Subqueries: Inside-out execution for non-semijoin materialized subqueries that...

Subqueries: Inside-out execution for non-semijoin materialized subqueries that are AND-parts of the WHERE
- Code cleanup
- Query plan change is due to s/ha_rows JOIN_TAB::read_time/double JOIN_TAB::read_time/

mysql-test/r/subselect_mat.result

@@ -122,11 +122,11 @@ a1	a2
 explain extended
 select * from t1i where (a1, a2) in (select b1, b2 from t2i where b1 > '0' group by b1, b2);
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
-1	PRIMARY	SUBQUERY#2	ALL	distinct_key	#	#	#	3	100.00	#
-1	PRIMARY	t1i	ref	it1i1,it1i2,it1i3	#	#	#	1	100.00	#
+1	PRIMARY	t1i	index	it1i1,it1i2,it1i3	#	#	#	3	100.00	#
+1	PRIMARY	SUBQUERY#2	eq_ref	distinct_key	#	#	#	1	100.00	#
 2	SUBQUERY	t2i	range	it2i1,it2i3	#	#	#	3	100.00	#
 Warnings:
-Note	1003	select `test`.`t1i`.`a1` AS `a1`,`test`.`t1i`.`a2` AS `a2` from  <materialize> (select `test`.`t2i`.`b1` AS `b1`,`test`.`t2i`.`b2` AS `b2` from `test`.`t2i` where (`test`.`t2i`.`b1` > '0') group by `test`.`t2i`.`b1`,`test`.`t2i`.`b2`) join `test`.`t1i` where ((`test`.`t1i`.`a2` = `SUBQUERY#2`.`b2`) and (`test`.`t1i`.`a1` = `SUBQUERY#2`.`b1`))
+Note	1003	select `test`.`t1i`.`a1` AS `a1`,`test`.`t1i`.`a2` AS `a2` from  <materialize> (select `test`.`t2i`.`b1` AS `b1`,`test`.`t2i`.`b2` AS `b2` from `test`.`t2i` where (`test`.`t2i`.`b1` > '0') group by `test`.`t2i`.`b1`,`test`.`t2i`.`b2`) join `test`.`t1i` where ((`SUBQUERY#2`.`b2` = `test`.`t1i`.`a2`) and (`SUBQUERY#2`.`b1` = `test`.`t1i`.`a1`))
 select * from t1i where (a1, a2) in (select b1, b2 from t2i where b1 > '0' group by b1, b2);
 a1	a2
 1 - 01	2 - 01
@@ -134,11 +134,11 @@ a1	a2
 explain extended
 select * from t1i where (a1, a2) in (select b1, min(b2) from t2i where b1 > '0' group by b1);
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
-1	PRIMARY	SUBQUERY#2	ALL	distinct_key	#	#	#	3	100.00	#
-1	PRIMARY	t1i	ref	it1i1,it1i2,it1i3	#	#	#	1	100.00	#
+1	PRIMARY	t1i	index	it1i1,it1i2,it1i3	#	#	#	3	100.00	#
+1	PRIMARY	SUBQUERY#2	eq_ref	distinct_key	#	#	#	1	100.00	#
 2	SUBQUERY	t2i	range	it2i1,it2i3	#	#	#	3	100.00	#
 Warnings:
-Note	1003	select `test`.`t1i`.`a1` AS `a1`,`test`.`t1i`.`a2` AS `a2` from  <materialize> (select `test`.`t2i`.`b1` AS `b1`,min(`test`.`t2i`.`b2`) AS `min(b2)` from `test`.`t2i` where (`test`.`t2i`.`b1` > '0') group by `test`.`t2i`.`b1`) join `test`.`t1i` where ((`test`.`t1i`.`a2` = `SUBQUERY#2`.`min(b2)`) and (`test`.`t1i`.`a1` = `SUBQUERY#2`.`b1`))
+Note	1003	select `test`.`t1i`.`a1` AS `a1`,`test`.`t1i`.`a2` AS `a2` from  <materialize> (select `test`.`t2i`.`b1` AS `b1`,min(`test`.`t2i`.`b2`) AS `min(b2)` from `test`.`t2i` where (`test`.`t2i`.`b1` > '0') group by `test`.`t2i`.`b1`) join `test`.`t1i` where ((`SUBQUERY#2`.`min(b2)` = `test`.`t1i`.`a2`) and (`SUBQUERY#2`.`b1` = `test`.`t1i`.`a1`))
 select * from t1i where (a1, a2) in (select b1, min(b2) from t2i where b1 > '0' group by b1);
 a1	a2
 1 - 01	2 - 01

sql/item_subselect.cc

@@ -190,10 +190,6 @@ bool Item_subselect::fix_fields(THD *thd_param, Item **ref)
     changed= 1;
     inside_first_fix_fields= FALSE;
 
