[jira] [Created] (ACCUMULO-1152) Add more sanity checks to limit the damage of multiple assignment

["Keith Turner (JIRA)" <ji...@apache.org>]

Keith Turner created ACCUMULO-1152:
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             Summary: 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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