Commit/acknowledgment phase in CAS?

[ibrahim El-sanosi <ib...@gmail.com>]

Hi folks,


To achieve linearizable consistency in Cassandra, there are four
round-trips must be performed:

1.       Prepare/promise

2.       Read/result

3.       Propose/accept

*4.       **Commit/acknowledgment *



In the last phase in Paxos protocol (white paper), there is decide phase
only, no Commit/acknowledgment. DESIDE means to tell learners to apply the
accepted value.

If Commit/acknowledgment phase in CAS has similar purpose as DECIDE, then
why we have an acknowledgment round?


In fact, I want to know the purpose of Commit/acknowledgment phase in
lineazaible consistency in Cassandra. I have read the
http://www.datastax.com/dev/blog/lightweight-transactions-in-cassandra-2-0,
but it does not explain whole the picture.



I look forward to hearing from you

Ibrahim