-
-    // all transformation is done (used by prepared statements)
-    changed= 1;
-
     /*
       Substitute the current item with an Item_in_optimizer that was
       created by Item_in_subselect::select_in_like_transformer and

sql/item_subselect.h

@@ -393,12 +393,12 @@ class Item_in_subselect :public Item_exists_subselect
     join->sj_subselects.
     jtbm-todo: option 1: let sj_subselects list pairs.
   */
-  bool convert_to_semi_join;
+  bool is_flattenable_semijoin;
   
   /*
     Cost to populate the temporary table (set on if-needed basis).
   */
-  double startup_cost;
+  //double startup_cost;
 
   bool *get_cond_guard(int i)
   {

sql/opt_range.cc

@@ -2285,7 +2285,8 @@ int SQL_SELECT::test_quick_select(THD *thd, key_map keys_to_use,
   quick=0;
   needed_reg.clear_all();
   quick_keys.clear_all();
-  if (keys_to_use.is_clear_all() || head->pos_in_table_list->jtbm_subselect)
+  DBUG_ASSERT(!head->is_filled_at_execution());
+  if (keys_to_use.is_clear_all() || head->is_filled_at_execution())
     DBUG_RETURN(0);
   records= head->file->stats.records;
   if (!records)

sql/opt_subselect.cc

@@ -172,7 +172,7 @@ int check_and_do_in_subquery_rewrites(JOIN *join)
       (void)subquery_types_allow_materialization(in_subs);
 
       in_subs->emb_on_expr_nest= thd->thd_marker.emb_on_expr_nest;
-      in_subs->convert_to_semi_join= TRUE; //JTBM
+      in_subs->is_flattenable_semijoin= TRUE;
 
       /* Register the subquery for further processing in flatten_subqueries() */
       select_lex->
@@ -240,7 +240,7 @@ int check_and_do_in_subquery_rewrites(JOIN *join)
             thd->thd_marker.emb_on_expr_nest == (TABLE_LIST*)0x1)
         {
           in_subs->emb_on_expr_nest= thd->thd_marker.emb_on_expr_nest;
-          in_subs->convert_to_semi_join= FALSE;
+          in_subs->is_flattenable_semijoin= FALSE;
           select_lex->outer_select()->
             join->sj_subselects.append(thd->mem_root, in_subs);
         }
@@ -358,7 +358,19 @@ bool subquery_types_allow_materialization(Item_in_subselect *in_subs)
 }
 
 
-static bool make_in_exists_conversion(THD *thd, JOIN *join, Item_in_subselect *item)
+/*
+  Finalize IN->EXISTS conversion in case we couldn't use materialization.
+
+  DESCRIPTION  Invoke the IN->EXISTS converter
+    Replace the Item_in_subselect with its wrapper Item_in_optimizer in WHERE.
+
+  RETURN 
+    FALSE - Ok
+    TRUE  - Fatal error
+*/
+
+static 
+bool make_in_exists_conversion(THD *thd, JOIN *join, Item_in_subselect *item)
 {
   DBUG_ENTER("make_in_exists_conversion");
   JOIN *child_join= item->unit->first_select()->join;
@@ -381,20 +393,15 @@ static bool make_in_exists_conversion(THD *thd, JOIN *join, Item_in_subselect *i
 
   Item *substitute= item->substitution;
   bool do_fix_fields= !item->substitution->fixed;
-  Item **tree= (item->emb_on_expr_nest == (TABLE_LIST*)1)?
-                 &join->conds : &(item->emb_on_expr_nest->on_expr);
-
-  Item *replace_me= item;
   /*
-    JTBM: the subquery was already mapped with Item_in_optimizer, so we
-    should search for that, not for original Item_in_subselect.
-    TODO: what about delaying that rewrite until here?
+    The Item_subselect has already been wrapped with Item_in_optimizer, so we
+    should search for item->optimizer, not 'item'.
   */
-  if (!item->convert_to_semi_join)
-  { //psergey-jtbm-fix: this branch is always taken??
-    replace_me= item->optimizer;
-  }
+  Item *replace_me= item->optimizer;
+  DBUG_ASSERT(replace_me==substitute);
 
