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This is an automatically generated e-mail. To reply, visit:
https://reviews.apache.org/r/55178/
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Review request for Ambari, Nate Cole, Sebastian Toader, and Sid Wagle.
Bugs: AMBARI-19364
https://issues.apache.org/jira/browse/AMBARI-19364
Repository: ambari
Description
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Recently I noticed that collections coming back from JPA were using a
{{Vector}} as their concrete collection. This seems very wrong as {{Vector}} is
a completely synchronized collection.
Tracing through EclipseLink, it seems like this really only affects
[ReadAllQuery|http://grepcode.com/file/repo1.maven.org/maven2/org.eclipse.persistence/eclipselink/2.5.2/org/eclipse/persistence/queries/ReadAllQuery.java/#68].
Essentially, EclipseLink uses a
[ContainerPolicy|http://grepcode.com/file/repo1.maven.org/maven2/org.eclipse.persistence/eclipselink/2.5.2/org/eclipse/persistence/internal/queries/ContainerPolicy.java#ContainerPolicy]
to determine how the result set should be collected. There are policies for
{{Vector}}, {{ArrayList}}, {{HashSet}}, etc.
The interesting part here is that this really only affects the {{ReadAllQuery}}
which is used by JPA's {{Query#getResultList()}} ... anytime it needs to create
a collection of entities, it's going to use a {{Vector}}.
There's actually very little documentation on this. In fact, the only way to
change this is either set a global value for the default container policy, or
set a per-query policy. An example of setting the global policy would be:
{code}
public class EclipseLinkSessionCustomizer implements SessionCustomizer {
/**
* {@inheritDoc}
* <p/>
* This class exists for quick customization purposes.
*/
@Override
public void customize(Session session) throws Exception {
// ensure db behavior is same as shared cache
DatabaseLogin databaseLogin = (DatabaseLogin) session.getDatasourceLogin();
databaseLogin.setTransactionIsolation(DatabaseLogin.TRANSACTION_READ_COMMITTED);
// for some reason, read-all queries use a Vector as their container for
// result items - this seems like an unnecessary performance hit since
// Vectors are synchronized and there's no apparent reason to provide a
// thread-safe collection on a read all query
ContainerPolicy.setDefaultContainerClass(CoreClassConstants.ArrayList_class);
}
}
{code}
This indeed causes collections returned by queries to be backed by ArrayLists.
There is some discussion on this topic already:
https://bugs.eclipse.org/bugs/show_bug.cgi?id=255634
It seems like this was kept as a {{Vector}} purely for backward compatibility
reasons.
Diffs
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ambari-server/src/main/java/org/apache/ambari/server/orm/EclipseLinkSessionCustomizer.java
6717e01
Diff: https://reviews.apache.org/r/55178/diff/
Testing
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Ran a full deployment and didn't see any issues. Verfied that ArrayList are
returned in `ReadAllQuery` instead of Vector.
Thanks,
Jonathan Hurley
