On Mar 3, 2009, at 6:00 PM, Chris Anderson wrote:
On Tue, Mar 3, 2009 at 6:52 AM, Wout Mertens <[email protected]>
wrote:
Since this question has been posed more than once, maybe main.js
should
have a uniq() function as well?
Dragons dragons...
This is one pattern Couch does not support (and it is not unique in
this way).
[...]
It's just taking a tall list and making it into a wide list. The
disadvantage of a wide list is that you have to have the whole thing
in memory at once. This is where Couch breaks down, because the
spidermonkey process eventually has to have all the unique rows of the
map in memory all at once.
Ok I understand, if your value grows for each reduce, you end up with
a huge value at the last reduce.
However, suppose you keep tags about documents in separate documents,
you would need uniq() to find out which tags a certain document has,
no? On the last re-reduce, would the total reduce value size not be at
most a few times the total amount of tags? So still manageable?
Would the problem be alleviated if you could specify for views that
couch should not reduce past the group level? In other words, only
calculate what's needed for views with group=true?
So I suppose that for now, this behavior should not be encouraged by
providing a uniq() function :-)
Wout.
