Re: Sync Rep: First Thoughts on Code

On Sat, 2008-12-13 at 21:35 -0500, Robert Haas wrote:
> On Sat, Dec 13, 2008 at 1:29 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> > "Robert Haas" <robertmhaas(at)gmail(dot)com> writes:
> >> I think we need to reserve the term "synchronous replication" for a
> >> system where transactions that begin at the same time on the primary
> >> and standby see the same tuples. Clearly that is "more" synchronous
> >
> > We won't call it anything, because we never will or can implement that.
> > See the theory of relativity: the notion of exactly simultaneous events
>
> OK, fine. I'll be more precise. I think we need to reserve the term
> "synchronous replication" for a system where transactions that begin
> on the standby after the transactions has committed on the master see
> the effects of the committed transaction.
>

If it's guaranteed to be visible on the standby after it's committed on
the master, and you don't have any way to make it actually simultaneous,
then that implies that it's visible on the slave for some brief period
of time before it's committed on the master.

That situation is still asymmetric, so why is that a better use of the
term "synchronous"?

Regards,
Jeff Davis