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

[Strong Liu (JIRA)]

Performance risk: Suboptimal synchronization in org.hibernate.engine.query.QueryPlanCache.getHQLQueryPlan
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                 Key: HHH-5927
                 URL: http://opensource.atlassian.com/projects/hibernate/browse/HHH-5927
             Project: Hibernate Core
          Issue Type: Improvement
          Components: core
            Reporter: 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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