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From "Aaron T. Myers (Commented) (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HADOOP-8212) Improve ActiveStandbyElector's behavior when session expires
Date Mon, 26 Mar 2012 06:46:32 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-8212?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13238144#comment-13238144
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Aaron T. Myers commented on HADOOP-8212:
----------------------------------------

Nice catch on that race condition, Todd. I also very much like the way you've improved the
tests for this. Just a few nits follow. +1 once these are addressed.

# Please put some blank lines between preventSessionReestablishmentForTests, allowSessionReestablishmentForTests,
and getZKSessionIdForTests.
# Seems a little strange to put the "Ignoring stale result from ..." log message in isStaleClient,
where no decisions are being made about ignoring anything.
# typo: "...and passes it back back along with..."
                
> Improve ActiveStandbyElector's behavior when session expires
> ------------------------------------------------------------
>
>                 Key: HADOOP-8212
>                 URL: https://issues.apache.org/jira/browse/HADOOP-8212
>             Project: Hadoop Common
>          Issue Type: Improvement
>    Affects Versions: 0.23.3, 0.24.0
>            Reporter: Todd Lipcon
>            Assignee: Todd Lipcon
>         Attachments: hadoop-8212.txt
>
>
> Currently when the ZK session expires, it results in a fatal error being sent to the
application callback. This is not the best behavior -- for example, in the case of HA, if
ZK goes down, we would like the current state to be maintained, rather than causing either
NN to abort. When the ZK clients are able to reconnect, they should sort out the correct leader
based on the normal locking schemes.

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