diff options
Diffstat (limited to 'sql/sql_expression_cache.cc')
| -rw-r--r-- | sql/sql_expression_cache.cc | 314 |
1 files changed, 314 insertions, 0 deletions
diff --git a/sql/sql_expression_cache.cc b/sql/sql_expression_cache.cc new file mode 100644 index 00000000000..70c36b141b6 --- /dev/null +++ b/sql/sql_expression_cache.cc @@ -0,0 +1,314 @@ + +#include "mysql_priv.h" +#include "sql_select.h" + +/* + Expression cache is used only for caching subqueries now, so its statistic + variables we call subquery_cache*. +*/ +ulonglong subquery_cache_miss, subquery_cache_hit; + +Expression_cache_tmptable::Expression_cache_tmptable(THD *thd, + List<Item*> &dependants, + Item *value) + :cache_table(NULL), table_thd(thd), list(&dependants), val(value), + equalities(NULL), inited (0) +{ + DBUG_ENTER("Expression_cache_tmptable::Expression_cache_tmptable"); + DBUG_VOID_RETURN; +}; + + +/** + Build and of equalities for the expression's parameters of certain types + + @details + If the temporary table used as an expression cache contains fields of + certain types then it's not enough to perform a lookup into the table to + verify that there is no row in the table for a given set of parameters. + Additionally for those fields we have to check equalities of the form + fld=val, where val is the value of the parameter stored in the column + fld. + The function generates a conjunction of all such equality predicates + and saves a pointer to it in the field 'equalities'. + + @retval FALSE OK + @retval TRUE Error +*/ + +bool Expression_cache_tmptable::make_equalities() +{ + List<Item> args; + List_iterator_fast<Item*> li(*list); + Item **ref; + Name_resolution_context *cn= NULL; + DBUG_ENTER("Expression_cache_tmptable::make_equalities"); + + for (uint i= 1 /* skip result filed */; (ref= li++); i++) + { + Field *fld= cache_table->field[i]; + /* Only some field types should be checked after lookup */ + if (fld->type() == MYSQL_TYPE_VARCHAR || + fld->type() == MYSQL_TYPE_TINY_BLOB || + fld->type() == MYSQL_TYPE_MEDIUM_BLOB || + fld->type() == MYSQL_TYPE_LONG_BLOB || + fld->type() == MYSQL_TYPE_BLOB || + fld->type() == MYSQL_TYPE_VAR_STRING || + fld->type() == MYSQL_TYPE_STRING || + fld->type() == MYSQL_TYPE_NEWDECIMAL || + fld->type() == MYSQL_TYPE_DECIMAL) + { + if (!cn) + { + // dummy resolution context + cn= new Name_resolution_context(); + cn->init(); + } + args.push_front(new Item_func_eq(new Item_ref(cn, ref, "", "", FALSE), + new Item_field(fld))); + } + } + if (args.elements == 1) + equalities= args.head(); + else + equalities= new Item_cond_and(args); + + DBUG_RETURN(equalities->fix_fields(table_thd, &equalities)); +} + + +/** + Field enumerator for TABLE::add_tmp_key + + @param arg reference variable with current field number + + @return field number +*/ + +static uint field_enumerator(uchar *arg) +{ + return ((uint*)arg)[0]++; +} + + +/** + Initialize temporary table and auxiliary structures for the expression + cache + + @details + The function creates a temporary table for the expression cache, defines + the search index and initializes auxiliary search structures used to check + whether a given set of of values of the expression parameters is in some + cache entry. +*/ + +void Expression_cache_tmptable::init() +{ + List_iterator_fast<Item*> li(*list); + Item_iterator_ref_list it(li); + Item **item; + uint field_counter; + DBUG_ENTER("Expression_cache_tmptable::init"); + DBUG_ASSERT(!inited); + inited= TRUE; + + if (!(ULONGLONG_MAX >> (list->elements + 1))) + { + DBUG_PRINT("info", ("Too many dependencies")); + DBUG_VOID_RETURN; + } + + cache_table= NULL; + + cache_table_param.init(); + /* dependent items and result */ + cache_table_param.field_count= list->elements + 1; + /* postpone table creation to index description */ + cache_table_param.skip_create_table= 1; + cache_table= NULL; + + while ((item= li++)) + { + DBUG_ASSERT(item); + DBUG_ASSERT(*item); + DBUG_ASSERT((*item)->fixed); + items.push_back((*item)); + } + items.push_front(val); + + if (!