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From "Keith Turner (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (ACCUMULO-1152) Add more sanity checks to limit the damage of multiple assignment
Date Tue, 05 Mar 2013 21:24:13 GMT

    [ https://issues.apache.org/jira/browse/ACCUMULO-1152?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13593929#comment-13593929
] 

Keith Turner commented on ACCUMULO-1152:
----------------------------------------

Just had a realization, before a walog can be used it must be written to the metadata table.
 So its likely the metadata table check will prevent a tserver from getting new logs.  But
this check is just based on cache.

If a tserver does see a metadata table write fail because it does not hold its lock, it should
probably do something.
                
> Add more sanity checks to limit the damage of multiple assignment
> -----------------------------------------------------------------
>
>                 Key: ACCUMULO-1152
>                 URL: https://issues.apache.org/jira/browse/ACCUMULO-1152
>             Project: Accumulo
>          Issue Type: Improvement
>            Reporter: Keith Turner
>             Fix For: 1.6.0
>
>
> When an issue like ACCUMULO-954 comes along and causes a tablet to be hosted on multiple
tablet servers, its nice to have sanity checks that limit the damage this can cause.
> Accumulo already has a sanity check on writes to the metadata table that ensures the
tablet server making the write still holds a lock.  This has reliably triggered in cases of
multiple assignment bugs.  It would be nice to have more checks like this.  Below are some
places I think checks would be useful, are there more?
>  * Tserver attempts to positively check it holds its lock before getting a new walog.
>  * Clients take some action to clear lockless tservers from their metadata table cache.
 This would help prevent writing data to a zombie tserver that may lose data, or reading stale
data from a zombie tserver.

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