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From: Ido Ran <ido.ran@gmail.com>
Date: Sun, 12 Sep 2010 15:24:25 +0200
Message-ID: <AANLkTin8UrJbrQM3g4q=PvKQDiXzTugC_=Nk81e8YPLv@mail.gmail.com>
Subject: Re: Revsion Explained
To: user@couchdb.apache.org
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Thank you for the answer.

I though it is possible to compare two _rev fields of two documents and
based on the hash part (not the integer) to tell if they have the same
content. I guess it is not possible.

Ido

On Sun, Sep 12, 2010 at 3:14 PM, Sebastian Cohnen <
sebastiancohnen@googlemail.com> wrote:

> Hi Ido,
>
> consider the _rev token as an opaque value necessary for the mvcc (I'd call
> it mvcc-token, since "revision" is often misunderstood). The hash algorithm
> may even change someday. AFAIK it contains the document itself and also its
> history (at least parts of it). The algorithm ensures that the same document
> with the same history result in the same _rev token even on two different
> nodes. This behavior is required for conflict detection/resolution.
>
> Best
>
> Sebastian
>
>
> On 12.09.2010, at 14:43, Ido Ran wrote:
>
> > Hi,
> > I've read that the _rev fiel in each document is composed of two parts -
> > integer which increment by 1 on each change and MD5 hash of the JSON of
> the
> > document.
> > What part of the JSON is included in that hash?
> >
> > I've created a new document with _id of "foo" and single field name
> "start"
> > with value "99". I've save the document and it got _rev of
> > "1-b563730fcffb6583ff48980c1533e439".
> > I didn't change anything, just hit save again in Futon and not the _rev
> is
> > "2-75a41bb3bc74cb4d768466efa2a0c1ca".
> > If I hit save again I get another hash.
> >
> > Why is that?
> >
> > Thank you,
> > Ido
>
>

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