MWL#89

  
- Post-review fixes. Intermediate commit to address review point 1.6.
- Fixed valgrind warnings

sql/opt_subselect.cc

@@ -3653,8 +3653,8 @@ bool JOIN::optimize_unflattened_subqueries()
 */
 
 bool JOIN::choose_subquery_plan(table_map join_tables)
-{  /* The original QEP of the subquery. */
-  Query_plan_state save_qep;
+{
+  Query_plan_state save_qep; /* The original QEP of the subquery. */
   enum_reopt_result reopt_result= REOPT_NONE;
   Item_in_subselect *in_subs;
 
@@ -3681,32 +3681,50 @@ bool JOIN::choose_subquery_plan(table_map join_tables)
   if (in_subs->in_strategy & SUBS_MATERIALIZATION &&
       in_subs->in_strategy & SUBS_IN_TO_EXISTS)
   {
-    JOIN *outer_join= unit->outer_select() ? unit->outer_select()->join : NULL;
+    JOIN *outer_join;
     JOIN *inner_join= this;
-    /* Cost of the outer JOIN. */
-    double outer_read_time, outer_record_count;
-    /* Cost of the unmodified subquery. */
+    /* Number of (partial) rows of the outer JOIN filtered by the IN predicate. */
+    double outer_record_count;
+    /* 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, inner_record_count_2;
+    /* Cost and row count 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)
     {
+      uint outer_partial_plan_len;
       /*
         Make_cond_for_table is called for predicates only in the WHERE/ON
         clauses. In all other cases, predicates are not pushed to any
         JOIN_TAB, and their joi_tab_idx remains MAX_TABLES. Such predicates
-        are evaluated for each complete row.
+        are evaluated for each complete row of the outer join.
       */
-      uint partial_plan_len= (in_subs->get_join_tab_idx() == MAX_TABLES) ?
-                             outer_join->tables :
-                             in_subs->get_join_tab_idx() + 1;
-      outer_join->get_partial_join_cost(partial_plan_len,
-                                        &outer_read_time, &outer_record_count);
+      outer_partial_plan_len= (in_subs->get_join_tab_idx() == MAX_TABLES) ?
+                               outer_join->tables :
+                               in_subs->get_join_tab_idx() + 1;
+      outer_join->get_partial_join_cost(outer_partial_plan_len, &dummy,
+                                        &outer_record_count);
+      if (outer_join->tables > outer_join->const_tables)
+        outer_lookup_keys= prev_record_reads(outer_join->best_positions,
+                                             outer_partial_plan_len,
+                                             in_subs->used_tables());
+      else
+      {
+        /* If all tables are constant, positions is undefined. */
+        outer_lookup_keys= 1;
+      }
     }
     else
     {
@@ -3714,15 +3732,17 @@ bool JOIN::choose_subquery_plan(table_map join_tables)
         TODO: outer_join can be NULL for DELETE statements.
         How to compute its cost?
       */
-      outer_read_time= 1; /* TODO */
-      outer_record_count= 1;  /* TODO */
+      outer_record_count= 1;
+      outer_lookup_keys=1;
     }
+    DBUG_ASSERT(outer_lookup_keys <= outer_record_count);
 
-    inner_join->get_partial_join_cost(inner_join->tables,
-                                      &inner_read_time_1,
-                                      &inner_record_count_1);
-    /* inner_read_time_1 above is a dummy, get the correct total join cost. */
+    /*
+      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 != tables)
     {
@@ -3734,9 +3754,6 @@ bool JOIN::choose_subquery_plan(table_map join_tables)
       if (reopt_result == REOPT_ERROR)
         return TRUE;
 
-      inner_join->get_partial_join_cost(inner_join->tables,
-                                        &inner_read_time_2,
-                                        &inner_record_count_2);
       /* inner_read_time_2 above is a dummy, get the correct total join cost. */
       inner_read_time_2= inner_join->best_read;
 
@@ -3745,13 +3762,12 @@ bool JOIN::choose_subquery_plan(table_map join_tables)
     {
       /* Reoptimization would not produce any better plan. */
       inner_read_time_2= inner_read_time_1;
-      inner_record_count_2= inner_record_count_1;
     }
 
