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 ...................................................................... Patch Set 4: > > preads add some overhead to HDFS, since it sends out redundant > read > > requests to replicas. Having it on by default might cause some > > confusion while running multiple heavy concurrent workloads. > > You're talking about hedged reads, not preads. We can use pread > with hedge reads on or off. So that can't be the blocker. You're right, however the knob to turn on hedged reads is a cluster wide setting and not an Impala only setting. So if any other component in the ecosystem (Hive, etc.) requires hedged reads turned on, and we (Impala) have preads() enabled by default, we'll end up doing hedged reads every time too. IIRC, that was the initial reasoning behind controlling preads()with a flag. -- To view, visit http://gerrit.cloudera.org:8080/9966 To unsubscribe, visit http://gerrit.cloudera.org:8080/settings Gerrit-Project: Impala-ASF Gerrit-Branch: master Gerrit-MessageType: comment Gerrit-Change-Id: I48fe80dfd9a1ed68a8f2b7038e5f42b5a3df3baa Gerrit-Change-Number: 9966 Gerrit-PatchSet: 4 Gerrit-Owner: Sailesh Mukil <sail...@cloudera.com> Gerrit-Reviewer: Dan Hecht <dhe...@cloudera.com> Gerrit-Reviewer: Impala Public Jenkins <impala-public-jenk...@cloudera.com> Gerrit-Reviewer: Philip Zeyliger <phi...@cloudera.com> Gerrit-Reviewer: Sailesh Mukil <sail...@cloudera.com> Gerrit-Reviewer: Tim Armstrong <tarmstr...@cloudera.com> Gerrit-Comment-Date: Thu, 24 May 2018 17:07:56 +0000 Gerrit-HasComments: No
