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https://issues.apache.org/jira/browse/CAY-1864?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13853416#comment-13853416
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John Huss commented on CAY-1864:
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I've got tomcat-jdbc in my project now, so I'm going to try that rather than
continue improving PoolManager. One issue I had with integrating tomcat-jdbc
is that if you configure your data source using cayenne's properties (like
cayenne.jdbc.driver) then it switches your DataSourceFactory to
PropertyDataSourceFactory even if you have entered a custom factory in your
cayenne.xml file. I'd suggest that cayenne should only override the factory if
it is the default value - XMLPoolingDataSourceFactory.
As a workaround I renamed my properties (which I am still using). But it would
be nicer to have the same property names and be able to switch connection pool
implementations merely by changing the DataSourceFactory.
> Process threads waiting for an available DB connection in the order they came
> in
> --------------------------------------------------------------------------------
>
> Key: CAY-1864
> URL: https://issues.apache.org/jira/browse/CAY-1864
> Project: Cayenne
> Issue Type: Improvement
> Components: Core Library
> Affects Versions: 3.2M1
> Reporter: John Huss
> Assignee: John Huss
> Attachments:
> 0001-CAY-1864-Process-threads-waiting-for-an-available-DB.patch
>
>
> Currently when all the DB connections in the pool are used up threads will
> wait for available connection. As connections become available they are
> given to essentially random threads, not the thread that was waiting first.
> This causes somewhat erratic behavior since some requests will come in and
> get a connection right away even though others have been waiting for a long
> time, eventually causing more threads to throw exceptions than may have been
> necessary if requests were processed in order.
> Particularly in cases with large but brief spikes in activity - errors may be
> wholly avoided if requests are processed in order where otherwise they could
> produce many failures. I have observed this in my testing.
> I have a patch I am testing out. It creates a queue to keep track of the
> waiting threads and then grant them connections in order.
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