-    /* Compute execution costs. */
     /*
-      1. Compute the cost of the materialization strategy.
+      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);
     /* The cost of writing one row into the temporary table. */
     double write_cost= get_tmp_table_write_cost(thd, inner_record_count_1,
@@ -3769,12 +3785,10 @@ bool JOIN::choose_subquery_plan(table_map join_tables)
     materialize_strategy_cost= materialization_cost +
                                outer_record_count * lookup_cost;
 
-    /*
-      2. Compute the cost of the IN=>EXISTS strategy.
-    */
-    in_exists_strategy_cost= outer_record_count * inner_read_time_2;
+    /* C.2 Compute the cost of the IN=>EXISTS strategy. */
+    in_exists_strategy_cost= outer_lookup_keys * inner_read_time_2;
 
-    /* Compare the costs and choose the cheaper strategy. */
+    /* C.3 Compare the costs and choose the cheaper strategy. */
     if (materialize_strategy_cost >= in_exists_strategy_cost)
       in_subs->in_strategy&= ~SUBS_MATERIALIZATION;
     else

sql/sql_select.cc

@@ -65,15 +65,13 @@ static bool sort_and_filter_keyuse(DYNAMIC_ARRAY *keyuse);
 static int sort_keyuse(KEYUSE *a,KEYUSE *b);
 static bool create_ref_for_key(JOIN *join, JOIN_TAB *j, KEYUSE *org_keyuse,
 			       table_map used_tables);
-bool choose_plan(JOIN *join,table_map join_tables);
-
 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 void optimize_straight_join(JOIN *join, table_map join_tables);
 static bool greedy_search(JOIN *join, table_map remaining_tables,
-                             uint depth, uint prune_level);
+                          uint depth, uint prune_level);
 static bool best_extension_by_limited_search(JOIN *join,
                                              table_map remaining_tables,
                                              uint idx, double record_count,
@@ -90,7 +88,6 @@ static int join_tab_cmp_embedded_first(const void *emb, const void* ptr1, const
 static bool find_best(JOIN *join,table_map rest_tables,uint index,
 		      double record_count,double read_time);
 static uint cache_record_length(JOIN *join,uint index);
-static double prev_record_reads(JOIN *join, uint idx, table_map found_ref);
 static bool get_best_combination(JOIN *join);
 static store_key *get_store_key(THD *thd,
 				KEYUSE *keyuse, table_map used_tables,
@@ -3143,6 +3140,7 @@ make_join_statistics(JOIN *join, TABLE_LIST *tables_arg, COND *conds,
   {
     memcpy((uchar*) join->best_positions,(uchar*) join->positions,
 	   sizeof(POSITION)*join->const_tables);
+    join->record_count= 1.0;
     join->best_read=1.0;
   }
   if (join->choose_subquery_plan(all_table_map & ~join->const_table_map))
@@ -4505,8 +4503,8 @@ best_access_path(JOIN      *join,
             if (!(keyuse->used_tables & ~join->const_table_map))
               const_part|= keyuse->keypart_map;
 
-            double tmp2= prev_record_reads(join, idx, (found_ref |
-                                                      keyuse->used_tables));
+            double tmp2= prev_record_reads(join->positions, idx,
+                                           (found_ref | keyuse->used_tables));
             if (tmp2 < best_prev_record_reads)
             {
               best_part_found_ref= keyuse->used_tables & ~join->const_table_map;
@@ -4546,7 +4544,7 @@ best_access_path(JOIN      *join,
           Really, there should be records=0.0 (yes!)
           but 1.0 would be probably safer
         */
-        tmp= prev_record_reads(join, idx, found_ref);
+        tmp= prev_record_reads(join->positions, idx, found_ref);
         records= 1.0;
       }
       else
@@ -4561,7 +4559,7 @@ best_access_path(JOIN      *join,
           max_key_part= (uint) ~0;
           if ((keyinfo->flags & (HA_NOSAME | HA_NULL_PART_KEY)) == HA_NOSAME)
           {
-            tmp = prev_record_reads(join, idx, found_ref);
+            tmp = prev_record_reads(join->positions, idx, found_ref);
             records=1.0;
           }
           else
@@ -5275,6 +5273,7 @@ optimize_straight_join(JOIN *join, table_map join_tables)
     read_time+= record_count;  // We have to make a temp table
   memcpy((uchar*) join->best_positions, (uchar*) join->positions,
          sizeof(POSITION)*idx);
+  join->record_count= record_count;
   join->best_read= read_time;
 }
 