+  Item **tree= (item->emb_on_expr_nest == (TABLE_LIST*)1)?
+                 &join->conds : &(item->emb_on_expr_nest->on_expr);
   if (replace_where_subcondition(join, tree, replace_me, substitute, 
                                  do_fix_fields))
     DBUG_RETURN(TRUE);
@@ -528,7 +535,7 @@ bool convert_join_subqueries_to_semijoins(JOIN *join)
        in_subq++)
   {
     bool remove_item= TRUE;
-    if ((*in_subq)->convert_to_semi_join) 
+    if ((*in_subq)->is_flattenable_semijoin) 
     {
       if (convert_subq_to_sj(join, *in_subq))
         DBUG_RETURN(TRUE);
@@ -548,7 +555,7 @@ bool convert_join_subqueries_to_semijoins(JOIN *join)
         should search for that, not for original Item_in_subselect.
         TODO: what about delaying that rewrite until here?
       */
-      if (!(*in_subq)->convert_to_semi_join)
+      if (!(*in_subq)->is_flattenable_semijoin)
       {
         replace_me= (*in_subq)->optimizer;
       }
@@ -593,7 +600,7 @@ bool convert_join_subqueries_to_semijoins(JOIN *join)
       should search for that, not for original Item_in_subselect.
       TODO: what about delaying that rewrite until here?
     */
-    if (!(*in_subq)->convert_to_semi_join)
+    if (!(*in_subq)->is_flattenable_semijoin)
     {
       replace_me= (*in_subq)->optimizer;
     }
@@ -622,9 +629,33 @@ bool convert_join_subqueries_to_semijoins(JOIN *join)
 }
 
 
-void get_temptable_params(Item_in_subselect *item, ha_rows *out_rows,
-                          ha_rows *scan_time)
+/*
+  Get #output_rows and scan_time estimates for a "delayed" table.
+
+  SYNOPSIS
+    get_delayed_table_estimates()
+      table         IN    Table to get estimates for
+      out_rows      OUT   E(#rows in the table)
+      scan_time     OUT   E(scan_time).
+      startup_cost  OUT   cost to populate the table.
+
+  DESCRIPTION
+    Get #output_rows and scan_time estimates for a "delayed" table. By
+    "delayed" here we mean that the table is filled at the start of query
+    execution. This means that the optimizer can't use table statistics to 
+    get #rows estimate for it, it has to call this function instead.
+
+    This function is expected to make different actions depending on the nature
+    of the table. At the moment there is only one kind of delayed tables,
+    non-flattenable semi-joins.
+*/
+
+void get_delayed_table_estimates(TABLE *table,
+                                 ha_rows *out_rows, 
+                                 double *scan_time,
+                                 double *startup_cost)
 {
+  Item_in_subselect *item= table->pos_in_table_list->jtbm_subselect;
   item->optimize();
 
   DBUG_ASSERT(item->engine->engine_type() ==
@@ -644,7 +675,7 @@ void get_temptable_params(Item_in_subselect *item, ha_rows *out_rows,
     read_time += join->best_positions[i].read_time;
   }
   *out_rows= rows;
-  item->startup_cost= read_time;
+  *startup_cost= read_time;
   /* Calculate cost of scanning the temptable */
   double data_size= rows * hash_sj_engine->tmp_table->s->reclength;
   /* Do like in handler::read_time */

sql/opt_subselect.h

@@ -367,8 +367,10 @@ int clear_sj_tmp_tables(JOIN *join);
 int rewrite_to_index_subquery_engine(JOIN *join);
 
 
-void get_temptable_params(Item_in_subselect *item, ha_rows *out_rows,
-                          ha_rows *scan_time);
+void get_delayed_table_estimates(TABLE *table,
+                                 ha_rows *out_rows, 
+                                 double *scan_time,
+                                 double *startup_cost);
 
 bool do_jtbm_materialization_if_needed(JOIN_TAB *tab);
 

