Re: Using pg_upgrade on log-shipping standby servers

On Tue, Jul 17, 2012 at 04:49:39PM -0700, Daniel Farina wrote:
> On Tue, Jul 17, 2012 at 11:55 AM, Jeff Davis <pgsql(at)j-davis(dot)com> wrote:
> > On Tue, 2012-07-17 at 01:02 -0700, Daniel Farina wrote:
> >> Could pg_upgrade emit WAL segment(s) to provide continuity of a
> >> timeline? So something like:
> >
> > By "segments" did you mean "records"?
>
> Yes. It would be nicer not to have to tie it to the WAL segment file size.
>
> >> * Take down the writable primary for pg_upgrade
> >> * Some WAL is emitted and possibly archived
> >> * The old version, when reaching the special pg_upgrade WAL, could
> >> exit or report its situation having paused replay (as clearly, it
> >> cannot proceed). Unsure.
> >
> > I don't really understand this step.
>
> "Some WAL is emitted and possibly archived" needs a subject in that fragment:
>
> "pg_upgrade somehow (directly, or indirectly) emits and/or archives
> WAL used to complete binary-upgrade". That means that it should
> appear in the WAL stream and be subject to archive_command, like any
> other WAL.
>
> The sticky part is what the standby should do when it encounters the
> special wal-upgrade records. It should probably pause replay to allow
> some other program to stop the old postgres version and start the new
> version with the same cluster.

WAL is not guaranteed to be the same between PG major versions, so doing
anything with WAL is pretty much a no-go.

--
Bruce Momjian <bruce(at)momjian(dot)us> http://momjian.us
EnterpriseDB http://enterprisedb.com

+ It's impossible for everything to be true. +