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SET @query_cache_type= @@global.query_cache_type; SET @query_cache_limit= @@global.query_cache_limit; SET @query_cache_min_res_unit= @@global.query_cache_min_res_unit; SET @query_cache_size= @@global.query_cache_size; # Bug#28249 Query Cache returns wrong result with concurrent insert/ certain lock # Establish connections user1,user2,user3 (user=root) # Switch to connection user1 SET GLOBAL query_cache_type=1; SET GLOBAL query_cache_limit=10000; SET GLOBAL query_cache_min_res_unit=0; SET GLOBAL query_cache_size= 102400; FLUSH TABLES; DROP TABLE IF EXISTS t1, t2; CREATE TABLE t1 (a INT); CREATE TABLE t2 (a INT); INSERT INTO t1 VALUES (1),(2),(3); # Switch to connection user2 LOCK TABLE t2 WRITE; # Switch to connection user1 # "send" the next select, "reap" the result later. # The select will be blocked by the write lock on the t1. SELECT *, (SELECT COUNT(*) FROM t2) FROM t1; # Switch to connection user3 # Poll till the select of connection user1 is blocked by the write lock on t1. SELECT user,command,state,info FROM information_schema.processlist WHERE state = 'Waiting for table metadata lock' AND info = 'SELECT *, (SELECT COUNT(*) FROM t2) FROM t1'; user command state info root Query Waiting for table metadata lock SELECT *, (SELECT COUNT(*) FROM t2) FROM t1 INSERT INTO t1 VALUES (4); # Switch to connection user2 UNLOCK TABLES; # Switch to connection user1 # Collecting ("reap") the result from the previously blocked select. # The printing of the result (varies between 3 and 4 rows) set has to be suppressed. # Switch to connection user3 # The next select enforces that effects of "concurrent_inserts" like the # record with a = 4 is missing in result sets can no more happen. SELECT 1 FROM t1 WHERE a = 4; 1 1 # Switch to connection user1 # The next result set must contain 4 rows. SELECT *, (SELECT COUNT(*) FROM t2) FROM t1; a (SELECT COUNT(*) FROM t2) 1 0 2 0 3 0 4 0 RESET QUERY CACHE; SELECT *, (SELECT COUNT(*) FROM t2) FROM t1; a (SELECT COUNT(*) FROM t2) 1 0 2 0 3 0 4 0 DROP TABLE t1,t2; # Switch to connection default + close connections user1,user2,user3 SET GLOBAL query_cache_type= @query_cache_type; SET GLOBAL query_cache_limit= @query_cache_limit; SET GLOBAL query_cache_min_res_unit= @query_cache_min_res_unit; SET GLOBAL query_cache_size= @query_cache_size;