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From "John Huss (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CAY-1864) Process threads waiting for an available DB connection in the order they came in
Date Thu, 19 Dec 2013 22:46:09 GMT

    [ https://issues.apache.org/jira/browse/CAY-1864?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13853416#comment-13853416
] 

John Huss commented on CAY-1864:
--------------------------------

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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