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Diffstat (limited to 'sql/opt_index_cond_pushdown.cc')
| -rw-r--r-- | sql/opt_index_cond_pushdown.cc | 442 |
1 files changed, 442 insertions, 0 deletions
diff --git a/sql/opt_index_cond_pushdown.cc b/sql/opt_index_cond_pushdown.cc new file mode 100644 index 00000000..6a24fa95 --- /dev/null +++ b/sql/opt_index_cond_pushdown.cc @@ -0,0 +1,442 @@ +/* + Copyright (c) 2009, 2012, 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 02110-1335 USA */ + +#include "mariadb.h" +#include "sql_select.h" +#include "sql_test.h" + +/**************************************************************************** + * Index Condition Pushdown code starts + ***************************************************************************/ +/* + Check if given expression uses only table fields covered by the given index + + SYNOPSIS + uses_index_fields_only() + item Expression to check + tbl The table having the index + keyno The index number + other_tbls_ok TRUE <=> Fields of other non-const tables are allowed + + DESCRIPTION + Check if given expression only uses fields covered by index #keyno in the + table tbl. The expression can use any fields in any other tables. + + The expression is guaranteed not to be AND or OR - those constructs are + handled outside of this function. + + RETURN + TRUE Yes + FALSE No +*/ + +bool uses_index_fields_only(Item *item, TABLE *tbl, uint keyno, + bool other_tbls_ok) +{ + if (item->walk(&Item::limit_index_condition_pushdown_processor, FALSE, NULL)) + { + return FALSE; + } + + if (item->const_item()) + return TRUE; + + /* + Don't push down the triggered conditions. Nested outer joins execution + code may need to evaluate a condition several times (both triggered and + untriggered), and there is no way to put thi + TODO: Consider cloning the triggered condition and using the copies for: + 1. push the first copy down, to have most restrictive index condition + possible + 2. Put the second copy into tab->select_cond. + */ + if (item->type() == Item::FUNC_ITEM && + ((Item_func*)item)->functype() == Item_func::TRIG_COND_FUNC) + return FALSE; + + if (!(item->used_tables() & tbl->map)) + return other_tbls_ok; + + Item::Type item_type= item->type(); + switch (item_type) { + case Item::FUNC_ITEM: + { + /* This is a function, apply condition recursively to arguments */ + Item_func *item_func= (Item_func*)item; + Item **child; + Item **item_end= (item_func->arguments()) + item_func->argument_count(); + for (child= item_func->arguments(); child != item_end; child++) + { + if (!uses_index_fields_only(*child, tbl, keyno, other_tbls_ok)) + return FALSE; + } + return TRUE; + } + case Item::COND_ITEM: + { + /* + This is a AND/OR condition. Regular AND/OR clauses are handled by + make_cond_for_index() which will chop off the part that can be + checked with index. This code is for handling non-top-level AND/ORs, + e.g. func(x AND y). + */ + List_iterator<Item> li(*((Item_cond*)item)->argument_list()); + Item *item; + while ((item=li++)) + { + if (!uses_index_fields_only(item, tbl, keyno, other_tbls_ok)) + return FALSE; + } + return TRUE; + } + case Item::FIELD_ITEM: + { + Item_field *item_field= (Item_field*)item; + Field *field= item_field->field; + if (field->table != tbl) + return TRUE; + /* + The below is probably a repetition - the first part checks the + other two, but let's play it safe: + */ + if(!field->part_of_key.is_set(keyno) || + field->type() == MYSQL_TYPE_GEOMETRY || + field->type() == MYSQL_TYPE_BLOB) + return FALSE; + KEY *key_info= tbl->key_info + keyno; + KEY_PART_INFO *key_part= key_info->key_part; + KEY_PART_INFO *key_part_end= key_part + key_info->user_defined_key_parts; + for ( ; key_part < key_part_end; key_part++) + { + if (field->eq(key_part->field)) + return !(key_part->key_part_flag & HA_PART_KEY_SEG); + } + if ((tbl->file->ha_table_flags() & HA_PRIMARY_KEY_IN_READ_INDEX) && + tbl->s->primary_key != MAX_KEY && + tbl->s->primary_key != keyno) + { + key_info= tbl->key_info + tbl->s->primary_key; + key_part= key_info->key_part; + key_part_end= key_part + key_info->user_defined_key_parts; + for ( ; key_part < key_part_end; key_part++) + { + /* + It does not make sense to use the fact that the engine can read in + a full field if the key if the index is built only over a part + of this field. + */ + if (field->eq(key_part->field)) + return !