On 17/02/2009, at 9:26 AM, Robert Newson wrote:
The point of doing it in the server is that every node guarantees
Monotonic
Writes, and you never have to worry about failing because you can't
achieve
it. Given the current server implementation, IMO it's more likely
than not
that you would fail.
This comment leaves me puzzled which is entirely the fault of my poor,
tired brain.
More likely my poor explanation. Current CouchDB replication semantics
are very unfriendly to Monotonic Writes, because they only replicate
the data of the head revision (and conflict sources). Compaction makes
it theoretically worse by deleting data that wouldn't get replicated,
but I say theoretically because compaction is only a barrier to fixing
the problem - replication already acts as though constant compaction
was occurring. The proposed revision stemming does however make it
practically worse because all records of writes disappear from a
prefix of the document revisions, and such removal occurs at multiple
unaligned points in the linear write log. There's no equivalent to
Bayou's handling of log truncation.
I haven't described an alternative to the current multi-node proposal
(which isn't a formal proposal). My comments purely concern the
current implementation of single-node operation and replication.
Antony Blakey
-------------
CTO, Linkuistics Pty Ltd
Ph: 0438 840 787
He who would make his own liberty secure, must guard even his enemy
from repression.
-- Thomas Paine
