Re: Exposing the Xact commit order to the user

Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com> writes:
> Perhaps I'm missing something, but I thought that Slony currently uses a
> heartbeat, and all transactions committed between two beats are banged
> together and committed as one in the slave so that their relative commit
> order doesn't matter.

I guess Slony does the same as pgq here: all events of all those
transactions between two given ticks are batched together in the order
of the event commits. (In fact the batches are made at the consumer
request, so possibly spreading more than 2 ticks at a time).

If you skip that event ordering (within transactions), you can't
maintain foreign keys on the slaves, among other things.

The idea of this proposal is to be able to get this commit order
directly from where the information is maintained, rather than use some
sort of user sequence for that.

So even ordering the txid and txid_snapshots with respect to WAL commit
time (LSN) won't be the whole story, for any given transaction
containing more than one event we also need to have them in order. I
know Jan didn't forget about it so it must either be in the proposal or
easily derived, too tired to recheck.

Regards,
--
dim