(key_part->key_part_flag & HA_PART_KEY_SEG); + } + } + return FALSE; + } + case Item::REF_ITEM: + return uses_index_fields_only(item->real_item(), tbl, keyno, + other_tbls_ok); + default: + return FALSE; /* Play it safe, don't push unknown non-const items */ + } +} + + +/* + Get a part of the condition that can be checked using only index fields + + SYNOPSIS + make_cond_for_index() + cond The source condition + table The table that is partially available + keyno The index in the above table. Only fields covered by the + index are available + other_tbls_ok TRUE <=> Fields of other non-const tables are allowed + + DESCRIPTION + Get a part of the condition that can be checked when for the given table + we have values only of fields covered by some index. The condition may + refer to other tables, it is assumed that we have values of all of their + fields. + + Example: + make_cond_for_index( + "cond(t1.field) AND cond(t2.key1) AND cond(t2.non_key) AND cond(t2.key2)", + t2, keyno(t2.key1)) + will return + "cond(t1.field) AND cond(t2.key2)" + + RETURN + Index condition, or NULL if no condition could be inferred. +*/ + +static Item *make_cond_for_index(THD *thd, Item *cond, TABLE *table, uint keyno, + bool other_tbls_ok) +{ + if (!cond || cond->basic_const_item()) + return cond; + if (cond->type() == Item::COND_ITEM) + { + if (((Item_cond*) cond)->functype() == Item_func::COND_AND_FUNC) + { + table_map used_tables= 0; + Item_cond_and *new_cond= new (thd->mem_root) Item_cond_and(thd); + if (!new_cond) + return (COND*) 0; + List_iterator<Item> li(*((Item_cond*) cond)->argument_list()); + Item *item; + while ((item=li++)) + { + Item *fix= make_cond_for_index(thd, item, table, keyno, other_tbls_ok); + if (fix) + { + new_cond->argument_list()->push_back(fix, thd->mem_root); + used_tables|= fix->used_tables(); + } + } + switch (new_cond->argument_list()->elements) { + case 0: + return (COND*) 0; + case 1: + /* remove AND level if there is only one argument */ + return new_cond->argument_list()->head(); + default: + new_cond->quick_fix_field(); + new_cond->used_tables_cache= used_tables; + return new_cond; + } + } + else /* It's OR */ + { + Item_cond_or *new_cond= new (thd->mem_root) Item_cond_or(thd); + if (!new_cond) + return (COND*) 0; + List_iterator<Item> li(*((Item_cond*) cond)->argument_list()); + Item *item; + while ((item=li++)) + { + Item *fix= make_cond_for_index(thd, item, table, keyno, other_tbls_ok); + if (!fix) + return (COND*) 0; + new_cond->argument_list()->push_back(fix, thd->mem_root); + } + new_cond->quick_fix_field(); + new_cond->used_tables_cache= ((Item_cond_or*) cond)->used_tables_cache; + new_cond->top_level_item(); + return new_cond; + } + } + + if (!uses_index_fields_only(cond, table, keyno, other_tbls_ok)) + return (COND*) 0; + return cond; +} + + +static Item *make_cond_remainder(THD *thd, Item *cond, TABLE *table, uint keyno, + bool other_tbls_ok, bool exclude_index) +{ + if (exclude_index && + uses_index_fields_only(cond, table, keyno, other_tbls_ok)) + return 0; + + if (cond->type() == Item::COND_ITEM) + { + table_map tbl_map= 0; + if (((Item_cond*) cond)->functype() == Item_func::COND_AND_FUNC) + { + /* Create new top level AND item */ + Item_cond_and *new_cond= new (thd->mem_root) Item_cond_and(thd); + if (!new_cond) + return (COND*) 0; + List_iterator<Item> li(*((Item_cond*) cond)->argument_list()); + Item *item; + while ((item=li++)) + { + Item *fix= make_cond_remainder(thd, item, table, keyno, + other_tbls_ok, exclude_index); + if (fix) + { + new_cond->argument_list()->push_back(fix, thd->mem_root); + tbl_map |= fix->used_tables(); + } + } + switch (new_cond->argument_list()->elements) { + case 0: + return (COND*) 0; + case 1: + return new_cond->argument_list()->head(); + default: + new_cond->quick_fix_field(); + ((Item_cond*)new_cond)->used_tables_cache= tbl_map; + return new_cond; + } + } + else /* It's OR */ + { + Item_cond_or *new_cond= new (thd->mem_root) Item_cond_or(thd); + if (!new_cond) + return (COND*) 0; + List_iterator<Item> li(*((Item_cond*) cond)->argument_list()); + Item *item; + while ((item=li++)) + { + Item *fix= make_cond_remainder(thd, item, table, keyno, + other_tbls_ok, FALSE); + if (!fix) + return (COND*) 0; + new_cond->argument_list()->push_back(fix, thd->mem_root); + tbl_map |= fix->used_tables(); + } + new_cond->quick_fix_field(); + ((Item_cond*)new_cond)->used_tables_cache= tbl_map; + new_cond->top_level_item(); + return new_cond; + } + } + return cond; +} + + +/* + Try to extract and push the index condition + + SYNOPSIS + push_index_cond() + tab A join tab that has tab->table->file and its condition + in tab->select_cond + keyno Index for which extract and push the condition + + DESCRIPTION + Try to extract and push the index condition down to table handler +*/ + +void push_index_cond(JOIN_TAB *tab, uint keyno) +{ + DBUG_ENTER("push_index_cond"); + Item *idx_cond; + + /* + Backported the following from MySQL 5.6: + 6. The index is not a clustered index. The performance improvement + of pushing an index condition on a clustered key is much lower + than on a non-clustered key. This restriction should be + re-evaluated when WL#6061 is implemented. + */ + if ((tab->table->file->index_flags(keyno, 0, 1) & + HA_DO_INDEX_COND_PUSHDOWN) && + optimizer_flag(tab->join->thd, OPTIMIZER_SWITCH_INDEX_COND_PUSHDOWN) && + tab->join->thd->lex->sql_command != SQLCOM_UPDATE_MULTI && + tab->join->thd->lex->sql_command != SQLCOM_DELETE_MULTI && + tab->type != JT_CONST && tab->type != JT_SYSTEM && + !tab->table->file->is_clustering_key(keyno)) // 6 + { + DBUG_EXECUTE("where", + print_where(tab->select_cond, "full cond", QT_ORDINARY);); + + idx_cond= make_cond_for_index(tab->join->thd, tab->select_cond, tab->table, + keyno, tab->icp_other_tables_ok); + + DBUG_EXECUTE("where", + print_where(idx_cond, "idx cond", QT_ORDINARY);); + + if (idx_cond) + { + Item *idx_remainder_cond= 0; + tab->pre_idx_push_select_cond= tab->select_cond; + /* + For BKA cache we store condition to special BKA cache field + because evaluation of the condition requires additional operations + before the evaluation. This condition is used in + JOIN_CACHE_BKA[_UNIQUE]::skip_index_tuple() functions. + */ + if (tab->use_join_cache && + /* + if cache is used then the value is TRUE only + for BKA[_UNIQUE] cache (see check_join_cache_usage func). + */ + tab->icp_other_tables_ok && + (idx_cond->used_tables() & + ~(tab->table->map | tab->join->const_table_map))) + tab->cache_idx_cond= idx_cond; + else + { + idx_remainder_cond= tab->table->file->idx_cond_push(keyno, idx_cond); + + /* + If (1) there is an index condition that we couldn't push using ICP, + (2) we are using Join Buffering + (3) and we are using BKA + then use BKA's Index Condition Pushdown mechanism to check it. + */ + if (idx_remainder_cond && tab->use_join_cache && // (1) && (2) + tab->icp_other_tables_ok) // (3) + { + tab->cache_idx_cond= idx_remainder_cond; + idx_remainder_cond= NULL; + } + } + + /* + Disable eq_ref's "lookup cache" if we've pushed down an index + condition. + TODO: This check happens to work on current ICP implementations, but + there may exist a compliant implementation that will not work + correctly with it. Sort this out when we stabilize the condition + pushdown APIs. + */ + if (idx_remainder_cond != idx_cond) + tab->ref.disable_cache= TRUE; + + Item *row_cond= tab->idx_cond_fact_out ? + make_cond_remainder(tab->join->thd, tab->select_cond, + tab->table, keyno, + tab->icp_other_tables_ok, TRUE) : + tab->pre_idx_push_select_cond; + + DBUG_EXECUTE("where", + print_where(row_cond, "remainder cond", QT_ORDINARY);); + + if (row_cond) + { + if (!idx_remainder_cond) + tab->select_cond= row_cond; + else + { + COND *new_cond= new (tab->join->thd->mem_root) + Item_cond_and(tab->join->thd, row_cond, idx_remainder_cond); + tab->select_cond= new_cond; + tab->select_cond->quick_fix_field(); + ((Item_cond_and*)tab->select_cond)->used_tables_cache= + row_cond->used_tables() | idx_remainder_cond->used_tables(); + } + } + else + tab->select_cond= idx_remainder_cond; + if (tab->select) + { + DBUG_EXECUTE("where", + print_where(tab->select->cond, + "select_cond", + QT_ORDINARY);); + + tab->select->cond= tab->select_cond; + tab->select->pre_idx_push_select_cond= tab->pre_idx_push_select_cond; + } + } + } + DBUG_VOID_RETURN; +} + + |