On 10/02/2009, at 9:44 AM, Damien Katz wrote:
On Feb 9, 2009, at 5:59 PM, Antony Blakey wrote:
OK, I give up.
Given compaction and/or revision pruning (as Damien has proposed in
another thread), even generic 'Eventual Consistency' isn't
guaranteed.
Revision stemming is 100% optional, and the compaction works the
same as it did 0.8.0. I'm not sure why you think 'Eventual
Consistency' isn't guaranteed.
Because it depends on a steady state that may never be reached as long
as modification stays ahead of replication - the 'eventual' point
might be always ahead of the shared state.
Compaction and revision stemming (which is required to avoid unbounded
growth) make intermediate states inconsistent because they can delete
either the data of a document rev or the document rev itself. In the
face of compaction, it's possible for consistency to only be achieved
when the replication reaches the same MVCC commit point that the
compaction was operating against. Revision stemming has a similar
effect, although it has the further issue of being automatic i.e. not
scheduled.
That's ignoring replication failure, either temporary or permanent,
which further complicates the picture. Given that intermediate states
are not necessarily consistent, anything that leaves you in an
intermediate state without a way forward, repudiates the guarantee of
Eventual Consistency.
Antony Blakey
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