[Impala-ASF-CR] IMPALA-6813: Hedged reads metrics broken when scanning non-HDFS based table

["Sailesh Mukil (Code Review)" <ge...@cloudera.org>]

Sailesh Mukil has posted comments on this change. ( http://gerrit.cloudera.org:8080/9966 )

Change subject: IMPALA-6813: Hedged reads metrics broken when scanning non-HDFS based table
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Patch Set 1:

> > Patch Set 1:
 > >
 > > > Patch Set 1:
 > > >
 > > > I haven't added a custom cluster test for this since hedged
 > reads are not deterministic, and we'd be dealing with a bunch of
 > flakiness.
 > >
 > > I'm uncomfortable that we've got a flag with no testing of the
 > code path behind it.
 > >
 > > Can you force a hedged read by "kill -STOP"'ing a datanode before
 > the query and "kill -CONT" afterwards?
 > 
 > Thanks for the suggestion, Phil. I will try this.

I picked this up again and spent some time trying to force hedged reads. However, I found that even if you SIGSTOP any combination of DataNodes while leaving only one running, and then run a query against HDFS, since all the DataNodes are on the same node in a minicluster, it doesn't count them as hedged reads.

This means that we can only have a hedged read test in a remote cluster setting.


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Gerrit-Project: Impala-ASF
Gerrit-Branch: master
Gerrit-MessageType: comment
Gerrit-Change-Id: I48fe80dfd9a1ed68a8f2b7038e5f42b5a3df3baa
Gerrit-Change-Number: 9966
Gerrit-PatchSet: 1
Gerrit-Owner: Sailesh Mukil <sa...@cloudera.com>
Gerrit-Reviewer: Philip Zeyliger <ph...@cloudera.com>
Gerrit-Reviewer: Sailesh Mukil <sa...@cloudera.com>
Gerrit-Comment-Date: Mon, 21 May 2018 21:56:39 +0000
Gerrit-HasComments: No