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From "Deepa Remesh (JIRA)" <derby-...@db.apache.org>
Subject [jira] Updated: (DERBY-210) Network Server will leak prepared statements if not explicitly closed by the user until the connection is closed
Date Tue, 14 Feb 2006 19:57:10 GMT
     [ http://issues.apache.org/jira/browse/DERBY-210?page=all ]

Deepa Remesh updated DERBY-210:
-------------------------------

    Attachment: derby-210-patch4-v2.diff
                derby-210-patch4-v2.status

Attaching a patch 'derby-210-patch4-v2.diff' which fixes the finalization code in Statement
classes in client driver. This patch is in preparation for the fixes to memory leaks. 

Summary of changes: 

* Changes the finalizers in Statement classes to do only client-side cleanup. No network operations
are done in the finalizers.

* Adds markClosed method to PreparedStatement class which overrides the markClosed method
in Statement class. All client-side cleanup code is moved to markClosed method. Two forms
of markClosed method are added:

    - markClosed() method will perform clean up but will not remove Statement from the open
statements list and PreparedStatement from the commit and rollback listeners list in org.apache.derby.client.am.Connection.
This method is called from finalize(), Connection#markStatementsClosed(), and to close positioned
update statements. For the finaizer to be called, the Statement should not have any references
and so it should have been already removed from the lists.  Connection#markStatementsClosed
method explicitly removes the Statement from open statements list. Positioned update statements
are not added to the open statements list. Hence, markClosed() is called in these cases.

    - markClosed(true) will additionally remove the statement objects from the lists. This
is called from close() method.

* After these changes, it is not required to override close(), closeX() and finalize() methods
in PreparedStatement class since they contain same code as in Statement class. So these methods
are removed.

With these changes, I ran derbynetclientmats with Sun JDK 1.4.2. jdbcapi/dbMetaDataJdbc30.java
failed. This test has been already fixed by David. 

Please take a look at this patch. Thanks.

> Network Server will leak prepared statements if not explicitly closed by the user until
the connection is closed
> ----------------------------------------------------------------------------------------------------------------
>
>          Key: DERBY-210
>          URL: http://issues.apache.org/jira/browse/DERBY-210
>      Project: Derby
>         Type: Bug
>   Components: Network Client
>     Reporter: Kathey Marsden
>     Assignee: Deepa Remesh
>  Attachments: DOTS_ATCJ2_Derby-noPatch.png, DOTS_ATCJ2_Derby-withPatch.png, derby-210-patch1.diff,
derby-210-patch2.diff, derby-210-patch2.status, derby-210-patch3.diff, derby-210-patch4-v2.diff,
derby-210-patch4-v2.status, derby-210-v2-draft.diff, derby-210-v2-draft.status, derbyStress.java
>
> Network server will not garbage collect prepared statements that are not explicitly closed
by the user.  So  a loop like this will leak.
> ...
> PreparedStatement ps;
>  for (int i = 0 ; i  < numPs; i++)
> 	{
> 	 ps = conn.prepareStatement(selTabSql);
> 	 rs =ps.executeQuery();
> 	 while (rs.next())
> 	{
> 	    rs.getString(1);
> 	}
> 	rs.close();
> 	// I'm a sloppy java programmer
> 	//ps.close();
> 	}
> 			
> To reproduce run the attached program 
> java derbyStress
> Both client and server will grow until the connection is closed.
>  
> It is likely that the fix for this will have to be in the client.  The client does not
send protocol to close the prepared statement, but rather reuses the PKGNAMCSN on the PRPSQLSTT
request once the prepared statement has been closed. This is how the server knows to close
the old statement and create a new one.

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