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 INITIAL
prepare -->
WAIT
<-- vote commit
READY
(all voted commit)
prepare-to-commit -->
PRE-COMMIT
<-- ready-to-commit
PRE-COMMIT
global-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(at)gmx(dot)net