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From Jarrod Roberson <>
Subject Re: Question About Top Tags Reduce Function
Date Tue, 25 May 2010 20:17:51 GMT
On Mon, May 24, 2010 at 5:19 PM, James Hayton <>wrote:

> Hi Everyone-
> ... CouchDB is pretty simple imho for the most
> part, but I haven't always been able to grasp the reduce functions and what
> I can and can't do.  ...

the gist of what a reduce function should and should not do is simple.
It should reduce a set of data down to a much smaller set of data.
In your case, thousands of tags down to a single entry with a total.
then in the rereduce part it might reduce those intermediate results even
So that many values or keys get reduced down to a very small percentage of
the original set.
And the high water mark filter also catches when you reduce down to 1 value
that is really big, as it checks the byte size of the reduced value. That is
why you can't take a thousand entries from values and reduce them to a
single value with all thousand things appended together, it will complain
about that.

Jarrod Roberson

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