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Last active December 11, 2015 23:29
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Riak's MapReduce functionality cannot survive a node failure. If a vnode involved with a query fails while actively processing the request, the entire query will have to be re-run. The failed query should be automatically terminated, but you'll have to re-run the query yourself.
If you create queries using Riak Pipe (the technology layer beneath MapReduce), it is possible to create queries that can survive a vnode failure, but that is not a trivial exercise.
Regarding the empty result set you're seeing: one possibility is that a vnode has failed recently and has come back online without data. MapReduce will not currently trigger a read repair, but that problem should be resolved with the forthcoming Riak 1.3 release.
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