Re: Two-phase commit

Tom Lane wrote:
> Oliver Jowett <oliver@opencloud.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