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Ship it! Ship It! - Nate Cole On Jan. 4, 2017, 11:56 a.m., Jonathan Hurley wrote: > > ----------------------------------------------------------- > This is an automatically generated e-mail. To reply, visit: > https://reviews.apache.org/r/55178/ > ----------------------------------------------------------- > > (Updated Jan. 4, 2017, 11:56 a.m.) > > > 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 > ------- > > 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 > ----- > > > ambari-server/src/main/java/org/apache/ambari/server/orm/EclipseLinkSessionCustomizer.java > 6717e01 > > Diff: https://reviews.apache.org/r/55178/diff/ > > > Testing > ------- > > Ran a full deployment and didn't see any issues. Verfied that ArrayList are > returned in `ReadAllQuery` instead of Vector. > > > Thanks, > > Jonathan Hurley > >
