Re: Streaming replication and pg_xlogfile_name()

On Thu, 2010-02-25 at 12:02 +0900, Fujii Masao wrote:
> On Wed, Feb 24, 2010 at 7:56 AM, Simon Riggs <simon@2ndquadrant.com> wrote:
> > On Thu, 2010-01-28 at 10:28 +0200, Heikki Linnakangas wrote:
> >> Fujii Masao wrote:
> >> > In relation to the functions added recently, I found an annoying problem;
> >> > pg_xlogfile_name(pg_last_xlog_receive/replay_location()) might report the
> >> > wrong name because pg_xlogfile_name() always uses the current timeline,
> >> > and a backend doesn't know the actual timeline related to the location
> >> > which pg_last_xlog_receive/replay_location() reports. Even if a backend
> >> > knows that, pg_xlogfile_name() would be unable to determine which timeline
> >> > should be used.
> >>
> >> Hmm, I'm not sure what the use case for this is
> >
> > Agreed. What is the use case for this?
> 
> Since the current behavior would annoy many users (e.g., [*1]),
> I proposed to change it.
> 
> [*1]
> http://archives.postgresql.org/pgsql-hackers/2010-02/msg02014.php

OK, go for it.

If we expose the timeline as part of an "xlog location", then we should
do that everywhere as a change for 9.0. Clearly, "xlog location" has no
meaning without the timeline anyway, so this seems like a necessary
change not just a quick fix. It breaks compatibility, but since we're
changing replication in 9.0 that shouldn't be a problem.

-- Simon Riggs           www.2ndQuadrant.com