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https://issues.apache.org/jira/browse/DERBY-3596?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12599290#action_12599290
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Kristian Waagan commented on DERBY-3596:
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Thanks for looking at the issue Kathey.
I'll include the Jira number in the relevant comments when I post an updated
patch.
I agree that the simple fix seems less risky. I get one error when I run the
regression tests with it. The failure is in one of the new tests I wrote for
JDBC statement pooling, so I have to look into the test and also check how
statement pooling is affected by the fix.
I do have some reservations about the more complex fix. Even though the
approach is more optimal, the implementation is a bit hacky due to
compatibility constraints. I wonder if it would be better to design and
implement a proper mechanism at a later time.
Will we ever roll a compatibility breaking release? If not, we have to code
this using version checking and keep multiple implementations on both the
client and server side.
Also, please note that there are more alternatives than the two I have
suggested here. For instance, today we have Database and XADatabase. It might
be possible to introduce a PoolingDatabase, taken we can detect when clients
are indeed working with pooled connections. The difference between this one and
the current complex fix, would be that the former would map client logical
connections onto embedded logical connections, whereas the latter would map
client logical connections directly onto a single embedded physical connection.
This has some implications regarding connection state reset and object creation.
I'll work a bit more on the test failure and getting a better grip on things.
Feel free to add more comments.
> Creation of logical connections from a pooled connection causes resource leak
> on the server
> -------------------------------------------------------------------------------------------
>
> Key: DERBY-3596
> URL: https://issues.apache.org/jira/browse/DERBY-3596
> Project: Derby
> Issue Type: Bug
> Components: Network Client, Network Server, Performance
> Affects Versions: 10.1.3.1, 10.2.2.0, 10.3.2.1, 10.4.1.3, 10.5.0.0
> Reporter: Kristian Waagan
> Assignee: Kristian Waagan
> Attachments: complex-fix-heap.png, ConnectionPoolingBug.java,
> derby-3596-1a-complex_approach.diff, derby-3596-2a-simple_approach.diff,
> nofix-heap.png, simple-fix-heap.png
>
>
> When using ClientConnectionPoolDataSource and connection pooling, a new
> connection / transaction is created for every new logical connection, and the
> resources are not freed / cleaned up in the server. They are not even cleaned
> up when the physical connection (ClientPooledConnection) is closed.
> A logical connection is obtained by invoking
> ClientPooledConnection.getConnection().
> I have observed that if you run the repro enough times against the same
> server, the number of transaction in the transaction table will be reduced
> now and then. I believe this is garbage collection, but I have not
> investigated the problem enough to tell for sure what's going on.
> I have also seen some locks not being freed, causing timeouts in some
> applications. I don't have a repro for the lock problem at this time, but it
> is very likely related to this issue.
> Note that XA connections are handled differently on the server, and do
> probably not have this problem.
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