[hibernate-issues] [Hibernate-JIRA] Commented: (HHH-5927) Performance risk: Suboptimal synchronization in org.hibernate.engine.query.QueryPlanCache.getHQLQueryPlan

[Andres (JIRA)]

    [ http://opensource.atlassian.com/projects/hibernate/browse/HHH-5927?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=44548#comment-44548 ] 

Andres commented on HHH-5927:
-----------------------------

Hi, 
we are using Hibernate 3.6.8 in our application and we are also experiencing performance problems with QueryPlanCache.getHQLQueryPlan and QueryPlanCache.getNativeSQLQueryPlan. Profiling the code shows that threads are blocking at SoftLimitMRUCache.get(Object). 

I would love to see this issue fixed in next 3.6.* release.

Is there any ways I could help?
I tried to test if fixes at https://github.com/Sanne/hibernate-core/tree/HHH-5927-part would improve performance... but then I realized that these fixes are on 4.* branch only. We definitely can't switch to Hibernate 4.

> Performance risk: Suboptimal synchronization in org.hibernate.engine.query.QueryPlanCache.getHQLQueryPlan
> ---------------------------------------------------------------------------------------------------------
>
>                 Key: HHH-5927
>                 URL: http://opensource.atlassian.com/projects/hibernate/browse/HHH-5927
>             Project: Hibernate Core
>          Issue Type: Improvement
>          Components: core
>            Reporter: Strong Liu
>            Assignee: Strong Liu
>         Attachments: hotspot.png
>
>
> with Order Demo (real-life simulation attempt test app) I have noticed that there is thread contention on createNamesQuery() which sounds suspicious.
> After investigation it boils down to org.hibernate.engine.query.QueryPlanCache.getHQLQueryPlan. It serves as a cache (internal, not replacable) for queries using LRU algorithm (supplied from Apache utils).
> Generally speaking, blocking threads in any sort of caches indicates a problem. From about 2000 calls, 700 got blocked (which is also not nice for context switching).
> I guess, one of the problems is that there is exclusive synchronization in get method:
> public synchronized Object get(Object key) {...}
> which could be replaced by a more granular read-write lock.
> org/hibernate/engine/query/QueryPlanCache.java
> org/hibernate/util/SoftLimitMRUCache.java

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