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From Chris Anderson <>
Subject Re: M/R/M, again
Date Thu, 28 Jan 2010 00:00:23 GMT
On Wed, Jan 27, 2010 at 3:14 PM, Markus Jelsma <> wrote:
> Hello list and core developers,
> Some six months ago a thread emerged [1] concerning a possible
> map/reduce/merge in CouchDB. The question was if CouchDB would put this
> feature on its list of proposals (which it still isn't).
> Well, i now humbly attempt to get this topic back to the attention of the
> core developers and users that also feel a need for having such a feature
> on board.
> As far as i know M/R/M would be most helpful in returning related
> documents with just one key, instead of using sneaky techniques as
> described on the wiki [2] that allows us to fetch related documents but
> force us to retrieve two or more documents to do so.
> Instead of fetching two or more documents, i'd prefer to fetch just a
> single document queried with a `complex` key such as ["customer_id",
> "product_id"]. This would then return one document containing information
> on the customer as well as the number of products he/she ordered (we have
> a separate document for each purchase).
> Now we need to use the trick described but, i'm sure most of you would
> agree, it would be much easier to have a complete document with all
> required information instead of parsing an arbitrary number of documents
> as we must do now.
> To finish this message; i'd first like to apologize if i understood it all
> completely wrong, if so, please enlighten me and others for the sake of
> sharing clear information. Secondly, if it actually is a most beneficial
> feature for many of us, can we `vote` for it to be integrated in CouchDB
> instead of a possible contrib?

There are a number of ways things like this could be accomplished. One
I proposed recently is the facility to have CouchDB automatically copy
any  http view query result (local or remote) to a database full of
documents (one document for each row). This gives you a lot of
flexibility, but it is not incremental.

I think it's ok if it's not incremental. Hadoop is a batch process,
and people are fine with that.

The cool thing about this is it's in the HTTP domain so it will work
on a cluster, can be cached, etc.


> Any advanced insight is much appreciated.
> Cheers!
> [1]:
> [2]:

Chris Anderson

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