[hibernate-issues] [Hibernate-JIRA] Commented: (HHH-4550) Document that update-timestamps cache region should not be configured for expiry.
[
http://opensource.atlassian.com/projects/hibernate/browse/HHH-4550?page=c...
]
Adrien commented on HHH-4550:
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http://www.ehcache.org/documentation/user-guide/hibernate
With the new global pool of object (specifing the total memory size instead of the size of
each cache size) in ehCache 2.5, specifing that the cache should not expired is not
enough. The cache may be cleared if the other caches are used. It is important to pinned
the cache, to ensure it won't be clear. We could be confident that, even with the
cache spinned, it won't explode, since the number of hibernate "space" is
not infinite.
<ehcache maxBytesLocalHeap="500M">
<cache name="org.hibernate.cache.UpdateTimestampsCache"
eternal="true" overflowToDisk="false">
<pinning store="inCache" />
</cache>
</ehcache>
Document that update-timestamps cache region should not be configured
for expiry.
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Key: HHH-4550
URL: http://opensource.atlassian.com/projects/hibernate/browse/HHH-4550
Project: Hibernate ORM
Issue Type: Improvement
Components: documentation
Affects Versions: 3.3.2
Environment: 3.3.2 GA
Reporter: Guenther Demetz
Assignee: Steve Ebersole
Priority: Trivial
Fix For: 3.3.x, 3.5.0-Beta-3
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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