[hibernate-issues] [Hibernate-JIRA] Commented: (HHH-5927) Performance risk: Suboptimal synchronization in org.hibernate.engine.query.QueryPlanCache.getHQLQueryPlan
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https://hibernate.onjira.com/browse/HHH-5927?page=com.atlassian.jira.plug...
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Strong Liu commented on HHH-5927:
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{quote}
So the problem with MapMaker is you're completely giving up the max-size configuration
and relying solely on the GC to cleanup
..........
{quote}
{quote}
Also in your gist you set concurrency to 1, are you really only expecting 1 thread to
update the table at a time?
{quote}
I guess you're talking about _StatefulPersistenceContext_?
yes, this is not supposed to be thread safe, as same as _Session_.
and in this case, the Map used within _StatefulPersistenceContext_ is not a cache, but a
map, so we can't using any eviction policy here.
Performance risk: Suboptimal synchronization in
org.hibernate.engine.query.QueryPlanCache.getHQLQueryPlan
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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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