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From Sebastian Cohnen <sebastiancoh...@googlemail.com>
Subject Re: How Does CouchDB Generate _rev Strings
Date Tue, 05 Oct 2010 16:21:01 GMT
I partly explained this some time ago on this ML. I'll c&p it quickly and hope it helps

> 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 05.10.2010, at 04:19, Robert Sosinski wrote:

> Hello,
> 
> I just wanted to ask how CouchDB generates the string used for the
> _rev.  The first part (being the number) is pretty self explanatory.
> However, I have not yet figured out how the second part that looks
> like a MD5 digest is created.  Would it be possible to
> deterministically predict the _rev "digest" before saving the
> document?
> 
> Any clarification would help.
> 
> Thanks,
> 
> -Robert


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