{error, notfound} items in mapreduce during ownership handoff

Jeremy Raymond jeraymond at gmail.com
Thu Feb 28 11:28:34 EST 2013

Yesterday I added a new node to my cluster. During the time when ownership
handoff was happening (several hours of work) mapreduce map functions were
receiving {error, notfound} as inputs. My Erlang mapred functions weren't
designed to handle this. They hadn't encountered this before during normal
operation. After the ownership handoff process completed the {error,
notfound} inputs have stopped.

Any explanations for the {error, notfound} inputs during ownership handoff?
Is this because a node is attempting to process an object now moved to
another node? If this is the case would the notfound object be found on the
other node in the same mapreduce job (i.e. still visible to the overall
mapred process)? Should I assume {error, notfound} inputs for all mapred
jobs as a valid possible input and always handle it?

I've also accumulated about 50MB of "Pipe worker startup failed:fitting was
gone before startup" on each node during the ownership_transfer process.
These messages are benign?

Thanks a lot.

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