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From "Huaisi Xu (Code Review)" <ger...@cloudera.org>
Subject [Impala-ASF-CR] IMPALA-4740: Add option to use hdfsPread() for HDFS hedged reads
Date Sat, 07 Jan 2017 07:18:09 GMT
Huaisi Xu has posted comments on this change.

Change subject: IMPALA-4740: Add option to use hdfsPread() for HDFS hedged reads
......................................................................


Patch Set 2:

> The HDFS-5776 JIRA mentions that it's implemented for the pread()
 > code path, but it's not that clear. If you look at the code it's
 > very clear that it only kicks in on the pread() code path:
 > 
 > https://github.com/apache/hadoop/search?utf8=%E2%9C%93&q=isHedgedReadsEnabled

I may be wrong again (as always), hdfspread is not pread. from https://github.com/apache/hadoop/blob/f67237cbe7bc48a1b9088e990800b37529f1db2a/hadoop-hdfs-project/hadoop-hdfs-native-client/src/main/native/libhdfs/hdfs.c#L1426,
you can see hdfspread() invokes read(), and hdfsread() calls read() as well, and in turn read()
calls pread() as you can see in the link you just quoted. So this new gflag is essentially
ignored? What did I miss here?

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Gerrit-MessageType: comment
Gerrit-Change-Id: Iecc8b12aa20cbfe08f4ef6a08a191e49709d9525
Gerrit-PatchSet: 2
Gerrit-Project: Impala-ASF
Gerrit-Branch: master
Gerrit-Owner: Matthew Jacobs <mj@cloudera.com>
Gerrit-Reviewer: Dan Hecht <dhecht@cloudera.com>
Gerrit-Reviewer: Huaisi Xu <hxu@cloudera.com>
Gerrit-Reviewer: Internal Jenkins
Gerrit-Reviewer: Matthew Jacobs <mj@cloudera.com>
Gerrit-Reviewer: Tim Armstrong <tarmstrong@cloudera.com>
Gerrit-HasComments: No

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