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Subject: Re: Control view query performance
From: Robert Samuel Newson <rnewson@apache.org>
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Date: Mon, 14 Jul 2014 12:16:24 +0100
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To: user@couchdb.apache.org


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 =
effects.

B.


On 14 Jul 2014, at 05:54, Stanley Iriele <siriele2x3@gmail.com> wrote:

> firstly..Thanks for the,I answer appreciate that. I was in a hurry =
while
> writing the past email
>=20
> 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.
>=20
> 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 so...is that a configurable thing?
>=20
>=20
> On Sun, Jul 13, 2014 at 9:33 PM, Jens Alfke <jens@couchbase.com> =
wrote:
>=20
>> I am no expert on the implementation of CouchDB, but I don=92t =
believe your
>> question makes sense in the form that you asked it. The changes feed =
isn=92t
>> related to views at all. Rather, there=92s an underlying by-sequence =
index in
>> the main database that=92s scanned to generate that feed. And it =
doesn=92t
>> =93calculate=94 docs; it just returns existing doc IDs and revision =
IDs.
>>=20
>> If that=92s not what you were actually asking, you=92ll need to =
rephrase your
>> question more clearly.
>>=20
>> =97Jens
>>=20
>> On Jul 13, 2014, at 8:49 PM, Stanley Iriele <siriele2x3@gmail.com> =
wrote:
>>=20
>>> any thoughts on this?...Its not a blocker..I'd just really like to =
know
>>>=20
>>>=20
>>> On Thu, Jul 10, 2014 at 3:44 PM, Stanley Iriele =
<siriele2x3@gmail.com>
>>> wrote:
>>>=20
>>>> 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.
>>>>=20
>>>> Lastly...is there a way to configure or control any of the settings =
that
>>>> would dictate the above?..like 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
>>>>=20
>>=20
>>=20