Fixed an incorrect calculation of JOIN_CACHE::max_buff_size.

mysql-test/r/subselect_sj_jcl6.result

@@ -723,7 +723,6 @@ WHERE int_nokey IN (SELECT it2.int_key
 FROM it1 LEFT JOIN it2 ON it2.datetime_key);
 int_key
 0
-8
 2
 0
 7
@@ -734,10 +733,11 @@ int_key
 0
 0
 0
-0
 3
 7
 7
+8
+0
 5
 EXPLAIN
 SELECT int_key FROM ot1

sql/sql_join_cache.cc

@@ -747,7 +747,7 @@ ulong JOIN_CACHE::get_max_join_buffer_size()
     if (join_tab->join_buffer_size_limit)
       set_if_smaller(limit_sz, join_tab->join_buffer_size_limit);
     if (limit_sz / max_records > space_per_record)
-      max_sz*= space_per_record * max_records;
+      max_sz= space_per_record * max_records;
     else
       max_sz= limit_sz;
     max_sz+= pack_length_with_blob_ptrs;
@@ -790,15 +790,18 @@ int JOIN_CACHE::alloc_buffer()
 {
   JOIN_TAB *tab;
   JOIN_CACHE *cache;
+  uint i= join->const_tables;
   ulonglong curr_buff_space_sz= 0;
   ulonglong curr_min_buff_space_sz= 0;
   ulonglong join_buff_space_limit=
     join->thd->variables.join_buff_space_limit;
+  double partial_join_cardinality=  (join_tab-1)->get_partial_join_cardinality();
   buff= NULL;
   min_buff_size= 0;
   max_buff_size= 0;
   min_records= 1;
-  max_records= join_tab->records;
+  max_records= partial_join_cardinality <= join_buff_space_limit ?
+                 (ulonglong) partial_join_cardinality : join_buff_space_limit;
   set_if_bigger(max_records, 1);
   min_buff_size= get_min_join_buffer_size();
   buff_size= get_max_join_buffer_size();

sql/sql_select.cc

@@ -7720,6 +7720,9 @@ make_join_readinfo(JOIN *join, ulonglong options, uint no_jbuf_after)
       setup_semijoin_dups_elimination(join, options, no_jbuf_after))
     DBUG_RETURN(TRUE); /* purecov: inspected */
 
+  for (i= 0; i < join->const_tables; i++)
+    join->join_tab[i].partial_join_cardinality= 1; 
+
   for (i=join->const_tables ; i < join->tables ; i++)
   {
     JOIN_TAB *tab=join->join_tab+i;
@@ -7731,6 +7734,16 @@ make_join_readinfo(JOIN *join, ulonglong options, uint no_jbuf_after)
     tab->next_select=sub_select;		/* normal select */
     tab->sorted= sorted;
     sorted= 0;                                  // only first must be sorted
+
+    /*
+      The approximation below for partial join cardinality is not good because
+        - it does not take into account some pushdown predicates
+        - it does not differentiate between inner joins, outer joins and semi-joins.
+      Later it should be improved.
+    */
+    tab->partial_join_cardinality= join->best_positions[i].records_read *
+                                   (i ? (tab-1)->partial_join_cardinality : 1);
+ 
     if (tab->loosescan_match_tab)
     {
       if (!(tab->loosescan_buf= (uchar*)join->thd->alloc(tab->

sql/sql_select.h

@@ -217,6 +217,8 @@ typedef struct st_join_table {
   */
   ha_rows       read_time;
     
+  double        partial_join_cardinality;
+
   table_map	dependent,key_dependent;
   uint		use_quick,index;
   uint		status;				///< Save status for cache
@@ -386,6 +388,7 @@ typedef struct st_join_table {
       calc_used_field_length(TRUE);
     return max_used_fieldlength;
   }
+  double get_partial_join_cardinality() { return partial_join_cardinality; }
 } JOIN_TAB;