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From "Todd Lipcon (Commented) (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-2794) HA: Active NN may purge edit log files before standby NN has a chance to read them
Date Mon, 06 Feb 2012 21:08:59 GMT

    [ https://issues.apache.org/jira/browse/HDFS-2794?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13201584#comment-13201584
] 

Todd Lipcon commented on HDFS-2794:
-----------------------------------

Changed the description to:
{quote}
  <description>The number of extra transactions which should be retained
  beyond what is minimally necessary for a NN restart. This can be useful for
  audit purposes or for an HA setup where a remote Standby Node may have
  been offline for some time and need to have a longer backlog of retained
  edits in order to start again.
  Typically each edit is on the order of a few hundred bytes, so the default
  of 1 million edits should be on the order of hundreds of MBs or low GBs.
{quote}
Sound good?
                
> HA: Active NN may purge edit log files before standby NN has a chance to read them
> ----------------------------------------------------------------------------------
>
>                 Key: HDFS-2794
>                 URL: https://issues.apache.org/jira/browse/HDFS-2794
>             Project: Hadoop HDFS
>          Issue Type: Sub-task
>          Components: ha, name-node
>    Affects Versions: HA branch (HDFS-1623)
>            Reporter: Aaron T. Myers
>            Assignee: Todd Lipcon
>         Attachments: hdfs-2794.txt
>
>
> Given that the active NN is solely responsible for purging finalized edit log segments,
and given that the active NN has no way of knowing when the standby reads edit logs, it's
 possible that the standby NN could fail to read all edits it needs before the active purges
the files.

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