Fixed bug mdev-5191.

Corrected cost estimates when a join buffer is used and the optimizer is requested
to use condition selectivities.

mysql-test/r/subselect_sj_mat.result

@@ -94,7 +94,7 @@ a1	a2
 explain extended
 select * from t1i where a1 in (select b1 from t2i where b1 > '0');
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
-1	PRIMARY	t2i	index	it2i1,it2i3	it2i1	#	NULL	5	40.00	Using where; Using index; LooseScan
+1	PRIMARY	t2i	index	it2i1,it2i3	it2i1	#	NULL	5	50.00	Using where; Using index; LooseScan
 1	PRIMARY	t1i	ref	_it1_idx	_it1_idx	#	_ref_	1	100.00	
 Warnings:
 Note	1003	select `test`.`t1i`.`a1` AS `a1`,`test`.`t1i`.`a2` AS `a2` from `test`.`t1i` semi join (`test`.`t2i`) where ((`test`.`t1i`.`a1` = `test`.`t2i`.`b1`) and (`test`.`t2i`.`b1` > '0'))
@@ -117,7 +117,7 @@ a1	a2
 explain extended
 select * from t1i where (a1, a2) in (select b1, b2 from t2i where b1 > '0');
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
-1	PRIMARY	t2i	index	it2i1,it2i2,it2i3	it2i3	#	NULL	5	40.00	Using where; Using index; LooseScan
+1	PRIMARY	t2i	index	it2i1,it2i2,it2i3	it2i3	#	NULL	5	50.00	Using where; Using index; LooseScan
 1	PRIMARY	t1i	ref	_it1_idx	_it1_idx	#	_ref_	1	100.00	
 Warnings:
 Note	1003	select `test`.`t1i`.`a1` AS `a1`,`test`.`t1i`.`a2` AS `a2` from `test`.`t1i` semi join (`test`.`t2i`) where ((`test`.`t1i`.`a1` = `test`.`t2i`.`b1`) and (`test`.`t1i`.`a2` = `test`.`t2i`.`b2`) and (`test`.`t2i`.`b1` > '0'))
@@ -319,7 +319,7 @@ where (a1, a2) in (select b1, b2 from t2i where b1 >  '0') and
 (a1, a2) in (select c1, c2 from t3i
 where (c1, c2) in (select b1, b2 from t2i where b2 > '0'));
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
-1	PRIMARY	t2i	index	it2i1,it2i2,it2i3	#	#	#	5	40.00	#
+1	PRIMARY	t2i	index	it2i1,it2i2,it2i3	#	#	#	5	50.00	#
 1	PRIMARY	t1i	ref	it1i1,it1i2,it1i3	#	#	#	1	100.00	#
 1	PRIMARY	t3i	ref	it3i1,it3i2,it3i3	#	#	#	1	100.00	#
 1	PRIMARY	t2i	ref	it2i1,it2i2,it2i3	#	#	#	2	100.00	#
@@ -407,7 +407,7 @@ id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
 2	MATERIALIZED	t2	ALL	NULL	#	#	#	5	100.00	#
 4	MATERIALIZED	t3	ALL	NULL	#	#	#	4	100.00	#
 3	MATERIALIZED	t3	ALL	NULL	#	#	#	4	100.00	#
-7	UNION	t2i	index	it2i1,it2i2,it2i3	#	#	#	5	40.00	#
+7	UNION	t2i	index	it2i1,it2i2,it2i3	#	#	#	5	50.00	#
 7	UNION	t1i	ref	it1i1,it1i2,it1i3	#	#	#	1	100.00	#
 7	UNION	t3i	ref	it3i1,it3i2,it3i3	#	#	#	1	100.00	#
 7	UNION	t2i	ref	it2i1,it2i2,it2i3	#	#	#	2	100.00	#

mysql-test/t/selectivity.test

@@ -739,3 +739,58 @@ DROP TABLE t1,t2,t3;
 
 set use_stat_tables=@save_use_stat_tables;
 
+--echo #
+--echo # Bug mdev-5191: performance degradation due to a suboptimal chosen plan   
+--echo #                when optimizer_use_condition_selectivity=3
+--echo #
+
+set use_stat_tables = 'preferably';
+
+set @@RAND_SEED1=810763568, @@RAND_SEED2=600681772;
+set TIMESTAMP=1394806993;
+
+create table t1 (a int, b int) engine=myisam;
+insert t1 values (rand()*1e5, rand()*1e5);
+insert t1 select rand()*1e5, rand()*1e5 from t1;
+insert t1 select rand()*1e5, rand()*1e5 from t1;
+insert t1 select rand()*1e5, rand()*1e5 from t1;
+insert t1 select rand()*1e5, rand()*1e5 from t1;
+insert t1 select rand()*1e5, rand()*1e5 from t1;
+insert t1 select rand()*1e5, rand()*1e5 from t1;
+insert t1 select rand()*1e5, rand()*1e5 from t1;
+insert t1 select rand()*1e5, rand()*1e5 from t1;
+insert t1 select rand()*1e5, rand()*1e5 from t1;
+insert t1 select rand()*1e5, rand()*1e5 from t1;
+insert t1 select rand()*1e5, rand()*1e5 from t1;
+insert t1 select rand()*1e5, rand()*1e5 from t1;
+insert t1 select rand()*1e5, rand()*1e5 from t1;
+insert t1 select rand()*1e5, rand()*1e5 from t1;
+insert t1 select rand()*1e5, rand()*1e5 from t1;
+insert t1 select rand()*1e5, rand()*1e5 from t1;
+insert t1 select rand()*1e5, rand()*1e5 from t1;
+insert t1 select rand()*1e5, rand()*1e5 from t1;
+
+create table t2 (c int, d int, key(c), key(d)) engine=myisam;
+insert t2 select floor(rand()*1e5/2)*2, floor(rand()*1e5/3)*3 from t1;
+
+analyze table t1,t2;
+
+set optimizer_use_condition_selectivity=1;
+explain extended 
+select * from t1, t2, t1 as t3
+  where t1.b=t2.c and t2.d=t3.a and t3.b<5 and t1.a < 2000;
+select * from t1, t2, t1 as t3
+  where t1.b=t2.c and t2.d=t3.a and t3.b<5 and t1.a < 2000;
+
+set optimizer_use_condition_selectivity=3;
+explain extended
+select * from t1, t2, t1 as t3
+  where t1.b=t2.c and t2.d=t3.a and t3.b<5 and t1.a < 2000;
+select * from t1, t2, t1 as t3
+  where t1.b=t2.c and t2.d=t3.a and t3.b<5 and t1.a < 2000;
+
+set optimizer_use_condition_selectivity=@save_optimizer_use_condition_selectivity;
+
+drop table t1,t2;
+
+set use_stat_tables=@save_use_stat_tables;