(cache_table= create_tmp_table(table_thd, &cache_table_param, + items, (ORDER*) NULL, + FALSE, FALSE, + ((table_thd->options | + TMP_TABLE_ALL_COLUMNS) & + ~(OPTION_BIG_TABLES | + TMP_TABLE_FORCE_MYISAM)), + HA_POS_ERROR, + (char *)"subquery-cache-table"))) + { + DBUG_PRINT("error", ("create_tmp_table failed, caching switched off")); + DBUG_VOID_RETURN; + } + + if (cache_table->s->db_type() != heap_hton) + { + DBUG_PRINT("error", ("we need only heap table")); + goto error; + } + + /* This list do not contain result field */ + it.open(); + + field_counter=1; + + if (cache_table->alloc_keys(1) || + (cache_table->add_tmp_key(0, items.elements - 1, + &field_enumerator, + (uchar*)&field_counter) < 0) || + ref.tmp_table_index_lookup_init(table_thd, cache_table->key_info, it, + TRUE)) + { + DBUG_PRINT("error", ("creating index failed")); + goto error; + } + cache_table->s->keys= 1; + cache_table->s->uniques= 1; + ref.null_rejecting= 1; + ref.disable_cache= FALSE; + ref.has_record= 0; + ref.use_count= 0; + + + if (open_tmp_table(cache_table)) + { + DBUG_PRINT("error", ("Opening (creating) temporary table failed")); + goto error; + } + + if (!(cached_result= new Item_field(cache_table->field[0]))) + { + DBUG_PRINT("error", ("Creating Item_field failed")); + goto error; + } + + if (make_equalities()) + { + DBUG_PRINT("error", ("Creating equalities failed")); + goto error; + } + + DBUG_VOID_RETURN; + +error: + /* switch off cache */ + free_tmp_table(table_thd, cache_table); + cache_table= NULL; + DBUG_VOID_RETURN; +} + + +Expression_cache_tmptable::~Expression_cache_tmptable() +{ + if (cache_table) + free_tmp_table(table_thd, cache_table); +} + + +/** + Check if a given set of parameters of the expression is in the cache + + @param [out] value the expression value found in the cache if any + + @details + For a given set of the parameters of the expression the function + checks whether it can be found in some entry of the cache. If so + the function returns the result of the expression extracted from + the cache. + + @retval Expression_cache::HIT if the set of parameters is in the cache + @retval Expression_cache::MISS - otherwise +*/ + +Expression_cache::result Expression_cache_tmptable::check_value(Item **value) +{ + int res; + DBUG_ENTER("Expression_cache_tmptable::check_value"); + + /* + We defer cache initialization to get item references that are + used at the execution phase. + */ + if (!inited) + init(); + + if (cache_table) + { + DBUG_PRINT("info", ("status: %u has_record %u", + (uint)cache_table->status, (uint)ref.has_record)); + if ((res= join_read_key2(table_thd, NULL, cache_table, &ref)) == 1) + DBUG_RETURN(ERROR); + if (res || (equalities && !equalities->val_int())) + { + subquery_cache_miss++; + DBUG_RETURN(MISS); + } + + subquery_cache_hit++; + *value= cached_result; + DBUG_RETURN(Expression_cache::HIT); + } + DBUG_RETURN(Expression_cache::MISS); +} + + +/** + Put a new entry into the expression cache + + @param value the result of the expression to be put into the cache + + @details + The function evaluates 'value' and puts the result into the cache as the + result of the expression for the current set of parameters. + + @retval FALSE OK + @retval TRUE Error +*/ + +my_bool Expression_cache_tmptable::put_value(Item *value) +{ + int error; + DBUG_ENTER("Expression_cache_tmptable::put_value"); + DBUG_ASSERT(inited); + + if (!cache_table) + { + DBUG_PRINT("info", ("No table so behave as we successfully put value")); + DBUG_RETURN(FALSE); + } + + *(items.head_ref())= value; + fill_record(table_thd, cache_table->field, items, TRUE, TRUE); + if (table_thd->is_error()) + goto err;; + + if ((error= cache_table->file->ha_write_row(cache_table->record[0]))) + { + /* create_myisam_from_heap will generate error if needed */ + if (cache_table->file->is_fatal_error(error, HA_CHECK_DUP) && + create_internal_tmp_table_from_heap(table_thd, cache_table, + cache_table_param.start_recinfo, + &cache_table_param.recinfo, + error, 1)) + goto err; + } + cache_table->status= 0; /* cache_table->record contains an existed record */ + ref.has_record= TRUE; /* the same as above */ + DBUG_PRINT("info", ("has_record: TRUE status: 0")); + + DBUG_RETURN(FALSE); + +err: + free_tmp_table(table_thd, cache_table); + cache_table= NULL; + DBUG_RETURN(TRUE); +} |