sql/sql_select.cc

@@ -2581,10 +2581,10 @@ make_join_statistics(JOIN *join, TABLE_LIST *tables_arg, COND *conds,
     {
       /* s is the only inner table of an outer join */
 #ifdef WITH_PARTITION_STORAGE_ENGINE
-      if (!table->pos_in_table_list->jtbm_subselect &&
+      if (!table->is_filled_at_execution() &&
            (!table->file->stats.records || table->no_partitions_used) && !embedding)
 #else
-      if (!table->pos_in_table_list->jtbm_subselect &&
+      if (!table->is_filled_at_execution() &&
           !table->file->stats.records && !embedding)
 #endif
       {						// Empty table
@@ -2619,7 +2619,7 @@ make_join_statistics(JOIN *join, TABLE_LIST *tables_arg, COND *conds,
 #else
     const bool no_partitions_used= FALSE;
 #endif
-    if (!table->pos_in_table_list->jtbm_subselect && 
+    if (!table->is_filled_at_execution() && 
         (table->s->system || table->file->stats.records <= 1 ||
          no_partitions_used) &&
 	!s->dependent &&
@@ -2719,7 +2719,7 @@ make_join_statistics(JOIN *join, TABLE_LIST *tables_arg, COND *conds,
     {
       table=s->table;
 
-      if (table->pos_in_table_list->jtbm_subselect)
+      if (table->is_filled_at_execution())
         continue;
 
       /* 
@@ -2874,6 +2874,7 @@ make_join_statistics(JOIN *join, TABLE_LIST *tables_arg, COND *conds,
 
   for (s=stat ; s < stat_end ; s++)
   {
+    s->startup_cost= 0;
     if (s->type == JT_SYSTEM || s->type == JT_CONST)
     {
       /* Only one matching row */
@@ -2882,18 +2883,17 @@ make_join_statistics(JOIN *join, TABLE_LIST *tables_arg, COND *conds,
     }
     /* Approximate found rows and time to read them */
 
-    if (s->table->pos_in_table_list->jtbm_subselect)
+    if (s->table->is_filled_at_execution())
     {
-       get_temptable_params(s->table->pos_in_table_list->jtbm_subselect,
-                            &s->records,
-                            &s->read_time);
+      get_delayed_table_estimates(s->table, &s->records, &s->read_time,
+                                  &s->startup_cost);
       s->found_records= s->records;
       table->quick_condition_rows=s->records;
     }
     else
     {
-      s->found_records=s->records=s->table->file->stats.records;
-      s->read_time=(ha_rows) s->table->file->scan_time();
+      s->found_records= s->records= s->table->file->stats.records;
+      s->read_time= s->table->file->scan_time();
     }
 
 
@@ -2922,7 +2922,7 @@ make_join_statistics(JOIN *join, TABLE_LIST *tables_arg, COND *conds,
         (!s->table->pos_in_table_list->embedding ||               // (2)
          (s->table->pos_in_table_list->embedding &&               // (3)
           s->table->pos_in_table_list->embedding->sj_on_expr)) && // (3)
-        !s->table->pos_in_table_list->jtbm_subselect)
+        !s->table->is_filled_at_execution())
     {
       ha_rows records;
       SQL_SELECT *select;
@@ -2960,7 +2960,7 @@ make_join_statistics(JOIN *join, TABLE_LIST *tables_arg, COND *conds,
       if (records != HA_POS_ERROR)
       {
 	s->found_records=records;
-	s->read_time= (ha_rows) (s->quick ? s->quick->read_time : 0.0);
+	s->read_time= s->quick ? s->quick->read_time : 0.0;
       }
       delete select;
     }
@@ -4288,7 +4288,6 @@ best_access_path(JOIN      *join,
   ha_rows rec;
   bool best_uses_jbuf= FALSE;
   Item_in_subselect* jtbm_subselect= s->table->pos_in_table_list->jtbm_subselect;
-  bool jtbm_ref_used= FALSE;
 
