Re: 2-phase commit

Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)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.

regards, tom lane