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https://issues.apache.org/jira/browse/FLINK-17545?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17107082#comment-17107082
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Aljoscha Krettek commented on FLINK-17545:
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Did you by chance also try this with Flink 1.9? Normally the different UDF
methods should not be called concurrently.
> Resource leak JDBCUpsertOutputFormat
> ------------------------------------
>
> Key: FLINK-17545
> URL: https://issues.apache.org/jira/browse/FLINK-17545
> Project: Flink
> Issue Type: Improvement
> Components: Connectors / JDBC
> Affects Versions: 1.10.0
> Reporter: John Lonergan
> Priority: Major
>
> See also FLINK-17544 for background to this scenario.
> Synchronisation in JDBCUpsertOutputFormat allows resources leaks.
> The close() method is synchronised with write() and flush() but not open.
> So if open() is a slow call (which in my case it occasionally is) then it may
> not be complete when close() is called.
> In this situation the open() method will eventually proceed to open resources
> such as database connections that will never be closed by the program.
> So if we are +not+ going to synchronise open() with the other methods then an
> alternative approach would be to have open() do a double check before
> returning.
> ie Just before open() completes it would need to synchonise and then check if
> close has already been called whilst open() was running.
> If so then open() should proceed to undo any resources it has just opened.
> One could perhaps argue that there's a problem with the state model if the
> framework might call close before open has completed; but I can imagine why
> this happens.
> However, the must therefore deal with the consequential complexity of this
> deal with the threading issues effectively.
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