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From "Todd Lipcon (Updated) (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (HDFS-2874) HA: edit log should log to shared dirs before local dirs
Date Thu, 02 Feb 2012 00:11:53 GMT

     [ https://issues.apache.org/jira/browse/HDFS-2874?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Todd Lipcon updated HDFS-2874:
------------------------------

    Attachment: hdfs-2874.txt

Attached patch fixes this issue so long as the shared dirs are marked "required". The shared/non-shared
distinction doesn't make it down into JournalSet, so went with the required/non-required distinction,
which I think makes sense anyway. Once we implement HDFS-2769, we'll ensure that shared dirs
are always required.
                
> HA: edit log should log to shared dirs before local dirs
> --------------------------------------------------------
>
>                 Key: HDFS-2874
>                 URL: https://issues.apache.org/jira/browse/HDFS-2874
>             Project: Hadoop HDFS
>          Issue Type: Sub-task
>          Components: ha, name-node
>    Affects Versions: HA branch (HDFS-1623)
>            Reporter: Todd Lipcon
>            Assignee: Todd Lipcon
>            Priority: Critical
>         Attachments: hdfs-2874.txt
>
>
> Currently, the NN logs its edits to each of its edits directories in sequence. This can
produce the following bad sequence:
> - NN accumulates 100 edits (tx 1-100) in the buffer. Writes and syncs to local drive,
then crashes
> - Failover occurs. SBN takes over at txid=1, since txid 1 never got writen.
> - First NN restarts. It reads up to txid 100 from its local directories. It is now "ahead"
of the active NN with inconsistent state.
> The solution is to write to the shared edits dir, and sync that, before writing to any
local drives.

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