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From Chris Anderson <jch...@apache.org>
Subject Re: svn commit: r815984 - in /couchdb/trunk: share/www/script/test/view_include_docs.js src/couchdb/couch_httpd_db.erl src/couchdb/couch_httpd_view.erl
Date Thu, 17 Sep 2009 22:51:55 GMT
On Thu, Sep 17, 2009 at 3:45 PM, Delta 2038 <delta2038@gmail.com> wrote:
> On Wed, Sep 16, 2009 at 6:42 PM, Chris Anderson <jchris@apache.org> wrote:
>
>> Of course, the usual include_docs performance caveats apply, but this
>> time we get a feature out of it!
>>
>
> A bit off-topic here, but would you elaborate maybe just a little bit the
> include_docs performance caveats? I assume that it involves reading another
> view to grab the documents since they are not present in the current view?
> We are interested in learning how much of a performance hit it actually
> incurs. We could set up some load tests ourselves to find out, but if you
> already have some pretty good idea... :)
>

Include docs, whether fetching a specified doc, or just the doc that
emitted the row, has a per-row cost of pulling documents from the
database. So it could incur additional disk seeks - this shouldn't
matter unless you are just on the edge of being able to handle the
load you are experiencing.

Generally, views are awesome because they can be streamed from disk
with a minimum of seeks. Include docs doesn't have this bit of
awesome. I'm not sure what numbers you'd see, but it would probably
depend a lot on hardware, load, and configuration (putting views on
their own spindle could help mitigate this a fair amount.)



-- 
Chris Anderson
http://jchrisa.net
http://couch.io

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