[hibernate-issues] [Hibernate-JIRA] Commented: (HHH-4550) query cache: Attention with configuring Update Timestamps Cache region: expired entries cause wrong result sets!
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http://opensource.atlassian.com/projects/hibernate/browse/HHH-4550?page=c...
]
Guenther Demetz commented on HHH-4550:
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Finally in the JavaDoc of class UpdateTimestampsCache I have found more less the advice I
searched for:
/**
...
* It is important that the cache timeout of the underlying cache implementation be set
* to a higher value than the timeouts of any of the query caches. In fact, we
* recommend that the the underlying cache not be configured for expiry at all.
* Note, in particular, that an LRU cache expiry policy is never appropriate.
...
*/
public class UpdateTimestampsCache ...
Personally I think this hint should appear in every article speaking about configuring
hibernate query cache.
query cache: Attention with configuring Update Timestamps Cache
region: expired entries cause wrong result sets!
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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.
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