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https://issues.apache.org/jira/browse/IMPALA-15012?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=18085377#comment-18085377
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ASF subversion and git services commented on IMPALA-15012:
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Commit 5fed4392f0d4b8a43efffbc590f2727834de094a in impala's branch
refs/heads/master from m-sanjana19
[ https://gitbox.apache.org/repos/asf?p=impala.git;h=5fed4392f ]
IMPALA-15012: [DOCS] Documentation for client-side bottleneck
identification
Updates the performance tuning docs to cover the following
ImpalaServer query profile metrics:
- ClientFetchWaitTimer & ClientFetchWaitTimeStats
- ClientFetchLockWaitTimer
- GetInFlightProfileTimeStats
Explains how a high ClientFetchWaitTimer is relative to
total query duration indicates the client is slow to
fetch results, which backpressures Impala's pipelined execution.
Change-Id: Iaaf2e4cc069c2af9f66b30175d43b8abb30036c0
Reviewed-on: http://gerrit.cloudera.org:8080/24385
Tested-by: Impala Public Jenkins <[email protected]>
Reviewed-by: Quanlong Huang <[email protected]>
> Doc for client-side bottleneck
> ------------------------------
>
> Key: IMPALA-15012
> URL: https://issues.apache.org/jira/browse/IMPALA-15012
> Project: IMPALA
> Issue Type: Documentation
> Components: Docs
> Reporter: Quanlong Huang
> Assignee: Sanjana Malhotra
> Priority: Critical
>
> We need document for how to identify client-side bottlenecks. We can add
> content in the section of "Using the Query Profile for Performance Tuning" in
> this page:
> [https://impala.apache.org/docs/build/asf-site-html/topics/impala_explain_plan.html]
> There is a section of ImpalaServer in the query profile which has these
> counters:
> * ClientFetchWaitTimer: Total time spent returning rows to the client and
> other client-side processing.
> * ClientFetchWaitTimeStats: Summary stats for client fetch wait time.
> * ClientFetchLockWaitTimer: Cumulative time client fetch requests waiting for
> locks.
> * GetInFlightProfileTimeStats: Summary stats of the time dumping profiles
> when the query is still in-flight.
> If the ClientFetchWaitTimer is close to the total query duration, it means
> the bottleneck is on the client side; the Impala server is simply waiting for
> the client to fetch the query results. Note that while client is fetching
> results, the query state is FINISHED. It doesn't mean the client has fetched
> all the rows. Due to the nature of pipeline execution in Impala, subsequent
> results cannot be produced or computed if the already generated results are
> not fetched. The FINISHED state just means client can start fetching results
> from Impala.
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