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From Paul Davis <paul.joseph.da...@gmail.com>
Subject Re: revisions and CouchDB as Temporal database
Date Thu, 19 Nov 2009 06:37:28 GMT
On Thu, Nov 19, 2009 at 1:12 AM, sftf <sftf-misc@mail.ru> wrote:
> Why we need to reinvent a revision mechanism at application level,
> instead of using existing built-in one?
> This built-in mechanism is very useful in applications that need
> to maintain revision history of documents (aka Temporal Database).
>
> But now compaction and replication treats older versions of each document as garbage,
> but not as document's history useful at the application level.
>
> So questions is:
> It may be useful to make this revision mechanism as the temporal feature (in sense of
transaction-time)
> of CouchDB?
>
> And for this:
> a) invent option to compact without removing old revisions from the database and
>   option to removing revisions older than the given timestamp
> b) invent replication option to replicate revisions too
> c) invent optional flexible timestamping of revisions
> Thanks.
>
>

While CouchDB's MVCC tokens may appear to be a replacement for
revision systems, they are fundamentally not qualified for such a
task. They are only a specific implementation of optimistic
concurrency and are far removed from content tracking as would be
required.

Attempting to attach a temporal meaning to the MVCC tokens is also a
fairly common reaction. This is generally born out of a misconception
of what these tokens are for. Specifically, MVCC tokens are explicitly
opaque. Applications are not allowed to depend on their format or
implementation defined meaning. Attempting to attach a time based
definition to these tokens violates many assumptions as to what they
represent.

HTH,
Paul Davis

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