support of concurent query cache resizing (BUG#12848)

sql/mysql_priv.h

@@ -318,6 +318,7 @@ inline THD *_current_thd(void)
 #define query_cache_store_query(A, B) query_cache.store_query(A, B)
 #define query_cache_destroy() query_cache.destroy()
 #define query_cache_result_size_limit(A) query_cache.result_size_limit(A)
+#define query_cache_init() query_cache.init()
 #define query_cache_resize(A) query_cache.resize(A)
 #define query_cache_invalidate3(A, B, C) query_cache.invalidate(A, B, C)
 #define query_cache_invalidate1(A) query_cache.invalidate(A)
@@ -329,6 +330,7 @@ inline THD *_current_thd(void)
 #define query_cache_store_query(A, B)
 #define query_cache_destroy()
 #define query_cache_result_size_limit(A)
+#define query_cache_init()
 #define query_cache_resize(A)
 #define query_cache_invalidate3(A, B, C)
 #define query_cache_invalidate1(A)

sql/mysqld.cc

@@ -2461,6 +2461,7 @@ You should consider changing lower_case_table_names to 1 or 2",
     unireg_abort(1);
   }
   query_cache_result_size_limit(query_cache_limit);
+  query_cache_init();
   query_cache_resize(query_cache_size);
   randominit(&sql_rand,(ulong) start_time,(ulong) start_time/2);
   reset_floating_point_exceptions();

sql/sql_cache.cc

@@ -563,13 +563,18 @@ void query_cache_insert(NET *net, const char *packet, ulong length)
 {
   DBUG_ENTER("query_cache_insert");
 
-#ifndef DBUG_OFF
-  // Check if we have called query_cache.wreck() (which disables the cache)
-  if (query_cache.query_cache_size == 0)
+  STRUCT_LOCK(&query_cache.structure_guard_mutex);
+  /*
+    It is very unlikely that following condition is TRUE (it is possible
+    only if other thread is resizing cache), so we check it only after guard
+    mutex lock
+  */
+  if (unlikely(query_cache.query_cache_size == 0))
+  {
+    STRUCT_UNLOCK(&query_cache.structure_guard_mutex);
     DBUG_VOID_RETURN;
-#endif
+  }
 
-  STRUCT_LOCK(&query_cache.structure_guard_mutex);
   Query_cache_block *query_block = ((Query_cache_block*)
 				    net->query_cache_query);
   if (query_block)
@@ -612,14 +617,20 @@ void query_cache_abort(NET *net)
 {
   DBUG_ENTER("query_cache_abort");
 
-#ifndef DBUG_OFF
-  // Check if we have called query_cache.wreck() (which disables the cache)
-  if (query_cache.query_cache_size == 0)
-    DBUG_VOID_RETURN;
-#endif
   if (net->query_cache_query != 0)	// Quick check on unlocked structure
   {
     STRUCT_LOCK(&query_cache.structure_guard_mutex);
+    /*
+      It is very unlikely that following condition is TRUE (it is possible
+      only if other thread is resizing cache), so we check it only after guard
+      mutex lock
+    */
+    if (unlikely(query_cache.query_cache_size == 0))
+    {
+      STRUCT_UNLOCK(&query_cache.structure_guard_mutex);
+      DBUG_VOID_RETURN;
+    }
+
     Query_cache_block *query_block = ((Query_cache_block*)
 				       net->query_cache_query);
     if (query_block)			// Test if changed by other thread
@@ -641,14 +652,20 @@ void query_cache_end_of_result(NET *net)
 {
   DBUG_ENTER("query_cache_end_of_result");
 
-#ifndef DBUG_OFF
-  // Check if we have called query_cache.wreck() (which disables the cache)
-  if (query_cache.query_cache_size == 0) DBUG_VOID_RETURN;
-#endif
-
   if (net->query_cache_query != 0)	// Quick check on unlocked structure
   {
     STRUCT_LOCK(&query_cache.structure_guard_mutex);
+    /*
+      It is very unlikely that following condition is TRUE (it is possible
+      only if other thread is resizing cache), so we check it only after guard
+      mutex lock
+    */
+    if (unlikely(query_cache.query_cache_size == 0))
+    {
+      STRUCT_UNLOCK(&query_cache.structure_guard_mutex);
+      DBUG_VOID_RETURN;
+    }
+
     Query_cache_block *query_block = ((Query_cache_block*)
 				      net->query_cache_query);
     if (query_block)
@@ -728,9 +745,14 @@ ulong Query_cache::resize(ulong query_cache_size_arg)
   DBUG_ENTER("Query_cache::resize");
   DBUG_PRINT("qcache", ("from %lu to %lu",query_cache_size,
 			query_cache_size_arg));
-  free_cache(0);
+  DBUG_ASSERT(initialized);
+  STRUCT_LOCK(&structure_guard_mutex);
+  if (query_cache_size > 0)
+    free_cache();
   query_cache_size= query_cache_size_arg;
-  DBUG_RETURN(::query_cache_size= init_cache());
+  ::query_cache_size= init_cache();
+  STRUCT_UNLOCK(&structure_guard_mutex);
+  DBUG_RETURN(::query_cache_size);
 }
 
 
@@ -1307,7 +1329,7 @@ void Query_cache::destroy()
   }
   else
   {
-    free_cache(1);
+    free_cache();
     pthread_mutex_destroy(&structure_guard_mutex);
     initialized = 0;
   }
@@ -1336,8 +1358,6 @@ ulong Query_cache::init_cache()
   int align;
 
