[jira] [Commented] (DBCP-345) NumActive is off-by-one at instantiation and causes premature exhaustion

["Mark Thomas (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/DBCP-345?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13886867#comment-13886867 ] 

Mark Thomas commented on DBCP-345:
----------------------------------

One other thing I thought of to help diagnose this is a debugger. If you put a break point on every place where numActive is incremented and then run your test you'll find out what is triggering the increment. If attaching a debugger isn't an option, you can modify the code, create a new exception every time numActive is incremented and then print the stack trace for that exception to the console. It isn't the prettiest debugging technique but it will tell what is triggering the behaviour you see.

> NumActive is off-by-one at instantiation and causes premature exhaustion
> ------------------------------------------------------------------------
>
>                 Key: DBCP-345
>                 URL: https://issues.apache.org/jira/browse/DBCP-345
>             Project: Commons Dbcp
>          Issue Type: Bug
>    Affects Versions: 1.4
>            Reporter: Kevin Ross
>         Attachments: AssertNumActiveDataSource.java, DebugBasicDataSource.java, DebugConnectionPool.java, dbcp-345.patch
>
>   Original Estimate: 1h
>  Remaining Estimate: 1h
>
> Scenario: we have some code that we had thought was potentially leaking connections.  In our unitTest/integrationTest environment, we know we can *lock down connections to a total of 2* and a full run should pass.  We had no such luck with a {{maxActive}} of 2.    
> We created/attached a {{DebugBasicDataSource}} which initializes a  {{DebugConnectionPool}} for logging purposes and delegates into the DBCP hierarchy.  BTW - consistent use of accessors would have made this a cleaner affair ;) 
> {code}        // num active starts at one! Here is the original unmodified log message:
>         //          BORROWING:  from AbandonedObjectPool@10f0f6ac (1 of 2) 0 idle: threadStats[ ]: all-time uniques{ (empty)  }
>         // SEE! no borrows ever, and the first pre-borrow already has a count of 1!{code}
> Before borrowing the first connection - {{numActive}} is 1!  
> The gorier details below, I hope they help someone else!
> Constraining the pool was the best way to uncover the leakage.  
> Thinking it was our error, we went after our code to find the problem.  We had such a hard time understanding who was using connections, in which Spring context.  The confusion stemmed from the fact that our unitTests run against REST resources deployed as Jersey components in a Grizzly container.  Where they using the same connection pool or not?  Was the unitTest setup side exhausting more connections, or was it leaking on the REST service side.
> Answers: 
> 1.  Our unitTests executing Jersey with in-VM Grizzly container do indeed utilize the same pool (and same Spring context).
> 2.  Our unitTest (side) was not using more than one connection for data setup, and it returned the connection for reuse.
> 3.  Our REST service side was only using one connection, but was a Grizzly threaded container and we have AcitveMQ running as well.  Practically, one server connection could handle everything, but the REST service and ActiveMQ listener could potentially claim 2.
> Note, the attached DebugBasicDataSource was quite useful to determine which threads were claiming which connections in a leak situation.  Certainly do not configure it on the production side, but it might be nice to see something like this offered up on the DBCP site somewhere to help developers find or confirm their misconfiguration or bad code.



--
This message was sent by Atlassian JIRA
(v6.1.5#6160)