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@j-davis.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@momjian.us>        http://momjian.us
  EnterpriseDB                             http://enterprisedb.com

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