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Message-Id: <201701070727.v077RDbX017911@ip-10-146-233-104.ec2.internal>
Date: Sat, 7 Jan 2017 07:27:13 +0000
From: "Huaisi Xu (Code Review)" <gerrit@cloudera.org>
To: Matthew Jacobs <mj@cloudera.com>, impala-cr@cloudera.com,
        reviews@impala.incubator.apache.org
CC: Dan Hecht <dhecht@cloudera.com>, Tim Armstrong <tarmstrong@cloudera.com>
Reply-To: hxu@cloudera.com
Subject: =?UTF-8?Q?=5BImpala-ASF-CR=5D_IMPALA-4740=3A_Add_option_to_use_hdfsPread=28=29_for_HDFS_hedged_reads=0A?=
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archived-at: Sat, 07 Jan 2017 07:27:27 -0000

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?

I missed. it calls a different signature. hdfspread calls read(long position, byte[] buffer, int offset, int length). thanks for pointing it out..

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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