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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= 100000;
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 = 'Locked'
AND info = 'SELECT *, (SELECT COUNT(*) FROM t2) FROM t1';
user command state info
root Query Locked 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;
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