Dep_analysis_context *dac, Dep_value::Iterator iter) { Module_iter *di= (Module_iter*)iter; Dep_module_key *key_dep= di->key_dep; /* First, enumerate all unique keys that are - not yet applicable - have this field as a part of them */ while (key_dep && (key_dep->is_applicable() || !field->part_of_key_not_clustered.is_set(key_dep->keyno))) { key_dep= key_dep->next_table_key; } if (key_dep) { di->key_dep= key_dep->next_table_key; return key_dep; } else di->key_dep= NULL; /* Then walk through [multi]equalities and find those that - depend on this field - and are not bound yet. */ uint eq_no= di->equality_no; while (eq_no < dac->n_equality_mods && (!bitmap_is_set(&dac->expr_deps, bitmap_offset + eq_no) || dac->equality_mods[eq_no].is_applicable())) { eq_no++; } if (eq_no < dac->n_equality_mods) { di->equality_no= eq_no+1; return &dac->equality_mods[eq_no]; } return NULL; } /* Mark one table or the whole join nest as eliminated. */ static void mark_as_eliminated(JOIN *join, TABLE_LIST *tbl) { TABLE *table; /* NOTE: there are TABLE_LIST object that have tbl->table!= NULL && tbl->nested_join!=NULL and tbl->table == tbl->nested_join->join_list->element(..)->table */ if (tbl->nested_join) { TABLE_LIST *child; List_iterator it(tbl->nested_join->join_list); while ((child= it++)) mark_as_eliminated(join, child); } else if ((table= tbl->table)) { JOIN_TAB *tab= tbl->table->reginfo.join_tab; if (!(join->const_table_map & tab->table->map)) { DBUG_PRINT("info", ("Eliminated table %s", table->alias.c_ptr())); tab->type= JT_CONST; join->eliminated_tables |= table->map; join->const_table_map|= table->map; set_position(join, join->const_tables++, tab, (KEYUSE*)0); } } if (tbl->on_expr) tbl->on_expr->walk(&Item::mark_as_eliminated_processor, FALSE, NULL); } #ifndef DBUG_OFF /* purecov: begin inspected */ void Dep_analysis_context::dbug_print_deps() { DBUG_ENTER("dbug_print_deps"); DBUG_LOCK_FILE; fprintf(DBUG_FILE,"deps {\n"); /* Start with printing equalities */ for (Dep_module_expr *eq_mod= equality_mods; eq_mod != equality_mods + n_equality_mods; eq_mod++) { char buf[128]; String str(buf, sizeof(buf), &my_charset_bin); str.length(0); eq_mod->expr->print(&str, QT_ORDINARY); if (eq_mod->field) { fprintf(DBUG_FILE, " equality%ld: %s -> %s.%s\n", (long)(eq_mod - equality_mods), str.c_ptr(), eq_mod->field->table->table->alias.c_ptr(), eq_mod->field->field->field_name); } else { fprintf(DBUG_FILE, " equality%ld: multi-equality", (long)(eq_mod - equality_mods)); } } fprintf(DBUG_FILE,"\n"); /* Then tables and their fields */ for (uint i=0; i < MAX_TABLES; i++) { Dep_value_table *table_dep; if ((table_dep= table_deps[i])) { /* Print table */ fprintf(DBUG_FILE, " table %s\n", table_dep->table->alias.c_ptr()); /* Print fields */ for (Dep_value_field *field_dep= table_dep->fields; field_dep; field_dep= field_dep->next_table_field) { fprintf(DBUG_FILE, " field %s.%s ->", table_dep->table->alias.c_ptr(), field_dep->field->field_name); uint ofs= field_dep->bitmap_offset; for (uint bit= ofs; bit < ofs + n_equality_mods; bit++) { if (bitmap_is_set(&expr_deps, bit)) fprintf(DBUG_FILE, " equality%d ", bit - ofs); } fprintf(DBUG_FILE, "\n"); } } } fprintf(DBUG_FILE,"\n}\n"); DBUG_UNLOCK_FILE; DBUG_VOID_RETURN; } /* purecov: end */ #endif /** @} (end of group Table_Elimination) */