MDEV-5011: ERROR Plugin 'MEMORY' has ref_count=1 after shutdown for SJM queries

- Provide a special execution path for cleanup of degenerate 
  non-merged semi-join children of degenerate selects.

mysql-test/r/subselect_mat.result

@@ -2015,6 +2015,14 @@ SELECT * FROM t1 WHERE 8 IN ( SELECT MIN(pk) FROM t1 ) AND ( pk = a OR pk = b );
 pk	a	b
 drop table t1;
 SET optimizer_switch=@save_optimizer_switch;
+#
+# MDEV-5011: ERROR Plugin 'MEMORY' has ref_count=1 after shutdown for SJM queries
+#
+CREATE TABLE t1 (pk INT, a INT, b INT, PRIMARY KEY(pk)) ENGINE=MyISAM;
+INSERT INTO t1 VALUES (1,3,5),(2,4,6);
+SELECT * FROM t1 WHERE 8 IN (SELECT MIN(pk) FROM t1) AND (pk = a OR pk = b);
+pk	a	b
+DROP TABLE t1;
 # End of 5.3 tests
 set @subselect_mat_test_optimizer_switch_value=null;
 set @@optimizer_switch='materialization=on,in_to_exists=off,semijoin=off';

mysql-test/r/subselect_sj_mat.result

@@ -2055,4 +2055,12 @@ SELECT * FROM t1 WHERE 8 IN ( SELECT MIN(pk) FROM t1 ) AND ( pk = a OR pk = b );
 pk	a	b
 drop table t1;
 SET optimizer_switch=@save_optimizer_switch;
+#
+# MDEV-5011: ERROR Plugin 'MEMORY' has ref_count=1 after shutdown for SJM queries
+#
+CREATE TABLE t1 (pk INT, a INT, b INT, PRIMARY KEY(pk)) ENGINE=MyISAM;
+INSERT INTO t1 VALUES (1,3,5),(2,4,6);
+SELECT * FROM t1 WHERE 8 IN (SELECT MIN(pk) FROM t1) AND (pk = a OR pk = b);
+pk	a	b
+DROP TABLE t1;
 # End of 5.3 tests

mysql-test/t/subselect_sj_mat.test

@@ -1698,4 +1698,12 @@ SELECT * FROM t1 WHERE 8 IN ( SELECT MIN(pk) FROM t1 ) AND ( pk = a OR pk = b );
 drop table t1;
 SET optimizer_switch=@save_optimizer_switch;
 
+--echo #
+--echo # MDEV-5011: ERROR Plugin 'MEMORY' has ref_count=1 after shutdown for SJM queries
+--echo #
+CREATE TABLE t1 (pk INT, a INT, b INT, PRIMARY KEY(pk)) ENGINE=MyISAM;
+INSERT INTO t1 VALUES (1,3,5),(2,4,6);
+SELECT * FROM t1 WHERE 8 IN (SELECT MIN(pk) FROM t1) AND (pk = a OR pk = b);
+DROP TABLE t1;
+
 --echo # End of 5.3 tests

sql/opt_subselect.cc

@@ -5174,6 +5174,12 @@ bool setup_jtbm_semi_joins(JOIN *join, List<TABLE_LIST> *join_list,
           DBUG_RETURN(1);
         table->table= dummy_table;
         table->table->pos_in_table_list= table;
+        /*
+          Note: the table created above may be freed by:
+          1. JOIN_TAB::cleanup(), when the parent join is a regular join.
+          2. cleanup_empty_jtbm_semi_joins(), when the parent join is a
+             degenerate join (e.g. one with "Impossible where").
+        */
         setup_table_map(table->table, table, table->jtbm_table_no);
       }
       else
@@ -5206,6 +5212,42 @@ bool setup_jtbm_semi_joins(JOIN *join, List<TABLE_LIST> *join_list,
 }
 
 
+/*
+  Cleanup non-merged semi-joins (JBMs) that have empty.
+
+  This function is to cleanups for a special case:  
+  Consider a query like 
+
+    select * from t1 where 1=2 AND t1.col IN (select max(..) ... having 1=2)
+
+  For this query, optimization of subquery will short-circuit, and 
+  setup_jtbm_semi_joins() will call create_dummy_tmp_table() so that we have
+  empty, constant temp.table to stand in as materialized temp. table.
+
+  Now, suppose that the upper join is also found to be degenerate. In that
+  case, no JOIN_TAB array will be produced, and hence, JOIN::cleanup() will
+  have a problem with cleaning up empty JTBMs (non-empty ones are cleaned up
+  through Item::cleanup() calls).
+*/
+
+void cleanup_empty_jtbm_semi_joins(JOIN *join)
+{
+  List_iterator<TABLE_LIST> li(*join->join_list);
+  TABLE_LIST *table;
+  while ((table= li++))
+  {
+    if ((table->jtbm_subselect && table->jtbm_subselect->is_jtbm_const_tab))
+    {
+      if (table->table)
+      {
+        free_tmp_table(join->thd, table->table);
+        table->table= NULL;
+      }
+    }
+  }
+}
+
+
 /**
   Choose an optimal strategy to execute an IN/ALL/ANY subquery predicate
   based on cost.

sql/opt_subselect.h

@@ -12,6 +12,7 @@ int pull_out_semijoin_tables(JOIN *join);
 bool optimize_semijoin_nests(JOIN *join, table_map all_table_map);
 bool setup_jtbm_semi_joins(JOIN *join, List<TABLE_LIST> *join_list,  
                            Item **join_where);
+void cleanup_empty_jtbm_semi_joins(JOIN *join);
 
 // used by Loose_scan_opt
 ulonglong get_bound_sj_equalities(TABLE_LIST *sj_nest, 

sql/sql_select.cc

@@ -10125,6 +10125,11 @@ void JOIN_TAB::cleanup()
     {
       if (table->pos_in_table_list->jtbm_subselect->is_jtbm_const_tab)
       {
+        /*
+          Set this to NULL so that cleanup_empty_jtbm_semi_joins() doesn't
+          attempt to make another free_tmp_table call.
+        */
+        table->pos_in_table_list->table= NULL;
         free_tmp_table(join->thd, table);
         table= NULL;
       }
@@ -10461,6 +10466,7 @@ void JOIN::cleanup(bool full)
   }
   if (full)
   {
+    cleanup_empty_jtbm_semi_joins(this);
     /* 
       Ensure that the following delete_elements() would not be called
       twice for the same list.