Re: 2-phase commit

Tom Lane wrote:
> Bruce Momjian <pgman@candle.pha.pa.us> writes:
> > Marc G. Fournier wrote:
> >>> Or the slave could reject the request.
> >> 
> >> Huh?  The slave has that option??  In what circumstance?
> 
> > I thought the slave could reject if someone local already had the row
> > locked.
> 
> All normal reasons for transaction failure are supposed to be checked
> for before the slave responds that it's ready to commit.  Otherwise it's
> supposed to say it can't commit.
> 
> Basically the weak spot of 2PC is that it assumes there are no possible
> reasons for failure after "ready to commit" is sent.  You can make that
> approximately true, with sufficient investment of resources, but it's
> definitely not a pleasant assumption.

Yep.  There is no full solution.  I think it is like running with fsync
off --- if the OS crashes, you have to clean up --- if you fail on a
2-phase commit, you have to clean up.  Multi-master will be the same.

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