Re: PITR promote bug: Checkpointer writes to older timeline

At Thu, 4 Mar 2021 11:18:42 +0900, Michael Paquier <michael@paquier.xyz> wrote in 
> On Thu, Mar 04, 2021 at 10:28:31AM +0900, Kyotaro Horiguchi wrote:
> > read_local_xlog_page() works as a part of logical decoding and has
> > responsibility to update ThisTimeLineID properly.  As the comment in
> > the function, it is the proper place to update ThisTimeLineID since we
> > miss a timeline change if we check it earlier and the function uses
> > the value just after. So we cannot change that behavior of the
> > function.  That is, neither of them doesn't seem to be the right fix.
> > 
> > The confusion here is that there's two ThisTimeLineID's here. The
> > previous TLI for read and the next TLI to write.  Most part of the
> > function is needed to read a 2pc recrod so the ways we can take here
> > is:
> > 
> > 1. Somehow tell the function not to update ThisTimeLineID in specific
> >   cases. This can be done by xlogreader private data but this doesn't
> >   seem reasonable.
> > 
> > 2. Restore ThisTimeLineID after calling XLogReadRecord() in the
> >   *caller* side.  This is what came up to me first but I don't like
> >   this, too, but I don't find better fix.  way.
> 
> I have not looked in details at the solutions proposed here, but could
> it be possible to have a TAP test at least please?  Seeing the script
> from the top of the thread, it should not be difficult to do so.  I
> would put that in a file different than 009_twophase.pl, within
> src/test/recovery/.

Year, agreed. It is needed as the final patch. That situation is
easily caused. I'm not sure how to detect the corruption yet, though.
I'll consider that.

regards.

-- 
Kyotaro Horiguchi
NTT Open Source Software Center