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Bug#41098: Query Cache returns wrong result with concurrent insert

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The problem is that select queries executed concurrently with
a concurrent insert on a MyISAM table could be cached if the
select started after the query cache invalidation but before
the unlock of tables performed by the concurrent insert. This
race could happen because the concurrent insert was failing
to prevent cache of select queries happening at the same time.

The solution is to add a 'uncacheable' status flag to signal
that a concurrent insert is being performed on the table and
that queries executing at the same time shouldn't cache the
results.
This commit is contained in:
Davi Arnaut
2009-02-19 18:09:35 -03:00
parent 123549e7e8
commit a2e4449bfc
8 changed files with 132 additions and 15 deletions
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49
mysql-test/r/query_cache_debug.result
View File

@ -22,3 +22,52 @@ Qcache_queries_in_cache 0
set global query_cache_size= 0;
use test;
drop table t1;
SET @old_concurrent_insert= @@GLOBAL.concurrent_insert;
SET @old_query_cache_size= @@GLOBAL.query_cache_size;
DROP TABLE IF EXISTS t1, t2;
CREATE TABLE t1 (a INT);
CREATE TABLE t2 (a INT);
INSERT INTO t1 VALUES (1),(2),(3);
SET GLOBAL concurrent_insert= 1;
SET GLOBAL query_cache_size= 1024*512;
SET GLOBAL query_cache_type= ON;
# Switch to connection con1
SET SESSION debug='+d,wait_after_query_cache_invalidate';
# Send concurrent insert, will wait in the query cache table invalidate
INSERT INTO t1 VALUES (4);
# Switch to connection default
# Wait for concurrent insert to reach the debug point
# Switch to connection con2
# Send SELECT that shouldn't be cached
SELECT * FROM t1;
a
1
2
3
# Switch to connection default
# Notify the concurrent insert to proceed
SELECT ID FROM INFORMATION_SCHEMA.PROCESSLIST
WHERE STATE = 'wait_after_query_cache_invalidate' INTO @thread_id;
KILL QUERY @thread_id;
# Switch to connection con1
# Gather insert result
SHOW STATUS LIKE "Qcache_queries_in_cache";
Variable_name Value
Qcache_queries_in_cache 0
# Test that it's cacheable
SELECT * FROM t1;
a
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2
3
4
SHOW STATUS LIKE "Qcache_queries_in_cache";
Variable_name Value
Qcache_queries_in_cache 1
# Disconnect
# Restore defaults
RESET QUERY CACHE;
DROP TABLE t1,t2;
SET GLOBAL concurrent_insert= DEFAULT;
SET GLOBAL query_cache_size= DEFAULT;
SET GLOBAL query_cache_type= DEFAULT;