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From Robert Newson <>
Subject Re: Map Reduce Implementation
Date Fri, 03 Aug 2012 18:27:04 GMT
Oops, this slipped by me earlier.

The engine isn't relevant, CouchDB supports pluggable view servers.

CouchDB currently builds a view group sequentially (though different view groups build concurrently),
but after the BigCouch merge this will change to be parallel (up the number of shards of your
database, which is configurable at database creation time).


On 3 Aug 2012, at 19:10, Jens Alfke wrote:

> On Aug 3, 2012, at 1:54 AM, Jan Fajerski <> wrote:
>> What Javascript engine is used,
> SpiderMonkey.
>> how is workload distributed (if at all) 
> I don't believe it is. Erlang itself is good at multiprocessing, but it runs SpiderMonkey
in a separate process. I don't know whether it spawns more than one of these processes. In
any case there is none of the fully-distributed mapping the way Google does it where map requests
get farmed out to multiple computers. CouchDB doesn't use M/R as a way to process ridiculously
large data sets, it uses it as a way to flexibly query semi-structured data.
> [Disclaimer: I'm not an expert on the implementation of CouchDB.]
>> May the dev list be a better place to ask such questions?
> Most likely, yes.
> —Jens

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