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From "Walter Su (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HADOOP-12047) Indicate preference not to affect input buffers during coding in erasure coder
Date Mon, 02 Nov 2015 02:23:27 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-12047?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14984642#comment-14984642

Walter Su commented on HADOOP-12047:

Thanks [~drankye] for updating. The latest patch LGTM. +1.

> Indicate preference not to affect input buffers during coding in erasure coder
> ------------------------------------------------------------------------------
>                 Key: HADOOP-12047
>                 URL: https://issues.apache.org/jira/browse/HADOOP-12047
>             Project: Hadoop Common
>          Issue Type: Sub-task
>            Reporter: Kai Zheng
>            Assignee: Kai Zheng
>             Fix For: HDFS-7285
>         Attachments: HADOOP-12047-HDFS-7285-v1.patch, HADOOP-12047-v2.patch, HADOOP-12047-v3.patch,
HADOOP-12047-v4.patch, HADOOP-12047-v5.patch, initial-poc.patch
> It's good to define and ensure input buffers are not affected during coding process in
raw erasure coders. Below are copied from discussion with [~jingzhao] in HDFS-8481:
> bq. In that case we cannot reuse the source buffers I guess? Then do we need to expose
this information in the decoder?
> bq. Good catch Jing! Yes in this case we can't reuse the source buffers here as they
need to be passed to caller/applications without being changed. I'm planning to re-implement
the Java coders in HADOOP-12041 and related, when done it's possible to ensure the input buffers
not to be affected. Benefits of doing this in coder layer: 1) a more clear contract between
coder and caller in more general sense for the inputs; 2) concrete coder may have specific
tweak to optimize in the aspect, ideally no input data copying at all, worst, make the copy,
but all transparent to callers; 3) allow new coders (LRC, HH) to be layered on other primitive
coders (RS, XOR) more easily.

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