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From "Andrew Wang (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-6581) Write to single replica in memory
Date Fri, 19 Sep 2014 09:31:35 GMT

    [ https://issues.apache.org/jira/browse/HDFS-6581?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14140238#comment-14140238
] 

Andrew Wang commented on HDFS-6581:
-----------------------------------

I'd like to also echo Colin's desire to see some positive benchmark numbers before merging
this. Since the point of this JIRA is to improve read/write performance, it really seems like
we should verify that some nice gains are possible before adding this complexity. This is
what we did for HDFS-4949, and I did also ask for benchmarks in my comment about a month ago.

Arpit, I seem to remember you had a WIP short-circuit writes patch you were working on a while
ago. Do you have any numbers from that even? Colin wrote a vectorized sum microbenchmark using
zero-copy reads at HDFS-6287 you might be able to adapt. This does dredge up the discussion
about the design of short-circuit writes, but maybe that's a bridge that has to be crossed.

> Write to single replica in memory
> ---------------------------------
>
>                 Key: HDFS-6581
>                 URL: https://issues.apache.org/jira/browse/HDFS-6581
>             Project: Hadoop HDFS
>          Issue Type: Bug
>          Components: datanode
>            Reporter: Arpit Agarwal
>            Assignee: Arpit Agarwal
>         Attachments: HDFS-6581.merge.01.patch, HDFS-6581.merge.02.patch, HDFS-6581.merge.03.patch,
HDFS-6581.merge.04.patch, HDFS-6581.merge.05.patch, HDFS-6581.merge.06.patch, HDFSWriteableReplicasInMemory.pdf,
Test-Plan-for-HDFS-6581-Memory-Storage.pdf
>
>
> Per discussion with the community on HDFS-5851, we will implement writing to a single
replica in DN memory via DataTransferProtocol.
> This avoids some of the issues with short-circuit writes, which we can revisit at a later
time.



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