Fixed bug #21727.

This is a performance issue for queries with subqueries evaluation
of which requires filesort.
Allocation of memory for the sort buffer at each evaluation of a
subquery may take a significant amount of time if the buffer is rather big.
With the fix we allocate the buffer at the first evaluation of the
subquery and reuse it at each subsequent evaluation.


mysql-test/r/subselect.result:
  Added a test case for bug #21727.
mysql-test/t/subselect.test:
  Added a test case for bug #21727.
sql/item_subselect.h:
  Fixed bug #21727.
  This is a performance issue for queries with subqueries evaluation
  of which requires filesort.
  Added an implementation for Item_subselect::is_uncacheable()
  returning TRUE if the engine if the subselect is uncacheable.
sql/mysql_priv.h:
  Fixed bug #21727.
  This is a performance issue for queries with subqueries evaluation
  of which requires filesort.
  Added a new boolean parameter to the filesort_free_buffers procedure.
  If the value of this parameter is TRUE the procedure frees the sort_keys
  buffpek buffers.
sql/records.cc:
  Fixed bug #21727.
  This is a performance issue for queries with subqueries evaluation
  of which requires filesort.
  Added a new boolean parameter to the filesort_free_buffers procedure.
  If the value of this parameter is TRUE the procedure frees the sort_keys
  buffpek buffers.
sql/sql_base.cc:
  Fixed bug #21727.
  Made sure that st_table::pos_in_table_list would be always initialized.
sql/sql_select.cc:
  Fixed bug #21727.
  This is a performance issue for queries with subqueries evaluation
  of which requires filesort.
  Added a new boolean parameter to the filesort_free_buffers procedure.
  If the value of this parameter is TRUE the procedure frees the sort_keys
  buffpek buffers.
sql/sql_show.cc:
  Fixed bug #21727.
  This is a performance issue for queries with subqueries evaluation
  of which requires filesort.
  Added a new boolean parameter to the filesort_free_buffers procedure.
  If the value of this parameter is TRUE the procedure frees the sort_keys
  buffpek buffers.
sql/sql_table.cc:
  Fixed bug #21727.
  This is a performance issue for queries with subqueries evaluation
  of which requires filesort.
  Cleanup.
sql/table.cc:
  Fixed bug #21727.
  This is a performance issue for queries with subqueries evaluation
  of which requires filesort.
  Added st_table_list::in_subselect() returning for a table the subselect that 
  contains the FROM list this table is taken from (if there is any).
sql/table.h:
  Fixed bug #21727.
  This is a performance issue for queries with subqueries evaluation
  of which requires filesort.
  Added fields for sort_keys and buffpek buffers to the FILESORT_INFO structure.

1 files changed, 37 insertions, 0 deletions

diff --git a/mysql-test/t/subselect.test b/mysql-test/t/subselect.test
index 6d5082c360b..2f3ae3347e8 100644
--- a/mysql-test/t/subselect.test
+++ b/mysql-test/t/subselect.test
@@ -2426,3 +2426,40 @@ SELECT (
 FROM t1 t2
 GROUP BY t2.a;
 DROP TABLE t1,t2;  
+
+#
+# Bug #21727: Correlated subquery that requires filesort:
+#             slow with big sort_buffer_size 
+#
+
+CREATE TABLE t1 (a int, b int auto_increment, PRIMARY KEY (b));
+CREATE TABLE t2 (x int auto_increment, y int, z int,
+                 PRIMARY KEY (x), FOREIGN KEY (y) REFERENCES t1 (b));
+
+disable_query_log;
+let $1=3000;
+while ($1)
+{
+  eval INSERT INTO t1(a) VALUES(RAND()*1000);
+  eval SELECT MAX(b) FROM t1 INTO @id;
+  let $2=10;
+  while ($2)
+  {
+    eval INSERT INTO t2(y,z) VALUES(@id,RAND()*1000);
+    dec $2;
+  } 
+  dec $1;
+}
+enable_query_log;
+
+SET SESSION sort_buffer_size = 32 * 1024;
+SELECT SQL_NO_CACHE COUNT(*) 
+  FROM (SELECT  a, b, (SELECT x FROM t2 WHERE y=b ORDER BY z DESC LIMIT 1) c
+          FROM t1) t;
+
+SET SESSION sort_buffer_size = 8 * 1024 * 1024;
+SELECT SQL_NO_CACHE COUNT(*) 
+  FROM (SELECT  a, b, (SELECT x FROM t2 WHERE y=b ORDER BY z DESC LIMIT 1) c
+          FROM t1) t;
+
+DROP TABLE t1,t2;