Horton

Re: standby recovery fails (tablespace related) (tentative patch and discussion)

Robert Haas <robertmhaas@gmail.com>

View thread View on postgr.es
From: Robert Haas <robertmhaas@gmail.com>
To: Alvaro Herrera <alvherre@alvh.no-ip.org>
Cc: Kyotaro Horiguchi <horikyota.ntt@gmail.com>, Michael Paquier <michael@paquier.xyz>, Julien Rouhaud <rjuju123@gmail.com>, "pgsql-hackers@postgresql.org" <pgsql-hackers@postgresql.org>
Date: 2022-03-28T16:17:50Z
Lists: pgsql-hackers 
On Mon, Mar 21, 2022 at 3:02 PM Alvaro Herrera <alvherre@alvh.no-ip.org> wrote:
> > 2. Why not instead change the code so that the operation can succeed,
> > by creating the prerequisite parent directories? Do we not have enough
> > information for that? I'm not saying that we definitely should do it
> > that way rather than this way, but I think we do take that approach in
> > some cases.
>
> It seems we can choose freely between these two implementations -- I
> mean I don't see any upsides or downsides to either one.

What got committed here feels inconsistent to me. Suppose we have a
checkpoint, and then a series of operations that touch a tablespace,
and then a drop database and drop tablespace. If the first operation
happens to be CREATE DATABASE, then this patch is going to fix it by
skipping the operation. However, if the first operation happens to be
almost anything else, the way it's going to reference the dropped
tablespace is via a block reference in a WAL record of a wide variety
of types. That's going to result in a call to
XLogReadBufferForRedoExtended() which will call
XLogReadBufferExtended() which will do smgrcreate(smgr, forknum, true)
which will in turn call TablespaceCreateDbspace() to fill in all the
missing directories.

I don't think that's very good. It would be reasonable to decide that
we're never going to create the missing directories and instead just
remember that they were not found so we can do a cross check. It's
also reasonable to just create the directories on the fly. But doing a
mix of those systems doesn't really seem like the right idea -
particularly because it means that the cross-check system is probably
not very effective at finding actual problems in the code.

Am I missing something here?

-- 
Robert Haas
EDB: http://www.enterprisedb.com

Commits

  1. Improve recently-added test reliability

  2. Fix new recovery test for log_error_verbosity=verbose case

  3. Fix test instability

  4. Fix replay of create database records on standby

  5. Allow "in place" tablespaces.

  6. Fix get_dirent_type() for Windows junction points.

  7. Revert "Fix replay of create database records on standby"

  8. Add end-to-end testing of pg_basebackup's tar-format output.

  9. Make DROP DATABASE command generate less WAL records.

  10. Consolidate methods for translating a Perl path to a Windows path.