[hibernate-issues] [Hibernate-JIRA] Commented: (HHH-3195) session.clear() is not effective when use_query_cache is true

[Chris Brown (JIRA)]

    [ http://opensource.atlassian.com/projects/hibernate/browse/HHH-3195?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=32424#action_32424 ] 

Chris Brown commented on HHH-3195:
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Sadly, calling executeActions does not cause the references to be released - if you put a breakpoint in executeActions, you'll see that it is called on a regular flush anyway. I have had success getting Hibernate to release the references by calling this after session.clear():

((SessionImpl)session).getActionQueue().afterTransactionCompletion(true)

If you are only doing inserts I think this should be a fairly safe solution, because the afterTransactionCompletion hook for an insert just updates the 2nd level cache, which you should have disabled anyway.


The problem is due to the fact that the ActionQueue finds out whether the cache is enabled by calling:

session.getFactory().getSettings().isQueryCacheEnabled()

It seems to me that this check should also take into account whether the second-level cache is enabled, and the current cache mode of the session.


> session.clear() is not effective when use_query_cache is true
> -------------------------------------------------------------
>
>                 Key: HHH-3195
>                 URL: http://opensource.atlassian.com/projects/hibernate/browse/HHH-3195
>             Project: Hibernate Core
>          Issue Type: Bug
>    Affects Versions: 3.2.6
>         Environment: 3.2.6.ga, MySQL5
>            Reporter: James Berry
>
> As discussed in detail in http://forum.hibernate.org/viewtopic.php?t=944918, performing many inserts while use_query_cache is enabled will eventually cause an out of memory condition, even if the session is periodically flushed and cleared. That forum thread describes a potential root cause for this problem. Nobody from the Hibernate team has responded regarding the forum thread, even though it's been alive for three years now!
> Note that an answer to "disable the query cache" is not a good solution to the problem, as we need the query cache elsewhere. If it were possible to disable the query cache for a particular session, that would be fine, but I see no way do that.

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