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From Paul Davis <paul.joseph.da...@gmail.com>
Subject Re: format of database sequence
Date Tue, 26 Oct 2010 19:23:32 GMT
On Tue, Oct 26, 2010 at 3:06 PM, Randall Leeds <randall.leeds@gmail.com> wrote:
> I don't see any way to avoid this and we've been talking about it for a while.
> +1
>
> On Tue, Oct 26, 2010 at 11:59, Adam Kocoloski <kocolosk@apache.org> wrote:
>> Hi all, I've been meaning to bring this up for a while.  CouchDB uses integer sequence
numbers in the _changes feed and update_seq values, but I don't see any sensible way to preserve
that interface in BigCouch.  The database sequence in BigCouch needs to combine the sequences
of several database shards; currently it's a string formatted like
>>
>> "1234-Base64Data"
>>
>> The first piece is the sum of the shard sequence numbers and is not actually used
by BigCouch.  The second piece is the actual data about the state of the cluster.  This
format causes a couple of issues:
>>
>> 1) the replicator occasionally sorts sequence numbers and when it does so, it sorts
the BigCouch ones lexicographically and concludes that e.g. "99-..." is the only checkpoint
it will ever need to store.
>>
>> 2) client libraries might not treat the sequence as an opaque data type and may break
when operating against a BigCouch.
>>
>> My personal preference would be to change the format of the Apache CouchDB sequence
to a string at the next major release.  Thoughts?
>>
>> Adam
>>
>>
>

Is there a possibility to retain a guarantee of triangle inequality
for update sequences? In my experience people are mostly using them to
detect an ordering. It seems like if we could give a loose ordering,
that'd be better than just an opaque type. Though, I'm also not sure
how that'd work in relation to string comparison operators in most
languages.

I'm +1 on the switch, I'm just wondering if we can do it without
making them completely opaque.

Paul Davis

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