Structure of Erlang MR Arg

Jeremiah Peschka jeremiah.peschka at gmail.com
Thu Feb 14 10:58:41 EST 2013


Christian brought up something in the "ListKeys or MapReduce" thread that
deserves a discrete thread.

In the MapReduce Implementation docs [1], it looks like the Arg parameter
of an Erlang MR phase is not a single argument but is, in fact, a proplist
of Erlang terms, am I correct in assuming that this is the case?

And, if this is the case, would the JSON submitted to Riak look something
like this:

{"reduce":{"language":"erlang",
           "module":"riak_kv_mapreduce",
           "function":"reduce_count_inputs",
           "arg":{"do_prereduce":true,
                  "reduce_phase_batch_size": 250
                 }
           }
}

As we're mucking around in the lower levels of Corrugated Iron, I want to
make sure we're able to send the appropriate jibber jabber back to Erlang
phases.

[1]:
http://docs.basho.com/riak/latest/references/appendices/MapReduce-Implementation/

---
Jeremiah Peschka - Founder, Brent Ozar Unlimited
MCITP: SQL Server 2008, MVP
Cloudera Certified Developer for Apache Hadoop
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