On 09/02/2009, at 4:01 PM, Adam Kocoloski wrote:
Ok, thanks for the clarification. I don't see any major downsides
beyond the ones you already mentioned. The inability to replicate
between versions is a bit of a bummer -- I'd want to at least look
into a bridge that lets old servers replicate to new ones.
Your point about reducing the chance of collision is a good one,
especially since Couch is using a 32 bit sample space for revision
IDs. The probability of zero collisions between any two revisions
in a given document history is
N!/((N-M)! * N^M)
with N = 2**32 and M = "max rev history". With M = 128, that
probability drops to 0.999998. In a 400k document DB where each doc
has the max number of revisions it's likely that at least one has a
duplicate rev. That's no good. I think we could eventually see
transient cases of revisions being skipped by the replicator with
the trunk code.
If the revision were an SHA hash (admittedly), wouldn't the increased
value space, AND the fact that identical rev == identical document,
greatly relieve this problem?
Antony Blakey
--------------------------
CTO, Linkuistics Pty Ltd
Ph: 0438 840 787
The trouble with the world is that the stupid are cocksure and the
intelligent are full of doubt.
-- Bertrand Russell
