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From "John Vines (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (ACCUMULO-1568) Make configuration changes Atomic
Date Fri, 12 Jul 2013 17:31:49 GMT

    [ https://issues.apache.org/jira/browse/ACCUMULO-1568?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13707116#comment-13707116
] 

John Vines commented on ACCUMULO-1568:
--------------------------------------

I think zookeeper transactions are used for writes, not reads, but I could be mistaken. This
helps to mitigate this possibility, but I don't think it would prevent a client from having
a partial view.

However, if we're concerned about partial views, then this could more easily be accomplished
by changing the way we store the iterators in zookeeper, but that has it's own issues. If
we flatten all iterators and settings to a single znode we can guarantee everything is in
sync, but then there's the race condition in the read/modify/write, but that can be handled
by stat versions.
                
> Make configuration changes Atomic
> ---------------------------------
>
>                 Key: ACCUMULO-1568
>                 URL: https://issues.apache.org/jira/browse/ACCUMULO-1568
>             Project: Accumulo
>          Issue Type: Bug
>            Reporter: Keith Turner
>             Fix For: 1.6.0
>
>
> I have not seen this issue, but its something I thought of.  Assume the following happens.
>  * iterators I1 ... I10 are configured to Table T1 at time 1
>  * iterators NI1 ... NI10 are configured to Table T1 at time 2
>  * compaction is reading iterator config and reads I1 ... I5  and NI4 ... NI9, a combination
of the two iterator configurations w/o NI10, this could be really bad.
> Seems like this could be solved by use of Zookeeper transactions.   The Accumulo API
will need to change to allow setting many iterators or config settings at once.
>  
>  

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