Martin Grigorov created ISIS-1134:
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Summary: 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 a use case. 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 ObjectAdapter, 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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