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From "Mike Drob (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (ACCUMULO-2140) Race conditions between client operations and upgrade
Date Fri, 17 Jan 2014 19:26:27 GMT

    [ https://issues.apache.org/jira/browse/ACCUMULO-2140?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13875150#comment-13875150
] 

Mike Drob commented on ACCUMULO-2140:
-------------------------------------

Do we intend to support live upgrades? I'd be happy with a documentation note for the upgrade
instructing people to stop all clients.

> Race conditions between client operations and upgrade
> -----------------------------------------------------
>
>                 Key: ACCUMULO-2140
>                 URL: https://issues.apache.org/jira/browse/ACCUMULO-2140
>             Project: Accumulo
>          Issue Type: Bug
>            Reporter: Christopher Tubbs
>            Assignee: Christopher Tubbs
>            Priority: Blocker
>             Fix For: 1.6.0
>
>
> While the master is upgrading, it also has a thread that is responding to client requests.
Since the upgrade renames tables and puts them in namespaces, there is a short period of time
where table existence checks that rely on the new zookeeper schema for tables are failing
to provide the correct answer.
> Example: when the tracer starts, it tries to create a "trace" table, if it doesn't exist.
The existence check returns false, so it creates a new trace table in the default namespace,
even though there exists an old one that has not yet been moved into the default namespace
during the upgrade. This results in two tables with the same name.
> An easy solution would be to fail to respond to client requests until after the upgrade
is complete. (eg. wait to start up the MasterClientServiceHandler thread).



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