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From "Tsz Wo Nicholas Sze (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-9079) Erasure coding: preallocate multiple generation stamps and serialize updates from data streamers
Date Fri, 23 Oct 2015 01:28:27 GMT

    [ https://issues.apache.org/jira/browse/HDFS-9079?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14970254#comment-14970254
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Tsz Wo Nicholas Sze commented on HDFS-9079:
-------------------------------------------

> ... => 2) Asks NN for new GS => 3) Gets new GS from NN => ...

What is the difference between #2 and #3?  Is it just a single RPC?

> ... For each new striped block group we can reserve NUM_PARITY_BLOCKS GS's. ...

Do you mean that client may update GS without letting NN knowing it?

> ... Then steps 1~3 in the above sequence can be saved. ...

How to save step #1?

> Erasure coding: preallocate multiple generation stamps and serialize updates from data
streamers
> ------------------------------------------------------------------------------------------------
>
>                 Key: HDFS-9079
>                 URL: https://issues.apache.org/jira/browse/HDFS-9079
>             Project: Hadoop HDFS
>          Issue Type: Sub-task
>          Components: erasure-coding
>    Affects Versions: HDFS-7285
>            Reporter: Zhe Zhang
>            Assignee: Zhe Zhang
>         Attachments: HDFS-9079-HDFS-7285.00.patch, HDFS-9079.01.patch, HDFS-9079.02.patch,
HDFS-9079.03.patch, HDFS-9079.04.patch, HDFS-9079.05.patch
>
>
> A non-striped DataStreamer goes through the following steps in error handling:
> {code}
> 1) Finds error => 2) Asks NN for new GS => 3) Gets new GS from NN => 4) Applies
new GS to DN (createBlockOutputStream) => 5) Ack from DN => 6) Updates block on NN
> {code}
> To simplify the above we can preallocate GS when NN creates a new striped block group
({{FSN#createNewBlock}}). For each new striped block group we can reserve {{NUM_PARITY_BLOCKS}}
GS's. Then steps 1~3 in the above sequence can be saved. If more than {{NUM_PARITY_BLOCKS}}
errors have happened we shouldn't try to further recover anyway.



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