[jira] Updated: (DERBY-3596) Creation of logical connections from a pooled connection causes resource leak on the server

["Kristian Waagan (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/DERBY-3596?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Kristian Waagan updated DERBY-3596:
-----------------------------------

    Attachment: derby-3596-1a-complex_approach.diff
                derby-3596-2a-simple_approach.diff

I have uploaded two fixes that solve the problem.
None of them are ready for commit, but I'd like to get some comments
on which approach to go for.

* 'derby-3596-1a-complex_approach.diff'
  Solves the problem by maintaining only one physical connection on the
  server side. This connection has to be reset, which includes setting
  the isolation level, resetting IDENTITY_VAL_LOCAL and cleaning out
  temporary tables.
  The patch basically contains two parts: Detecting and handling a
  deferred reset in DRDAConnThread and exposing / extending reset
  functionality (the connection classes).
  A drawback of this approach is that care must be taken to get the
  reset logic correct.

* 'derby-3596-2a-simple_approach.diff'
  Solves the problem by simply closing the existing connection on the
  server side before creating a new, if there is one.
  Only a few lines of code.
  This solution is far from optimal, since a physical connection is both
  closed and created on the server for each logical connection on the
  client side.

* Optimal approach
  This would probably be to rewrite the whole logic, both on the client
  and the server side. It seems to me there is half-baked support for a
  lot more advanced functionality than what we are using. I see what we
  have / had as a first step towards supporting enterprise multi-tiered
  connection pooling ala what DB2 has. There is support for this in
  DRDA, where for instance a pooling agent can use a single connection
  to do work for multiple clients/drivers (one must switch database and
  user "on the fly").

I'll attach a few graphs showing the heap usage of the various
approaches, and also provide a few numbers regarding performance.

I'm asking for comments on this issue!


> 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
>         Attachments: ConnectionPoolingBug.java, derby-3596-1a-complex_approach.diff, derby-3596-2a-simple_approach.diff
>
>
> 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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