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From "Todd Lipcon (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-2001) HDFS-1073: Kill previous.checkpoint, lastcheckpoint.tmp directories
Date Thu, 26 May 2011 07:47:47 GMT

    [ https://issues.apache.org/jira/browse/HDFS-2001?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13039568#comment-13039568

Todd Lipcon commented on HDFS-2001:

I let it loop for a while and it did somewhere around 150,000 distinct checkpoints coming
from two NNs (of a very small image). I think this is pretty stable / good to go.

> HDFS-1073: Kill previous.checkpoint, lastcheckpoint.tmp directories
> -------------------------------------------------------------------
>                 Key: HDFS-2001
>                 URL: https://issues.apache.org/jira/browse/HDFS-2001
>             Project: Hadoop HDFS
>          Issue Type: Sub-task
>          Components: name-node
>    Affects Versions: Edit log branch (HDFS-1073)
>            Reporter: Todd Lipcon
>            Assignee: Todd Lipcon
>             Fix For: Edit log branch (HDFS-1073)
>         Attachments: hdfs-2001.txt
> In the old design for edits/image storage, the secondary namenode does a complicated
dance of moving "current/" to "lastcheckpoint.tmp", checkpointing into "current/", then moving
"lastcheckpoint.tmp" back to "previous.checkpoint". The idea here was so that there would
always be one directory with a valid set of storage files.
> In the HDFS-1073 design, this complicated dance isn't necessary. If a checkpoint fails,
we can just rm that single fsimage_N.ckpt file and still be left with a valid storage directory.
> So, we can just let the 2NN keep a single current/ dir around for all checkpoints and
eliminate the complexity of the dance.

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