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https://issues.apache.org/jira/browse/HAWQ-1464?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16007336#comment-16007336
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Oleksandr Diachenko commented on HAWQ-1464:
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In current architecture of HAWQ+PXF, PXF agents are stateless and all mapping
fragments to certain PXF agents is being done on HAWQ master side. It seems to
me that concurrency limiting should be implemented in outer context rather than
on PXF.
> JDBC-PXF - support concurrency limiting
> ---------------------------------------
>
> Key: HAWQ-1464
> URL: https://issues.apache.org/jira/browse/HAWQ-1464
> Project: Apache HAWQ
> Issue Type: Sub-task
> Components: PXF
> Reporter: Michael Andre Pearce
> Assignee: Vineet Goel
>
> The external table definition doesn't limit how many concurrent queries can
> be executed on the remote server. It would be pretty simple to create a
> single external table using PXF JDBC that would issue thousands of concurrent
> queries to a single source database when doing a single SELECT in HAWQ.
> Initially, we should add a max_queries variable to the configuration file
> that I'm suggesting, that will reject queries from proceeding when a greater
> number of PXF instances are being requested than the max_queries variable.
> Longer term, we should implement a queueing system so we can support external
> tables that partitions data from the source at a very small grain but without
> killing the source database.
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