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From "Knut Anders Hatlen (JIRA)" <derby-...@db.apache.org>
Subject [jira] Commented: (DERBY-557) Client driver gets OutOfMemoryError when re-executing statement without closing ResultSet
Date Thu, 08 Sep 2005 15:40:30 GMT
    [ http://issues.apache.org/jira/browse/DERBY-557?page=comments#action_12322938 ] 

Knut Anders Hatlen commented on DERBY-557:
------------------------------------------

Quoting myself from derby-user:

> FYI, I had a look in the client driver code. It seems like only
> markClosed() is called on the open ResultSets when a statement is
> re-executed. The difference between close() and markClosed() is
> basically that close() additionally checks whether it should
> auto-commit, nulls out the cursor and meta data, and calls
>
>   connection_.CommitAndRollbackListeners_.remove(this);
>
> Could this be our memory leak? Is there any situation where one
> shouldn't call close() on the result sets when re-executing?

After I sent this mail, I ran a test with some println-statements in the client driver. When
the OutOfMemoryError was thrown the CommitAndRollbackListeners_ list had around 17000 elements
when using Statement, and around 300000 elements when using PreparedStatement.

> Client driver gets OutOfMemoryError when re-executing statement without closing ResultSet
> -----------------------------------------------------------------------------------------
>
>          Key: DERBY-557
>          URL: http://issues.apache.org/jira/browse/DERBY-557
>      Project: Derby
>         Type: Bug
>   Components: Network Client
>     Versions: 10.1.1.0, 10.1.2.0, 10.2.0.0
>     Reporter: Knut Anders Hatlen
>     Priority: Minor
>      Fix For: 10.1.2.0, 10.2.0.0

>
> When re-executing a statement without closing the old ResultSet, some of the old ResultSet's
resources are not released, and the network client will eventually get an OutOfMemoryError.
> Example:
> 	Connection c = DriverManager.getConnection("jdbc:derby://localhost/mydb");
> 	PreparedStatement ps = c.prepareStatement("select * from sys.systables");
> 	while (true) {
> 		ResultSet rs = ps.executeQuery();
> 	}
> This code will run for some time and then throw an OutOfMemoryError. Same thing happens
with Statement instead of PreparedStatement. If rs.close() is added in the loop, the code
works. Explicitly closing the ResultSet should not be necessary according to this quote from
the JDBC 3.0 spec:
>   For Select statements, the statement is complete when the associated result set is
closed. The result set is closed as soon as one of the following occurs:
>      - all of the rows have been retrieved
>      - the associated Statement object is re-executed
>      - another Statement object is executed on the same connection

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