   DBUG_ENTER("Query_cache::init_cache");
-  if (!initialized)
-    init();
   approx_additional_data_size = (sizeof(Query_cache) +
 				 sizeof(gptr)*(def_query_hash_size+
 					       def_table_hash_size));
@@ -1395,14 +1415,9 @@ ulong Query_cache::init_cache()
     goto err;
   query_cache_size -= additional_data_size;
 
-  STRUCT_LOCK(&structure_guard_mutex);
-
-  if (!(cache = (byte *)
-	 my_malloc_lock(query_cache_size+additional_data_size, MYF(0))))
-  {
-    STRUCT_UNLOCK(&structure_guard_mutex);
+  if (!(cache= (byte *)
+        my_malloc_lock(query_cache_size+additional_data_size, MYF(0))))
     goto err;
-  }
 
   DBUG_PRINT("qcache", ("cache length %lu, min unit %lu, %u bins",
 		      query_cache_size, min_allocation_unit, mem_bin_num));
@@ -1482,7 +1497,6 @@ ulong Query_cache::init_cache()
 
   queries_in_cache = 0;
   queries_blocks = 0;
-  STRUCT_UNLOCK(&structure_guard_mutex);
   DBUG_RETURN(query_cache_size +
 	      additional_data_size + approx_additional_data_size);
 
@@ -1498,6 +1512,7 @@ void Query_cache::make_disabled()
 {
   DBUG_ENTER("Query_cache::make_disabled");
   query_cache_size= 0;
+  queries_blocks= 0;
   free_memory= 0;
   bins= 0;
   steps= 0;
@@ -1509,14 +1524,11 @@ void Query_cache::make_disabled()
 }
 
 
-void Query_cache::free_cache(my_bool destruction)
+void Query_cache::free_cache()
 {
   DBUG_ENTER("Query_cache::free_cache");
   if (query_cache_size > 0)
   {
-    if (!destruction)
-      STRUCT_LOCK(&structure_guard_mutex);
-
     flush_cache();
 #ifndef DBUG_OFF
     if (bins[0].free_blocks == 0)
@@ -1538,8 +1550,6 @@ void Query_cache::free_cache(my_bool destruction)
     make_disabled();
     hash_free(&queries);
     hash_free(&tables);
-    if (!destruction)
-      STRUCT_UNLOCK(&structure_guard_mutex);
   }
   DBUG_VOID_RETURN;
 }
@@ -2149,7 +2159,19 @@ Query_cache::allocate_block(ulong len, my_bool not_less, ulong min,
   }
 
   if (!under_guard)
+  {
     STRUCT_LOCK(&structure_guard_mutex);
+    /*
+      It is very unlikely that following condition is TRUE (it is possible
+      only if other thread is resizing cache), so we check it only after
+      guard mutex lock
+    */
+    if (unlikely(query_cache.query_cache_size == 0))
+    {
+      STRUCT_UNLOCK(&structure_guard_mutex);
+      DBUG_RETURN(0);
+    }
+  }
 
   /* Free old queries until we have enough memory to store this block */
   Query_cache_block *block;
@@ -2606,6 +2628,17 @@ void Query_cache::pack_cache()
 {
   DBUG_ENTER("Query_cache::pack_cache");
   STRUCT_LOCK(&structure_guard_mutex);
+  /*
+    It is very unlikely that following condition is TRUE (it is possible
+    only if other thread is resizing cache), so we check it only after
+    guard mutex lock
+  */
+  if (unlikely(query_cache_size == 0))
+  {
+    STRUCT_UNLOCK(&structure_guard_mutex);
+    DBUG_VOID_RETURN;
+  }
+
   DBUG_EXECUTE("check_querycache",query_cache.check_integrity(1););
 
   byte *border = 0;
@@ -2915,6 +2948,7 @@ my_bool Query_cache::join_results(ulong join_limit)
   STRUCT_LOCK(&structure_guard_mutex);
   if (queries_blocks != 0)
   {
+    DBUG_ASSERT(query_cache_size > 0);
     Query_cache_block *block = queries_blocks;
     do
     {
@@ -3209,7 +3243,19 @@ my_bool Query_cache::check_integrity(bool not_locked)
     DBUG_RETURN(0);
   }
   if (!not_locked)
+  {
     STRUCT_LOCK(&structure_guard_mutex);
+    /*
+      It is very unlikely that following condition is TRUE (it is possible
+      only if other thread is resizing cache), so we check it only after
+      guard mutex lock
+    */
+    if (unlikely(query_cache_size == 0))
+    {
+      STRUCT_UNLOCK(&query_cache.structure_guard_mutex);
+      DBUG_RETURN(0);
+    }
+  }
 
   if (hash_check(&queries))
   {

sql/sql_cache.h

@@ -310,10 +310,9 @@ protected:
     Following function control structure_guard_mutex
     by themself or don't need structure_guard_mutex
   */
-  void init();
   ulong init_cache();
   void make_disabled();
-  void free_cache(my_bool destruction);
+  void free_cache();
   Query_cache_block *write_block_data(ulong data_len, gptr data,
 				       ulong header_len,
 				       Query_cache_block::block_type type,
@@ -346,6 +345,8 @@ protected:
 	      uint def_query_hash_size = QUERY_CACHE_DEF_QUERY_HASH_SIZE,
 	      uint def_table_hash_size = QUERY_CACHE_DEF_TABLE_HASH_SIZE);
 
+  /* initialize cache (mutex) */
+  void init();
   /* resize query cache (return real query size, 0 if disabled) */
   ulong resize(ulong query_cache_size);
   inline void result_size_limit(ulong limit){query_cache_limit=limit;}