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From Robert Samuel Newson <>
Subject Re: Control view query performance
Date Mon, 14 Jul 2014 11:16:24 GMT

CouchDB manages a pool of couchjs processes, any one of which is capable of evaluating Javascript
map/reduce functions.

A single view group (all views in the same ddoc) is indexed serially using a single couchjs
process (aka, there is no parallelism here). In CouchDB 2.0, of course, a database can, and
typically does, consist of multiple shards, introducing parallelism to view builds among other


On 14 Jul 2014, at 05:54, Stanley Iriele <> wrote:

> firstly..Thanks for the,I answer appreciate that. I was in a hurry while
> writing the past email
> To be slightly clearer. I know that the _changes feed is generated from
> some bookkeeping mechanism internal to the database. When I said
> "Calculated for a particular set of entries" I mean the actual javascript
> view server that is evaluating your map function because the doc(s) have
> been fed to it and it must response with the emitted results. I ..could
> have phrased that better.
> My questions revolve around how CouchDB utilizes the view server...and if
> there is only one of them running at a given time on a box.The docs suggest
> that CouchDB talks to a view server with a line bases protocol, but I don't
> know there can be more than one view server executing map functions at a
> time...and if that a configurable thing?
> On Sun, Jul 13, 2014 at 9:33 PM, Jens Alfke <> wrote:
>> I am no expert on the implementation of CouchDB, but I don’t believe your
>> question makes sense in the form that you asked it. The changes feed isn’t
>> related to views at all. Rather, there’s an underlying by-sequence index in
>> the main database that’s scanned to generate that feed. And it doesn’t
>> “calculate” docs; it just returns existing doc IDs and revision IDs.
>> If that’s not what you were actually asking, you’ll need to rephrase your
>> question more clearly.
>> —Jens
>> On Jul 13, 2014, at 8:49 PM, Stanley Iriele <> wrote:
>>> any thoughts on this?...Its not a blocker..I'd just really like to know
>>> On Thu, Jul 10, 2014 at 3:44 PM, Stanley Iriele <>
>>> wrote:
>>>> When a doc needs to be calculated for a particular set of entries from
>> the
>>>> changes feed...are docs sent one at a time or in batches?... And is
>> there
>>>> just one view server doing all of the computation.
>>>> there a way to configure or control any of the settings that
>>>> would dictate the above? number of view servers.. Or batch size
>> for
>>>> docs.... Etc... And if not should there be?.. But I've been very curious
>>>> about this for a while... I looked a few view server implementations..
>>>> But...meh

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