[hibernate-issues] [Hibernate-JIRA] Created: (HHH-4550) query cache: Attention with configuring Update Timestamps Cache region: expired entries cause wrong result sets!

[Guenther Demetz (JIRA)]

query cache: Attention with configuring Update Timestamps Cache region: expired entries cause wrong result sets!
----------------------------------------------------------------------------------------------------------------

                 Key: HHH-4550
                 URL: http://opensource.atlassian.com/projects/hibernate/browse/HHH-4550
             Project: Hibernate Core
          Issue Type: Improvement
          Components: caching (L2)
    Affects Versions: 3.3.2
         Environment: 3.3.2 GA
            Reporter: Guenther Demetz
            Priority: Trivial
         Attachments: TestCaseQuryCache.jar

When using hibernate's query cache (hibernate.cache.use_query_cache),
then it's of fundamental importance to configure the Update Timestamps cache region in
a way that his entries survive longer than the cached result sets in the Query cache region.
Otherwise queries could return wrong (obsolete) result sets (See attached testcase).
This is because the current UpdateTimestampsCache#isUpToDate implementation considers a result-set also as up-to-date,
if there are no update-timestamps cached for the interested spaces (tables) at all.
It if therefore important to notice that:
1- The Update-Timestamps-Cache-Region elements max-size should be configured higher than the number of tables you have 
   on the db-schema, in manner that he can remember/hold the last update-timestamp for each table.
2- If you use any other eviction policy in the Update-Timestamps-Cache-Region, then you must assure 
   that cached result sets in the Query-cache-region are evicted before relevant update-timestamps are going to be evicted.

This fact should be clearly documented somewhere.
Thanks
G.D.


-- 
This message is automatically generated by JIRA.
-
If you think it was sent incorrectly contact one of the administrators: http://opensource.atlassian.com/projects/hibernate/secure/Administrators.jspa
-
For more information on JIRA, see: http://www.atlassian.com/software/jira