Index: qc/sql/sql_cache.cc
===================================================================
--- qc.orig/sql/sql_cache.cc
+++ qc/sql/sql_cache.cc
@@ -1322,6 +1322,27 @@ uchar *query_cache_query_get_key(const u
   Functions to store things into the query cache
 *****************************************************************************/
 
+bool Query_cache::is_disabled_ext(void)
+{
+  /* disabled -> enabled */
+  if (is_trace_disabled() && global_system_variables.query_cache_type !=0)
+  {
+    query_cache.update_query_cache_trace(true); 
+    return false;
+  }
+
+  /* enable -> disable */
+  if (!is_trace_disabled() && global_system_variables.query_cache_type ==0)
+  {
+    query_cache.update_query_cache_trace(false); 
+    query_cache.flush();
+    return true;
+  }
+
+  return is_trace_disabled();
+}
+
+
 /*
   Note on double-check locking (DCL) usage.
 
@@ -1388,7 +1409,7 @@ Query_cache::insert(Query_cache_tls *que
   DBUG_ENTER("Query_cache::insert");
 
   /* See the comment on double-check locking usage above. */
-  if (is_disabled() || query_cache_tls->first_query_block == NULL)
+  if (is_disabled_ext() || query_cache_tls->first_query_block == NULL)
     DBUG_VOID_RETURN;
 
   QC_DEBUG_SYNC("wait_in_query_cache_insert");
@@ -1448,7 +1469,7 @@ Query_cache::abort(Query_cache_tls *quer
   THD *thd= current_thd;
 
   /* See the comment on double-check locking usage above. */
-  if (is_disabled() || query_cache_tls->first_query_block == NULL)
+  if (is_disabled_ext() || query_cache_tls->first_query_block == NULL)
     DBUG_VOID_RETURN;
 
   if (try_lock())
@@ -1586,6 +1607,7 @@ Query_cache::Query_cache(ulong query_cac
    query_cache_limit(query_cache_limit_arg),
    queries_in_cache(0), hits(0), inserts(0), refused(0),
    total_blocks(0), lowmem_prunes(0), m_query_cache_is_disabled(FALSE),
+   m_query_cache_trace(false),
    min_allocation_unit(ALIGN_SIZE(min_allocation_unit_arg)),
    min_result_data_size(ALIGN_SIZE(min_result_data_size_arg)),
    def_query_hash_size(ALIGN_SIZE(def_query_hash_size_arg)),
@@ -1962,7 +1984,7 @@ Query_cache::send_result_to_client(THD *
 
     See also a note on double-check locking usage above.
   */
-  if (is_disabled() || thd->locked_tables_mode ||
+  if (is_disabled_ext() || thd->locked_tables_mode ||
       thd->variables.query_cache_type == 0 || query_cache_size == 0)
     goto err;
 
@@ -2304,7 +2326,7 @@ void Query_cache::invalidate(THD *thd, T
 			     my_bool using_transactions)
 {
   DBUG_ENTER("Query_cache::invalidate (table list)");
-  if (is_disabled())
+  if (is_disabled_ext())
     DBUG_VOID_RETURN;
 
   using_transactions= using_transactions && thd->in_multi_stmt_transaction_mode();
@@ -2334,7 +2356,7 @@ void Query_cache::invalidate(THD *thd, T
 void Query_cache::invalidate(CHANGED_TABLE_LIST *tables_used)
 {
   DBUG_ENTER("Query_cache::invalidate (changed table list)");
-  if (is_disabled())
+  if (is_disabled_ext())
     DBUG_VOID_RETURN;
 
   THD *thd= current_thd;
@@ -2363,7 +2385,7 @@ void Query_cache::invalidate(CHANGED_TAB
 void Query_cache::invalidate_locked_for_write(TABLE_LIST *tables_used)
 {
   DBUG_ENTER("Query_cache::invalidate_locked_for_write");
-  if (is_disabled())
+  if (is_disabled_ext())
     DBUG_VOID_RETURN;
 
