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Subject: Re: Using _rev in application logic
From: Jan Lehnardt <jan@apache.org>
In-Reply-To: <t2y559193f01004010532rfa3783cerea997112c9450231@mail.gmail.com>
Date: Thu, 1 Apr 2010 15:42:40 +0200
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References: <t2y559193f01004010532rfa3783cerea997112c9450231@mail.gmail.com>
To: user@couchdb.apache.org

Hi Moritz,

On 1 Apr 2010, at 14:32, Moritz Post wrote:

> Hi CouchDB people
>=20
> I am currently playing with the couchdb and pretty impressed by =
several of
> the feature on offer. Great job so far. While reading up on various =
web
> resources i have come to conclude that it is discouraged to use the =
_rev
> field for application related logic since the revisions are removed =
when
> compacting and they are not replicated when using replication.
>=20
> Looking at my possible usecase however, i would very much like to use =
the
> _rev key to track changes in my document. So here are several =
questions
> regarding that topic:
>=20
> 1. Is it generally discouraged to use the _rev in application logic?

Yes, you should not rely on old revisions to be around in your app. Your
app will fail in unexpected ways and perceive data-loss if you rely on
revisions being around forever.

> 2. Is compacting something i would like to do for other reasons than =
to
> remove older revisions (so i could basically not do it)

CouchDB's b-tree store is sparse, unless you make very few very large =
bulk
doc inserts, you will waste a lot of space. Not running compaction is =
considered
"doing it wrong".


> 2. Is it possible to somehow also replicate the revision while =
replicating?

This is another reason for not using revisions in applications.


> 3. Is it good practice to use the _rev field in views?

Views can only always see the latest revision of a document. You can't =
even
access previous revisions.


> Any other clarifications in regards to _rev are also welcome.

We encourage this workflow:

1. Load a document,
2. make a copy,
3. change the document to reflect your changes,
4. attach the copy to the new changed document,
5. save back to CouchDB.


> Thanks in advance and keep up the good work

Welcome and thanks, keep the questions coming :)

Cheers
Jan
--