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From "Michael Berman (JIRA)" <>
Subject [jira] [Resolved] (ACCUMULO-2542) Add mechanism to cancel scans
Date Tue, 01 Apr 2014 21:43:15 GMT


Michael Berman resolved ACCUMULO-2542.

    Resolution: Implemented

Thanks [~kturner], you're right, looks like this already works fine.  Not sure what was wrong
with our original experiment, but I can't reproduce it now.

> Add mechanism to cancel scans
> -----------------------------
>                 Key: ACCUMULO-2542
>                 URL:
>             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

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