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From "Ayende Rahien" <aye...@ayende.com>
Subject Re: Newbie questions
Date Wed, 24 Sep 2008 07:53:23 GMT
On Wed, Sep 24, 2008 at 10:46 AM, Jan Lehnardt <jan@apache.org> wrote:

>
>  Anyway, I had a few questions that I hope I'll be able to get some answers
>> for.
>> merge conflicts - how does couch db decides on "best" revision?
>>
>
> It arbitrarily choses one revision. The only guarantee that is made is that
> for
> the same conflict all nodes in a CouchDB cluster choose the same latest
> revision to ensure data consistency.
>

How do you ensure that across a cluster, all nodes will select the same
version?
Assume that I have the following sequence of events:
- create doc A (v1)
- update doc A from V1 (v2)
- update doc A from v1 (v3) - conflict
- update doc A from v1 on separate machine (v?) - conflict


How does it get resolved?


> to get from the code so far are:
>> - How is the data stored? I think that it is a binary tree on disk, but I
>> am
>> not following how updates to that can be safe to do so with ACID
>> guarantees.
>>
> Two questions that are of particular interest to me, and I haven't been
> able
>
> Writes are serialized. Only one write can happen at a time and it is
> completely
> flushed and committed to disk (2 x fsync()) before another write comes in.
> Writes
> are append-only. No data is ever overwritten. This gives us the ACID & MVCC
> buzzcronyms :-)
>

Can you speak more on the actual file format? I don't think that I
understand how you can have append only with binary trees.

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