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https://issues.apache.org/jira/browse/SPARK-8008?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14567240#comment-14567240
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Rene Treffer commented on SPARK-8008:
-------------------------------------

I've seen very poor performance when streaming it as one partition for example 
("WHERE 1=1"). I'll retry with different partition counts.

But I still think there should be a warning about the behavior, as I didn't 
naturally understand that partition count == parallelism in this case (although 
it's logical after some thinking).

> sqlContext.jdbc can kill your database due to high concurrency
> --------------------------------------------------------------
>
>                 Key: SPARK-8008
>                 URL: https://issues.apache.org/jira/browse/SPARK-8008
>             Project: Spark
>          Issue Type: Bug
>            Reporter: Rene Treffer
>
> Spark tries to load as many partitions as possible in parallel, which can in 
> turn overload the database although it would be possible to load all 
> partitions given a lower concurrency.
> It would be nice to either limit the maximum concurrency or to at least warn 
> about this behavior.



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