sql/sql_select.cc

@@ -5565,9 +5565,23 @@ void set_position(JOIN *join,uint idx,JOIN_TAB *table,KEYUSE *key)
 /* Estimate of the number matching candidates in the joined table */
 
 inline
-ha_rows matching_candidates_in_table(JOIN_TAB *s, bool with_found_constraint)
+double matching_candidates_in_table(JOIN_TAB *s, bool with_found_constraint,
+                                     uint use_cond_selectivity)
 {
-  ha_rows records= s->found_records;
+  ha_rows records;
+  double dbl_records;
+
+  if (use_cond_selectivity > 1)
+  {
+    TABLE *table= s->table;
+    double sel= table->cond_selectivity;
+    double table_records= table->stat_records();
+    dbl_records= table_records * sel;
+    return dbl_records;
+  }
+
+  records = s->found_records;
+
   /*
     If there is a filtering condition on the table (i.e. ref analyzer found
     at least one "table.keyXpartY= exprZ", where exprZ refers only to tables
@@ -5587,7 +5601,8 @@ ha_rows matching_candidates_in_table(JOIN_TAB *s, bool with_found_constraint)
   if (s->table->quick_condition_rows != s->found_records)
     records= s->table->quick_condition_rows;
 
-  return records;
+  dbl_records= records;
+  return dbl_records;
 }
 
 
@@ -5630,6 +5645,7 @@ best_access_path(JOIN      *join,
                  POSITION *loose_scan_pos)
 {
   THD *thd= join->thd;
+  uint use_cond_selectivity= thd->variables.optimizer_use_condition_selectivity;
   KEYUSE *best_key=         0;
   uint best_max_key_part=   0;
   my_bool found_constraint= 0;
@@ -6061,7 +6077,8 @@ best_access_path(JOIN      *join,
   {
     double join_sel= 0.1;
     /* Estimate the cost of  the hash join access to the table */
-    ha_rows rnd_records= matching_candidates_in_table(s, found_constraint);
+    double rnd_records= matching_candidates_in_table(s, found_constraint,
+                                                     use_cond_selectivity);
 
     tmp= s->quick ? s->quick->read_time : s->scan_time();
     tmp+= (s->records - rnd_records)/(double) TIME_FOR_COMPARE;
@@ -6073,7 +6090,7 @@ best_access_path(JOIN      *join,
     best_time= tmp + 
                (record_count*join_sel) / TIME_FOR_COMPARE * rnd_records;
     best= tmp;
-    records= rows2double(rnd_records);
+    records= rnd_records;
     best_key= hj_start_key;
     best_ref_depends_map= 0;
     best_uses_jbuf= TRUE;
@@ -6120,7 +6137,8 @@ best_access_path(JOIN      *join,
       !(s->table->force_index && best_key && !s->quick) &&               // (4)
       !(best_key && s->table->pos_in_table_list->jtbm_subselect))        // (5)
   {                                             // Check full join
-    ha_rows rnd_records= matching_candidates_in_table(s, found_constraint);
+    double rnd_records= matching_candidates_in_table(s, found_constraint,
+                                                      use_cond_selectivity);
 
     /*
       Range optimizer never proposes a RANGE if it isn't better
@@ -6193,7 +6211,7 @@ best_access_path(JOIN      *join,
         will ensure that this will be used
       */
       best= tmp;
-      records= rows2double(rnd_records);
+      records= rnd_records;
       best_key= 0;
       /* range/index_merge/ALL/index access method are "independent", so: */
       best_ref_depends_map= 0;
@@ -7298,6 +7316,10 @@ double table_cond_selectivity(JOIN *join, uint idx, JOIN_TAB *s,
       keyuse++;
     } while (keyuse->table == table && keyuse->key == key);
   }
+  else
+  {
+    sel= 1;
+  }
     
   /* 
     If the field f from the table is equal to a field from one the
@@ -8312,7 +8334,7 @@ get_best_combination(JOIN *join)
       Save records_read in JOIN_TAB so that select_describe()/etc don't have
       to access join->best_positions[]. 
     */
-    j->records_read= (ha_rows)join->best_positions[tablenr].records_read;
+    j->records_read= join->best_positions[tablenr].records_read;
     j->cond_selectivity= join->best_positions[tablenr].cond_selectivity;
     join->map2table[j->table->tablenr]= j;
 

sql/sql_select.h

@@ -296,8 +296,7 @@ typedef struct st_join_table {
   */
   double        read_time;
   
-  /* psergey-todo: make the below have type double, like POSITION::records_read? */
-  ha_rows       records_read;
+  double        records_read;
   
   /* The selectivity of the conditions that can be pushed to the table */ 
   double        cond_selectivity;