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

[Strong Liu (JIRA)]

    [ https://hibernate.onjira.com/browse/HHH-5927?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=45643#comment-45643 ] 

Strong Liu commented on HHH-5927:
---------------------------------

Eric,

it seems your impl won't work, since 
{quote}
CacheBuilder.softValues(), which wraps values in soft references. Softly referenced objects are garbage-collected in a globally least-recently-used manner, in response to memory demand. Unless you are very familiar with the behavior of soft references, we recommend using the more predictable maximum cache size instead. Use of softValues() will cause values to be compared using identity (==) equality instead of equals(). 
{quote}

the key instance, HqlQueryPlanKey, for example, is created by every get, so it will always miss the soft 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

--
This message is automatically generated by JIRA.
For more information on JIRA, see: http://www.atlassian.com/software/jira