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From "Todd Lipcon (Commented) (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-2693) Synchronization issues around state transition
Date Tue, 20 Dec 2011 03:17:31 GMT

    [ https://issues.apache.org/jira/browse/HDFS-2693?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13172886#comment-13172886
] 

Todd Lipcon commented on HDFS-2693:
-----------------------------------

Found a nasty bug in the current patch: in {{getBlockLocationsUpdateTimes}} the {{checkOperation}}
call has to move down inside {{try..catch}} or else calling this function on an NN in standby
state will leak the FSN readlock, killing the SBN. I'll upload a new patch soon. Still worth
reviewing the general patch since most of it seems to be working correctly.
                
> Synchronization issues around state transition
> ----------------------------------------------
>
>                 Key: HDFS-2693
>                 URL: https://issues.apache.org/jira/browse/HDFS-2693
>             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-2693.txt
>
>
> Currently when the NN changes state, it does so without synchronization. In particular,
the state transition function does:
> (1) leave old state
> (2) change state variable
> (3) enter new state
> This means that the NN is marked as "active" before it has actually transitioned to active
mode and opened its edit logs. This gives a window where write transactions can come in and
the {{checkOperation}} allows them, but then they fail because the edit log is not yet opened.

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