Allow wal_keep_segments to keep all segments

Bruce Momjian wrote:
> Robert Haas wrote:
> > On Sat, May 8, 2010 at 10:40 PM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
> > > Bruce Momjian <bruce@momjian.us> writes:
> > >> Uh, did we decide that 'wal_keep_segments' was the best name for this
> > >> GUC setting? ?I know we shipped beta1 using that name.
> > >
> > > I thought min_wal_segments was a reasonable proposal, but it wasn't
> > > clear if there was consensus or not.
> > 
> > I think most people thought it was another reasonable choice, but I
> > think the consensus position is probably something like "it's about
> > the same" rather than "it's definitely better".  We had one or two
> > people with stronger opinions than that on either side, I believe.
> 
> Agreed the current name seems OK.  However, was there agreement that
> wal_keep_segments = -1 should keep all WAL segements?  I can see that as
> useful for cases where you are doing a dump to be transfered to the
> slave, and not using archive_command.  This avoids the need for the "set
> a huge value" solution.

The attached patch allows wal_keep_segments = -1 to keep all segements; 
this is particularly useful for taking a base backup, where you need all
the WAL files during startup of the standby.  I have documented this
usage in the patch as well.

I am thinking of applying this after 9.0 beta2 if there is no objection.

-- 
  Bruce Momjian  <bruce@momjian.us>        http://momjian.us
  EnterpriseDB                             http://enterprisedb.com

  + None of us is going to be here forever. +