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https://issues.apache.org/jira/browse/ISIS-1134?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14500668#comment-14500668
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Martin Grigorov commented on ISIS-1134:
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org.apache.isis.core.metamodel.services.container.DomainObjectContainerDefault#firstMatch(org.apache.isis.applib.query.Query<T>)
starts with flush() call.
Why this is needed? Why by default?
It looks like a custom transaction isolation mechanism.
Removing this #flush() call fixes the issue above and my app seems to work
fine. But I'm sure some applications' use cases must be broken now.
> DN connections leak due to non-closed queries (?!)
> --------------------------------------------------
>
> Key: ISIS-1134
> URL: https://issues.apache.org/jira/browse/ISIS-1134
> Project: Isis
> Issue Type: Bug
> Components: Core
> Affects Versions: core-1.8.0
> Reporter: Martin Grigorov
> Assignee: Dan Haywood
>
> My application failed twice with OutOfMemoryError in heap space so I've
> dumped a .hprof of its memory (jmap -dump:format=b,file=some-file.hprof) and
> analyzed it with Eclipse MAT (https://eclipse.org/mat/).
> It appears that there are many org.datanucleus.store.rdbms.query.JDOQLQuery$2
> objects.
> JDOQLQuery$2 appears to be ManagedConnectionResourceListener (
> https://github.com/datanucleus/datanucleus-rdbms/blob/651c77ff3b2af76ada97d14b537cd41fb0524a0c/src/java/org/datanucleus/store/rdbms/query/JDOQLQuery.java#L740).
> The listener is removed only when
> org.datanucleus.store.query.AbstractQueryResult#close() method is called.
> org.apache.isis.objectstore.jdo.datanucleus.persistence.queries.PersistenceQueryFindAllInstancesProcessor#process()
> does:
> {code}
> final List<?> pojos = (List<?>) jdoQuery.execute();
> return loadAdapters(specification, pojos);
> {code}
> So it consumes the result and returns ObjectAdapter for each pojo but it
> doesn't close the Query.
> AFAIK open-session-in-view pattern is not used in Isis so the resources
> should be closed explicitly after usage.
> A simple solution is to try/finally this code and close the query but I may
> miss some detail here.
> Related: recently I've profiled the application with Yourkit and it showed
> that DomainObjectContainer#allMatches() method is slow in one of the use
> cases. Some quick investigation showed that DomainObjectContainer delegates
> the work to
> org.apache.isis.objectstore.jdo.datanucleus.persistence.queries.PersistenceQueryProcessor#process().
> It loads the POJOs from the DB, then wraps them in ObjectAdapters, and
> finally
> org.apache.isis.core.metamodel.services.container.DomainObjectContainerDefault#allMatches(org.apache.isis.applib.query.Query<T>)
> unwraps them back to POJOs.
> Why this is done?
> This solves the issue of "consume the QueryResult before closing it" for the
> memory leak issue but it also adds to the processing time.
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