Re: pg_rewind vs superuser

On Fri, Apr 05, 2019 at 09:41:58AM +0200, Michael Banck wrote:
> Is there a good reason why Postgres doesn't just issue a CHECKPOINT
> after promote itself? After all, this seems to be about making the
> control file having the proper content, which sounds like a good thing
> to have in general.

The startup process requests a checkpoint since 9.3, and before that
it was doing the checkpoint by itself (grep for fast_promoted and
RequestCheckpoint() around line 7579 in xlog.c). This allows the
recovery to finish much faster.

> Could this be a problem for anything else besides pg_rewind?

Not that I know of, at least not in the tree.

> This looks like a needless footgun waiting to happen, and just
> documenting it in pg_rewind's notes section looks a bit too hidden to me
> (but is certainly an improvement).

We had a couple of reports on the matter over the past years. Perhaps
we could use a big fat warning but that feels a bit overdoing it.
--
Michael