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MWL#89: Cost-based choice between Materialization and IN->EXISTS transformation

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Phase 3: Implementation of re-optimization of subqueries with injected predicates
           and cost comparison between Materialization and IN->EXISTS strategies.

The commit contains the following known problems:
- The implementation of EXPLAIN has not been re-engineered to reflect the
  changes in subquery optimization. EXPLAIN for subqueries is called during
  the execute phase, which results in different code paths during JOIN::optimize
  and thus in differing EXPLAIN messages for constant/system tables.
- There are some valgrind warnings that need investigation
- Several EXPLAINs with minor differences need to be reconsidered after fixing
  the EXPLAIN problem above.

This patch also adds one extra optimizer_switch: 'in_to_exists' for complete
manual control of the subquery execution strategies.
This commit is contained in:
unknown
2010-09-30 18:32:44 +03:00
parent 50888477af
commit 8ec5e13f1f
12 changed files with 600 additions and 454 deletions
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15
sql/sql_select.h
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@ -1369,8 +1369,21 @@ inline bool sj_is_materialize_strategy(uint strategy)
class JOIN :public Sql_alloc
{
private:
JOIN(const JOIN &rhs); /**< not implemented */
JOIN& operator=(const JOIN &rhs); /**< not implemented */
protected:
/* Support for plan reoptimization with rewritten conditions. */
int reoptimize(Item *added_where, table_map join_tables,
POSITION *save_best_positions);
int save_query_plan(DYNAMIC_ARRAY *save_keyuse, POSITION *save_positions,
KEYUSE **save_join_tab_keyuse,
key_map *save_join_tab_checked_keys);
void restore_query_plan(DYNAMIC_ARRAY *save_keyuse, POSITION *save_positions,
KEYUSE **save_join_tab_keyuse,
key_map *save_join_tab_checked_keys);
public:
JOIN_TAB *join_tab,**best_ref;
JOIN_TAB **map2table; ///< mapping between table indexes and JOIN_TABs
@ -1746,7 +1759,7 @@ public:
NULL : join_tab+const_tables;
}
bool setup_subquery_caches();
bool choose_subquery_plan();
bool choose_subquery_plan(table_map join_tables);
private:
/**
TRUE if the query contains an aggregate function but has no GROUP