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Posted to issues-all@impala.apache.org by "Sahil Takiar (Jira)" <ji...@apache.org> on 2020/09/02 17:44:00 UTC
[jira] [Commented] (IMPALA-6705) TotalNetworkSendTime in query
profile is misleading
[ https://issues.apache.org/jira/browse/IMPALA-6705?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17189580#comment-17189580 ]
Sahil Takiar commented on IMPALA-6705:
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I got bitten by this recently, and it was very confusing. Linking to IMPALA-10137. +1 on fixing this.
> TotalNetworkSendTime in query profile is misleading
> ---------------------------------------------------
>
> Key: IMPALA-6705
> URL: https://issues.apache.org/jira/browse/IMPALA-6705
> Project: IMPALA
> Issue Type: Bug
> Components: Distributed Exec
> Affects Versions: Impala 2.5.0, Impala 2.4.0, Impala 2.6.0, Impala 2.7.0, Impala 2.8.0, Impala 2.9.0, Impala 2.10.0, Impala 2.11.0, Impala 2.12.0
> Reporter: Michael Ho
> Priority: Major
> Labels: observability
>
> {{TotalNetworkSendTime}} is actually measuring the time which a fragment instance execution thread spent waiting for the completion of previous RPC. This is a combination of:
> - network time of sending the RPC payload to the destination
> - processing and queuing time in the destination
> - network time of sending the RPC response to the originating node
> The name of this metric itself is misleading because it gives the impression that it's the time spent sending the RPC payload to the destination so a query profile with a high {{TotalNetworkSendTime}} may easily mislead a user into concluding that there is something wrong with the network. In reality, the receiving end could be overloaded and it's taking a huge amount of time to respond to an RPC.
> For this metric to be useful, we need to have a breakdown of those 3 components above.
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