   Loose_scan_opt loose_scan_opt;
   DBUG_ENTER("best_access_path");
@@ -4641,8 +4640,8 @@ best_access_path(JOIN      *join,
           else
             tmp= best_time;                    // Do nothing
         }
-        if (jtbm_subselect)
-          tmp += jtbm_subselect->startup_cost;
+
+        tmp += s->startup_cost;
         loose_scan_opt.check_ref_access_part2(key, start_key, records, tmp);
       } /* not ft_key */
       if (tmp < best_time - records/(double) TIME_FOR_COMPARE)
@@ -4653,8 +4652,6 @@ best_access_path(JOIN      *join,
         best_key= start_key;
         best_max_key_part= max_key_part;
         best_ref_depends_map= found_ref;
-        if (jtbm_subselect)
-          jtbm_ref_used= TRUE;
       }
     } /* for each key */
     records= best_records;
@@ -4687,6 +4684,11 @@ best_access_path(JOIN      *join,
         Since we have a 'ref' access path, and FORCE INDEX instructs us to
         choose it over ALL/index, there is no need to consider a full table
         scan.
+    (5) Non-flattenable semi-joins: don't consider doing a scan of temporary
+        table if we had an option to make lookups into it. In real-world cases,
+        lookups are cheaper than full scans, but when the table is small, they
+        can be [considered to be] more expensive, which causes lookups not to 
+        be used for cases with small datasets, which is annoying.
   */
   if ((records >= s->found_records || best > s->read_time) &&            // (1)
       !(s->quick && best_key && s->quick->index == best_key->key &&      // (2)
@@ -4694,7 +4696,7 @@ best_access_path(JOIN      *join,
       !((s->table->file->ha_table_flags() & HA_TABLE_SCAN_ON_INDEX) &&   // (3)
         ! s->table->covering_keys.is_clear_all() && best_key && !s->quick) &&// (3)
       !(s->table->force_index && best_key && !s->quick) &&               // (4)
-      !jtbm_ref_used)            
+      !(best_key && jtbm_subselect))                                     // (5)
   {                                             // Check full join
     ha_rows rnd_records= s->found_records;
     /*
@@ -4741,12 +4743,19 @@ best_access_path(JOIN      *join,
     }
     else
     {
+#if 0      
       /* Estimate cost of reading table. */
-      if (jtbm_subselect)
+      if (jtbm_subselect) //psergey-jtbm-todo: why the difference?
         tmp= s->read_time;
       else
         tmp= s->table->file->scan_time();
-
+      //psergey-debug:
+      if (!jtbm_subselect && fabs(s->read_time - s->table->file->scan_time()) > 1.0)
+      {
+        fprintf(stderr, "Q:%s\n", thd->query());
+      }
+#endif
+      tmp= s->read_time;
       if ((s->table->map & join->outer_join) || disable_jbuf)     // Can't use join cache
       {
         /*
@@ -4775,8 +4784,7 @@ best_access_path(JOIN      *join,
       }
     }
 
-    if (jtbm_subselect)
-      tmp += jtbm_subselect->startup_cost;
+    tmp += s->startup_cost;
     /*
       We estimate the cost of evaluating WHERE clause for found records
       as record_count * rnd_records / TIME_FOR_COMPARE. This cost plus
@@ -6722,12 +6730,12 @@ make_join_select(JOIN *join,SQL_SELECT *select,COND *cond)
 	    the index if we are using limit and this is the first table
 	  */
 
-	  if ((cond &&
-               (!tab->keys.is_subset(tab->const_keys) && i > 0)) ||
+	  if (!tab->table->is_filled_at_execution() &&
+              ((cond && (!tab->keys.is_subset(tab->const_keys) && i > 0)) ||
                (!tab->const_keys.is_clear_all() && i == join->const_tables &&
                 join->unit->select_limit_cnt <
                 join->best_positions[i].records_read &&
-	       !(join->select_options & OPTION_FOUND_ROWS)))
+                !(join->select_options & OPTION_FOUND_ROWS))))
 	  {
 	    /* Join with outer join condition */
 	    COND *orig_cond=sel->cond;

sql/sql_select.h

@@ -210,7 +210,10 @@ typedef struct st_join_table {
     method (but not 'index' for some reason), i.e. this matches method which
     E(#records) is in found_records.
   */
-  ha_rows       read_time;
+  double        read_time;
+  
+  /* Startup cost for execution */
+  double        startup_cost;
 
   table_map	dependent,key_dependent;
   uint		use_quick,index;

sql/table.cc

@@ -5114,6 +5114,12 @@ bool st_table::is_children_attached(void)
          (parent && parent->children_attached));
 }
 
+
+bool st_table::is_filled_at_execution()
+{ 
+  return test(pos_in_table_list->jtbm_subselect);
+}
+
 /*
   Cleanup this table for re-execution.
 

sql/table.h

@@ -914,6 +914,13 @@ struct st_table {
   inline bool needs_reopen_or_name_lock()
   { return s->version != refresh_version; }
   bool is_children_attached(void);
+ 
+  /*
+    If TRUE, the table is filled at execution phase (and so, the optimizer 
+    should not do things like range analysis or constant table detection on
+    it).
+  */
+  bool is_filled_at_execution();
 };
 
 enum enum_schema_table_state