Bug #30887 Server crashes on SET GLOBAL query_cache_size=0
Submitted: 7 Sep 2007 8:29 Modified: 25 Jan 2008 19:32
Reporter: Kristofer Pettersson Email Updates:
Status: Closed Impact on me:
None 
Category:MySQL Server: Query Cache Severity:S2 (Serious)
Version:5.1 BK OS:Any
Assigned to: Kristofer Pettersson CPU Architecture:Any

[7 Sep 2007 8:29] Kristofer Pettersson 
Description:
Reseting the query cache by issuing a SET GLOBAL query_cache_size=0 will cause the server to crash if a the server concurrently is saving a new result set to the query cache. The reason for this is that the fast invalidation isn't waiting on the result writers to release the block level locks in the query cache.

How to repeat:
* INSERT a set of fairly large blobs into a table as (nr,blobl)
* Activate query cache and start SELECTing.
* Concurrently change query cache size between 0 and 100000 until the server crash.

Suggested fix:
Count result writers and don't free the cache unless there are no active result writers.
[7 Dec 2007 10:28] Bugs System 
A patch for this bug has been committed. After review, it may
be pushed to the relevant source trees for release in the next
version. You can access the patch from:

  http://lists.mysql.com/commits/39505

ChangeSet@1.2649, 2007-12-07 11:31:55+01:00, thek@adventure.(none) +3 -0
  Bug#30887 Server crashes on SET GLOBAL query_cache_size=0
  
  Reseting the query cache by issuing a SET GLOBAL query_cache_size=0 caused the server
  to crash if a the server concurrently was saving a new result set to the query cache. The
  reason for this was that the invalidation wasn't waiting on the result writers to
  release the block level locks on the query cache.
[3 Jan 2008 14:32] Bugs System 
A patch for this bug has been committed. After review, it may
be pushed to the relevant source trees for release in the next
version. You can access the patch from:

  http://lists.mysql.com/commits/40509

ChangeSet@1.2649, 2008-01-03 15:36:48+01:00, thek@adventure.(none) +3 -0
  Bug#30887 Server crashes on SET GLOBAL query_cache_size=0
  
  Reseting the query cache by issuing a SET GLOBAL query_cache_size=0 caused the server
  to crash if a the server concurrently was saving a new result set to the query cache. The
  reason for this was that the invalidation wasn't waiting on the result writers to
  release the block level locks on the query cache.
[25 Jan 2008 12:35] Bugs System 
Pushed into 5.1.24-rc
[25 Jan 2008 12:38] Bugs System 
Pushed into 6.0.5-alpha
[25 Jan 2008 19:32] Paul DuBois 
Noted in 5.1.24, 6.0.5 changelogs.
[8 Feb 2008 6:41] MySQL Verification Team 
FYI, the stack trace in a possible crash looks like this:

mysqld-debug.exe!Query_cache_query::result
mysqld-debug.exe!query_cache_insert
mysqld-debug.exe!net_real_write
mysqld-debug.exe!net_flush
mysqld-debug.exe!net_send_eof
mysqld-debug.exe!net_end_statement
mysqld-debug.exe!dispatch_command
mysqld-debug.exe!do_command
mysqld-debug.exe!handle_one_connection
mysqld-debug.exe!pthread_start
mysqld-debug.exe!_callthreadstart
mysqld-debug.exe!_threadstart
kernel32.dll!BaseThreadStart()  + 0x3a bytes
[6 Mar 2008 9:38] Jon Stephens 
Also documented for 5.1.23-ndb-6.2.14.
[30 Mar 2008 19:43] Jon Stephens 
Also documented for 5.1.23-ndb-6.3.11.