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From Chris Anderson <>
Subject Re: sort by reduce value
Date Thu, 13 Aug 2009 20:14:36 GMT
On Wed, Aug 12, 2009 at 11:40 PM, Brian Candler<> wrote:
> On Mon, Aug 10, 2009 at 01:56:49PM -0700, Chris Anderson wrote:
>> The reason why CouchDB can't do the sorting by value inside itself is
>> that on a multi node cluster, an individual couch can't know the
>> global ordering. We have a commitment to ensuring that CouchDB's API
>> remains invariant regardless of the size of the underlying cluster.
>> So you basically have to copy the cluster-wide reduce values to an
>> intermediate storage mechanism (which itself can be a cluster) before
>> you can sort them by value.
> Not sure I understand. If this is a sharded cluster, then each node could
> sort its own subset of results; then it's very simple and efficient to merge
> the already-sorted results together.


Except that in order to get a global ordering for group reduces, you
have to do the ordering after the merge, not before.

Chris Anderson

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