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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.

mysql-test/r/query_cache_debug.result:
  Add test case result for Bug#41098
mysql-test/t/disabled.def:
  Re-enable test case.
mysql-test/t/query_cache_debug.test:
  Add test case for Bug#41098
sql/sql_cache.cc:
  Debug sync point for regression testing purposes.
sql/sql_insert.cc:
  Remove meaningless query cache invalidate. There is already
  a preceding invalidate for queries that started before the
  concurrent insert.
storage/myisam/ha_myisam.cc:
  Check for a active concurrent insert.
storage/myisam/mi_locking.c:
  Signal the start of a concurrent insert. Flag is zeroed once
  the state is updated back.
storage/myisam/myisamdef.h:
  Add flag to signal a active concurrent insert.
This commit is contained in:
Davi Arnaut
2009-02-19 18:09:35 -03:00
parent 8e8c5bbe7a
commit 664bb23a30
8 changed files with 132 additions and 15 deletions
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68
mysql-test/t/query_cache_debug.test
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@ -44,3 +44,71 @@ set global query_cache_size= 0;
use test;
drop table t1;
#
# Bug#41098: Query Cache returns wrong result with concurrent insert
#
SET @old_concurrent_insert= @@GLOBAL.concurrent_insert;
SET @old_query_cache_size= @@GLOBAL.query_cache_size;
--disable_warnings
DROP TABLE IF EXISTS t1, t2;
--enable_warnings
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;
connect(con1,localhost,root,,test,,);
connect(con2,localhost,root,,test,,);
connection con1;
--echo # Switch to connection con1
SET SESSION debug='+d,wait_after_query_cache_invalidate';
--echo # Send concurrent insert, will wait in the query cache table invalidate
--send INSERT INTO t1 VALUES (4)
connection default;
--echo # Switch to connection default
--echo # Wait for concurrent insert to reach the debug point
let $wait_condition=
SELECT COUNT(*) = 1 FROM INFORMATION_SCHEMA.PROCESSLIST
WHERE STATE = "wait_after_query_cache_invalidate" AND
INFO = "INSERT INTO t1 VALUES (4)";
--source include/wait_condition.inc
connection con2;
--echo # Switch to connection con2
--echo # Send SELECT that shouldn't be cached
SELECT * FROM t1;
connection default;
--echo # Switch to connection default
--echo # 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;
connection con1;
--echo # Switch to connection con1
--echo # Gather insert result
--reap
SHOW STATUS LIKE "Qcache_queries_in_cache";
--echo # Test that it's cacheable
SELECT * FROM t1;
SHOW STATUS LIKE "Qcache_queries_in_cache";
--echo # Disconnect
disconnect con1;
disconnect con2;
connection default;
--echo # 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;