Re: PITR for replication?

> Greg Stark
> "J. Andrew Rogers" <jrogers(at)neopolitan(dot)com> writes:
>
> > I may be completely missing the point here, but it looks to
> me as though
> > the PITR archival mechanism is also most of a native replication
> > facility. Is there anyone reason this couldn't be extended to
> > replication, and if so, is anyone planning on using it as such?
> >
> > My memory is fuzzy on this point, but I seem to recall that this is
> > (was?) how replication is more-or-less done for many of the big
> > commercial RDBMS.

You're right...it is the basis of a log shipping replication facility.
I'm keen no to get too far ahead of ourselves. Let's eat the mammoth one
bite at a time....or one patch at a time.

> Well "replication" is one of those things that means
> different things to
> different people. IMHO, this is one of the simpler, more
> reliable, mechanisms
> and would be nice to have. And you're right that it shouldn't
> require much
> more work, in fact it's probably easier than a lot of other
> cases that PITR
> requires.

I agree. PITR is intended initially as a recovery mechanism. Replication
has other purposes as well, such as locating data close to where it is
required (in master-multi-slave replication scenarios), which is
certainly not an objective or even a likely end point of the PITR work.
The PostgreSQL community is lucky enough to have some very competent
people working on those other approaches and I would recommend everybody
checks out that work.

> For a long time Oracle has supported this mechanism for
> running warm standby
> databases. Basically you maintain a second database and every
> time an archived
> log is finished you ship it over and immediately "restore" it
> on the standby
> machine. Whenever you have a failure you can quickly fail
> over to the standby
> database which is all ready to go and up-to-date within
> minutes of your
> failure.

This facility is one of the intended features, if all goes well. But it
is an advanced feature, not the bread and butter.

> Since 8i Oracle has also supported a more advanced version
> where you can open
> the standby database in read-only mode.

This mode requires more thought, but is certainly possible, in time.

Best Regards

Simon Riggs