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Posted to issues-all@impala.apache.org by "Sahil Takiar (Jira)" <ji...@apache.org> on 2020/09/02 20:25:00 UTC
[jira] [Commented] (IMPALA-10139) Slow RPC logs can be misleading
[ https://issues.apache.org/jira/browse/IMPALA-10139?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17189696#comment-17189696 ]
Sahil Takiar commented on IMPALA-10139:
---------------------------------------
Linking IMPALA-3380 - which has some details why we don't add timeouts for TransmitData RPCs.
> Slow RPC logs can be misleading
> -------------------------------
>
> Key: IMPALA-10139
> URL: https://issues.apache.org/jira/browse/IMPALA-10139
> Project: IMPALA
> Issue Type: Improvement
> Reporter: Sahil Takiar
> Priority: Major
>
> The slow RPC logs added in IMPALA-9128 are based on the total time taken to successfully complete a RPC. The issue is that there are many reasons why an RPC might take a long time to complete. An RPC is considered complete only when the receiver has processed that RPC.
> The problem is that due to client-driven back-pressure mechanism, it is entirely possible that the receiver RPC does not process a receiver RPC because {{KrpcDataStreamRecvr::SenderQueue::GetBatch}} just hasn't been called yet (indirectly called by {{ExchangeNode::GetNext}}).
> This can lead to flood of slow RPC logs, even though the RPCs might not actually be slow themselves. What is worse is that the because of the back-pressure mechanism, slowness from the client (e.g. Hue users) will propagate across all nodes involved in the query.
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