   THD *thd= current_thd;
@@ -2387,7 +2409,7 @@ void Query_cache::invalidate(THD *thd, T
 			     my_bool using_transactions)
 {
   DBUG_ENTER("Query_cache::invalidate (table)");
-  if (is_disabled())
+  if (is_disabled_ext())
     DBUG_VOID_RETURN;
 
   using_transactions= using_transactions && thd->in_multi_stmt_transaction_mode();
@@ -2405,7 +2427,7 @@ void Query_cache::invalidate(THD *thd, c
 			     my_bool using_transactions)
 {
   DBUG_ENTER("Query_cache::invalidate (key)");
-  if (is_disabled())
+  if (is_disabled_ext())
    DBUG_VOID_RETURN;
 
   using_transactions= using_transactions && thd->in_multi_stmt_transaction_mode();
@@ -2426,7 +2448,7 @@ void Query_cache::invalidate(char *db)
 {
   
   DBUG_ENTER("Query_cache::invalidate (db)");
-  if (is_disabled())
+  if (is_disabled_ext())
     DBUG_VOID_RETURN;
 
   bool restart= FALSE;
@@ -2514,7 +2536,7 @@ void Query_cache::invalidate_by_MyISAM_f
 void Query_cache::flush()
 {
   DBUG_ENTER("Query_cache::flush");
-  if (is_disabled())
+  if (is_disabled_ext())
     DBUG_VOID_RETURN;
 
   QC_DEBUG_SYNC("wait_in_query_cache_flush1");
@@ -2547,7 +2569,7 @@ void Query_cache::pack(ulong join_limit,
 {
   DBUG_ENTER("Query_cache::pack");
 
-  if (is_disabled())
+  if (is_disabled_ext())
     DBUG_VOID_RETURN;
 
   /*
@@ -2616,7 +2638,10 @@ void Query_cache::init()
     be used.
   */
   if (global_system_variables.query_cache_type == 0)
+  {
     query_cache.disable_query_cache();
+    query_cache.update_query_cache_trace(false);
+  }
 
   DBUG_VOID_RETURN;
 }
Index: qc/sql/sql_cache.h
===================================================================
--- qc.orig/sql/sql_cache.h
+++ qc/sql/sql_cache.h
@@ -297,10 +297,12 @@ private:
   Cache_lock_status m_cache_lock_status;
 
   bool m_query_cache_is_disabled;
+  bool volatile m_query_cache_trace;
 
   void free_query_internal(Query_cache_block *point);
   void invalidate_table_internal(THD *thd, uchar *key, uint32 key_length);
   void disable_query_cache(void) { m_query_cache_is_disabled= TRUE; }
+  void update_query_cache_trace(bool new_flag) { m_query_cache_trace = new_flag; }
 
 protected:
   /*
@@ -445,7 +447,10 @@ protected:
 	      uint def_table_hash_size = QUERY_CACHE_DEF_TABLE_HASH_SIZE);
 
   bool is_disabled(void) { return m_query_cache_is_disabled; }
-
+  bool is_trace_disabled(void) { return !m_query_cache_trace; }
+  
+  /* extensional implementation of is_disabled */
+  bool is_disabled_ext(void);
   /* initialize cache (mutex) */
   void init();
   /* resize query cache (return real query size, 0 if disabled) */
Index: qc/sql/sys_vars.cc
===================================================================
--- qc.orig/sql/sys_vars.cc
+++ qc/sql/sys_vars.cc
@@ -1866,7 +1866,7 @@ static Sys_var_ulong Sys_query_cache_min
 static const char *query_cache_type_names[]= { "OFF", "ON", "DEMAND", 0 };
 static bool check_query_cache_type(sys_var *self, THD *thd, set_var *var)
 {
-  if (query_cache.is_disabled())
+  if (query_cache.is_disabled_ext())
   {
     my_error(ER_QUERY_CACHE_DISABLED, MYF(0));
     return true;
@@ -1879,8 +1879,8 @@ static Sys_var_enum Sys_query_cache_type
        "except SELECT SQL_NO_CACHE ... queries. DEMAND = Cache only "
        "SELECT SQL_CACHE ... queries",
        SESSION_VAR(query_cache_type), CMD_LINE(REQUIRED_ARG),
-       query_cache_type_names, DEFAULT(1), NO_MUTEX_GUARD, NOT_IN_BINLOG,
-       ON_CHECK(check_query_cache_type));
+       query_cache_type_names, DEFAULT(1), NO_MUTEX_GUARD, NOT_IN_BINLOG/*,
+       ON_CHECK(check_query_cache_type)*/);
 
 static Sys_var_mybool Sys_query_cache_wlock_invalidate(
        "query_cache_wlock_invalidate",