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From Dirkjan Ochtman <dirk...@ochtman.nl>
Subject Re: Is reduce not incremental?
Date Sun, 19 Jun 2011 14:07:20 GMT
On Sun, Jun 19, 2011 at 10:10, Aroj George <arojis@gmail.com> wrote:
> Yes, the map step is not redone, but I thought the reduce values are cached
> in the internal non-leaf nodes?
> Why then does Couch rerun the reduce every time for the exact same query (
> same group level etc..)

AFAIK, the reduce results are cached in a tree-shaped cache on-disk,
where each member has the reduced results from all its child nodes. If
your query does not exactly match a single parent node, the reduce
query will have to skim a few parent nodes and reduce their results
further (i.e. with rereduce=True). This certainly doesn't mean that
each reduce query will have to calculate the full results from
reducing all the map results, though.

Cheers,

Dirkjan

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