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From "Nicholas Retallack" <>
Subject Re: Reduce is Really Slow!
Date Wed, 20 Aug 2008 00:14:36 GMT
Oh!  I didn't realize that was a rule.  I had used 'return values' in
attempt to run the simplest test possible on my data.  But hey, values is an
array.  Does that mean you're not allowed to return objects like arrays from
reduce at all?  Because I was kind of hoping I could.  I was able to do it
with smaller amounts of data, after all.  Perhaps this is due to re-reduce
kicking in?

For the record, couchdb is still working on this query I started hours ago,
and chewing up all my cpu.  I am going to have to kill it so I can get some
work done.

On Tue, Aug 19, 2008 at 4:21 PM, Damien Katz <> wrote:

> I think the problem with your reduce is that it looks like its not actually
> reducing to a single value, but instead using reduce for grouping data. That
> will cause severe performance problems.
> For reduce to work properly, you should end up with a fixed size data
> structure regardless of the number of values being reduced (not stricty
> true, but that's the general rule).
> -Damien
> On Aug 19, 2008, at 6:55 PM, Nicholas Retallack wrote:
>  Okay, I got it built on gentoo instead, but I'm still having performance
>> issues with reduce.
>> Erlang (BEAM) emulator version 5.6.3 [source] [64-bit] [async-threads:0]
>> couchdb - Apache CouchDB 0.8.1-incubating
>> Here's a query I tried to do:
>> I freshly imported about 191MB of data in 155399 documents.  29090 are not
>> discarded by map.  Map produces one row with 5 fields for each of these
>> documents.  After grouping, each group should have four rows.  Reduce is a
>> simple function(keys,values){return values}.
>> Here's the query call:
>> time curl -X GET '
>> http://localhost:5984/clickfund/_view/offers/index?count=1&group=true&group_level=1
>> '
>> This is running on a 512MB slicehost account.
>> I'd love to give you this command's execution time, since I ran it last
>> night before I went to bed, but it must have taken over an hour because my
>> laptop went to sleep and severed the connection.  Trying it again.
>> Considering it's blazing fast without the reduce function, I can only
>> assume
>> what's taking all this time is overhead setting up and tearing down the
>> simple function(keys,values){return values}.
>> I can give you guys the python source to set up this database so you can
>> try
>> it yourself if you like.

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