@@ -5487,7 +5486,7 @@ void JOIN::get_partial_join_cost(uint n_tables,
   double record_count= 1;
   double read_time= 0.0;
 
-  DBUG_ASSERT(n_tables <= tables && n_tables > 0);
+  DBUG_ASSERT(n_tables <= tables);
 
   for (uint i= const_tables; i < n_tables; i++)
   {
@@ -5502,8 +5501,6 @@ void JOIN::get_partial_join_cost(uint n_tables,
 }
 
 
-
-
 /**
   Find a good, possibly optimal, query execution plan (QEP) by a possibly
   exhaustive search.
@@ -5756,6 +5753,7 @@ best_extension_by_limited_search(JOIN      *join,
         {
           memcpy((uchar*) join->best_positions, (uchar*) join->positions,
                  sizeof(POSITION) * (idx + 1));
+          join->record_count= current_record_count;
           join->best_read= current_read_time - 0.001;
         }
         DBUG_EXECUTE("opt", print_plan(join, idx+1,
@@ -5981,12 +5979,12 @@ cache_record_length(JOIN *join,uint idx)
     Expected number of row combinations
 */
 
-static double
-prev_record_reads(JOIN *join, uint idx, table_map found_ref)
+double
+prev_record_reads(POSITION *positions, uint idx, table_map found_ref)
 {
   double found=1.0;
-  POSITION *pos_end= join->positions - 1;
-  for (POSITION *pos= join->positions + idx - 1; pos != pos_end; pos--)
+  POSITION *pos_end= positions - 1;
+  for (POSITION *pos= positions + idx - 1; pos != pos_end; pos--)
   {
     if (pos->table->table->map & found_ref)
     {
@@ -19478,7 +19476,10 @@ JOIN::reoptimize(Item *added_where, table_map join_tables,
   }
 
   if (!added_keyuse.elements)
+  {
+    delete_dynamic(&added_keyuse);
     return REOPT_OLD_PLAN;
+  }
 
   if (save_to)
     save_query_plan(save_to);

sql/sql_select.h

@@ -1376,7 +1376,8 @@ private:
 protected:
 
   /**
-    ???
+    The subset of the state of a JOIN that represents an optimized query
+    execution plan. Allows saving/restoring different plans for the same query.
   */
   class Query_plan_state {
   public:
@@ -1512,6 +1513,13 @@ public:
     account the changes made by test_if_skip_sort_order()).
   */
   double   best_read;
+  /*
+    Estimated result rows (fanout) of the whole query. If this is a subquery
+    that is reexecuted multiple times, this value includes the estiamted # of
+    reexecutions. This value is equal to the multiplication of all
+    join->positions[i].records_read of a JOIN.
+  */
+  double   record_count;
   List<Item> *fields;
   List<Cached_item> group_fields, group_fields_cache;
   TABLE    *tmp_table;
@@ -2054,7 +2062,7 @@ inline Item * and_items(Item* cond, Item *item)
 {
   return (cond? (new Item_cond_and(cond, item)) : item);
 }
-bool choose_plan(JOIN *join,table_map join_tables);
+bool choose_plan(JOIN *join, table_map join_tables);
 void optimize_wo_join_buffering(JOIN *join, uint first_tab, uint last_tab, 
                                 table_map last_remaining_tables, 
                                 bool first_alt, uint no_jbuf_before,
@@ -2099,5 +2107,6 @@ bool create_internal_tmp_table(TABLE *table, KEY *keyinfo,
                                ulonglong options);
 bool open_tmp_table(TABLE *table);
 void setup_tmp_table_column_bitmaps(TABLE *table, uchar *bitmaps);
+double prev_record_reads(POSITION *positions, uint idx, table_map found_ref);
 
 #endif /* SQL_SELECT_INCLUDED */