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From "Zhe Zhang (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (HDFS-9079) Erasure coding: preallocate multiple generation stamps when creating striped blocks
Date Wed, 23 Sep 2015 23:00:06 GMT

     [ https://issues.apache.org/jira/browse/HDFS-9079?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Zhe Zhang updated HDFS-9079:
----------------------------
    Affects Version/s: HDFS-7285
               Status: Patch Available  (was: Open)

> Erasure coding: preallocate multiple generation stamps when creating striped blocks
> -----------------------------------------------------------------------------------
>
>                 Key: HDFS-9079
>                 URL: https://issues.apache.org/jira/browse/HDFS-9079
>             Project: Hadoop HDFS
>          Issue Type: Sub-task
>    Affects Versions: HDFS-7285
>            Reporter: Zhe Zhang
>            Assignee: Zhe Zhang
>
> 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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