You can return arrays and objects, whatever json allows. But if the
object keeps getting bigger the more rows it reduces, then it simply
won't work.
The exception is that the size of the reduce value can be logarithmic
with respect to the rows. The simplest example of logarithmic growth
is the summing of a row value. With Erlangs bignums, the size on disk
is Log2(Sum(Rows)), which is perfectly acceptable growth.
-Damien
On Aug 19, 2008, at 8:14 PM, Nicholas Retallack wrote:
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 <[EMAIL PROTECTED]>
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. http://www.slicehost.com/
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.
