Re: Two-phase commit

Tom Lane wrote:
> Oliver Jowett <oliver(at)opencloud(dot)com> writes:
>
>>>At the API level, I like the PREPARE/COMMIT/ROLLBACK statements, but I
>>>think you have missed a bet in that it needs to be possible to issue
>>>"COMMIT PREPARED gid" for the same gid several times without error.
>
>
>>Isn't this usually where the GTM would issue "recover" requests to
>>determine the state of the individual resources involved in the global
>>transaction, and then only commit/abort the resources that need it? (I
>>think the equivalent in Heikki's work is a SELECT of the
>>pg_prepared_xact view)
>
>
> Well, the question is how long must the individual databases retain
> state with which to answer "recover" requests. I don't like "forever",
> so I'm proposing that there should be an explicit command to say "you
> can forget about this gid".

As I understand it, you don't need to keep state for committed txns,
it's only the prepared-but-not-yet-resolved txns that you have to
respond to a recover request with.

Then it seems like we already have a "forget about this GID" command for
prepared transactions: ROLLBACK PREPARED.

Probably the next question is, do we want a database-side timeout on how
long prepared txns can stay alive before being summarily rolled back?

-O