Re: 2-phase commit

Tom Lane writes:

> No.  The real problem with 2PC in my mind is that its failure modes
> occur *after* you have promised commit to one or more parties.  In
> multi-master, if you fail you know it before you have told the client
> his data is committed.

I have a book here which claims that the solution to the problems of
2-phase commit is 3-phase commit, which goes something like this:

coordinator        participant
-----------        -----------
INITIAL            INITIALprepare -->
WAIT<-- vote commit        READY
(all voted commit)prepare-to-commit -->
PRE-COMMIT<-- ready-to-commit        PRE-COMMITglobal-commit -->
COMMIT            COMMIT


If the coordinator fails and all participants are in state READY, they can
safely decide to abort after some timeout.  If some participant is already
in state PRE-COMMIT, it becomes the new coordinator and sends the
global-commit message.

Details are left as an exercise. :-)

-- 
Peter Eisentraut   peter_e@gmx.net