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

[Eric Dalquist (JIRA)]

    [ https://hibernate.onjira.com/browse/HHH-5927?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=45653#comment-45653 ] 

Eric Dalquist commented on HHH-5927:
------------------------------------

Sorry I just realized I was looking at the wrong part of that patch. Your QPC code looks good, the only thing is your onRemoval should only copy the removed entry to the soft reference cache if the entry was evicted "notification.wasEvicted()" otherwise any remove or clear operation on any of your caches will result in all of the removed/cleared entries getting moved into the soft reference cache.

> Performance risk: Suboptimal synchronization in org.hibernate.engine.query.QueryPlanCache.getHQLQueryPlan
> ---------------------------------------------------------------------------------------------------------
>
>                 Key: HHH-5927
>                 URL: https://hibernate.onjira.com/browse/HHH-5927
>             Project: Hibernate ORM
>          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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