Bug#21074 Large query_cache freezes mysql server sporadically under heavy load

Invaldating a subset of a sufficiently large query cache can take a long time.
During this time the server is efficiently frozen and no other operation can
be executed. This patch addresses this problem by moving the locks which cause
the freezing and also by temporarily disable the query cache while the 
invalidation takes place.

1 files changed, 12 insertions, 4 deletions

diff --git a/sql/sql_rename.cc b/sql/sql_rename.cc
index f34ec83b29c..b87c74dc179 100644
--- a/sql/sql_rename.cc
+++ b/sql/sql_rename.cc
@@ -144,10 +144,14 @@ bool mysql_rename_tables(THD *thd, TABLE_LIST *table_list, bool silent)
     }
   }
 
-  VOID(pthread_mutex_lock(&LOCK_open));
-  if (lock_table_names(thd, table_list))
+  pthread_mutex_lock(&LOCK_open);
+  if (lock_table_names_exclusively(thd, table_list))
+  {
+    pthread_mutex_unlock(&LOCK_open);
     goto err;
-  
+  }
+  pthread_mutex_unlock(&LOCK_open);
+
   error=0;
   if ((ren_table=rename_tables(thd,table_list,0)))
   {
@@ -183,10 +187,14 @@ bool mysql_rename_tables(THD *thd, TABLE_LIST *table_list, bool silent)
     send_ok(thd);
   }
 
+  if (!error)
+    query_cache_invalidate3(thd, table_list, 0);
+
+  pthread_mutex_lock(&LOCK_open);
   unlock_table_names(thd, table_list, (TABLE_LIST*) 0);
+  pthread_mutex_unlock(&LOCK_open);
 
 err:
-  pthread_mutex_unlock(&LOCK_open);
   /* enable logging back if needed */
   if (disable_logs)
   {