Re: pg_upgrade resets timeline to 1

On Thu, May 28, 2015 at 10:13:14AM +0200, Christoph Berg wrote:
> Re: Bruce Momjian 2015-05-28 <20150527221607.GA7964@momjian.us>
> > Well, if you used pg_dump/pg_restore, you would have had even larger
> > problems as the file names would have matched.
> 
> True, but even here it's possible that files get overwritten. If you
> had a server running on TL 1 for files 0001001..00010020, and then did
> a PITR at location 10, you'll have a server writing to 00020010.
> If you pg_upgrade that, it will keep its WAL position, but start at 1
> again, overwriting files 00010011 and following.
> 
> > > > We could have pg_upgrade increment the timeline and allow for missing
> > > > history files, but that doesn't fix problems with non-pg_upgrade
> > > > upgrades, which also should never be sharing WAL files from previous
> > > > major versions.
> > > 
> > > pg_upgrade-style upgrades have a chance to know which timeline to use.
> > > That other methods have less knowledge about the "old" system
> > > shouldn't mean that pg_upgrade shouldn't care.
> > 
> > That is an open question, whether pg_upgrade should try to avoid this,
> > even if other methods do not, or should we better document not to do
> > this.
> 
> Actually, if initdb could be told to start at an arbitrary timeline,
> it would be trivial to avoid the problem with pg_dump upgrades as
> well.

Yes, that would make sense.  Perhaps we should revisit this for 9.6.

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