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From "Michael Berman (JIRA)" <j...@apache.org>
Subject [jira] [Created] (ACCUMULO-2542) Add mechanism to cancel scans
Date Mon, 24 Mar 2014 21:00:56 GMT
Michael Berman created ACCUMULO-2542:
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             Summary: Add mechanism to cancel scans
                 Key: ACCUMULO-2542
                 URL: https://issues.apache.org/jira/browse/ACCUMULO-2542
             Project: Accumulo
          Issue Type: Improvement
          Components: tserver
            Reporter: Michael Berman


ScannerBase.close() closes all connections to a given scan, but if there's an iterator spinning
on the scan, it will keep running at least until a record makes it all the way out of the
iterator stack.  If you have a bug in an iterator, or a filter that doesn't match anything,
or a combiner that matches everything, then that could mean scanning an entire table.  It
would be nice if there were some mechanism to interrupt that process.

We probably couldn't do anything about a really buggy externally provided iterator that just
spins without calling next() downstream (short of calling Thread.close(), which is probably
a bad idea), but accumulo iterators could periodically check for cancellation and bail gracefully
(maybe each time we're about to load a new block?).  It would be nice to provide a mechanism
for external iterators to check their cancellation status so they can have an opportunity
to be well behaved if they're doing anything that might take a while, but that seems less
important.



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