Re: pg_rewind fails on Windows where tablespaces are used

On Wed, May 08, 2024 at 03:02:21PM +0700, Chris Travers wrote:
> Setup is PostgreSQL on Windows with a tablespace on a separate drive. When
> I go to run pg_rewind it consistently fails with the following error:

(Chris has poked me regarding this issue last week in Vancouver.)

> pg_rewind: servers diverged at WAL location 39B/7EC6F60 on timeline 2
> pg_rewind: rewinding from last common checkpoint at 39B/7E8E3F8 on timeline
> 2
> pg_rewind: error: file "pg_tblspc/34244696" is of different type in source
> and target
>
> The file is confirmed to be a JUNCTION to the correct location on both the
> source and target. So the error looks like a problem interacting with
> Windows and detecting JUNCTION types in this case.

I am not completely sure to follow here. Aren't you making use of an
in-place tablespace here? Could you provide more details about the
structure of the data folders, because these are on separate hosts,
right? When rewinding from a live server, readlink() returns an
absolute path for a junction point, meaning that the result would not
be influenced by bf227926d22b as we would always handle such an entry
with FILE_TYPE_SYMLINK. On Windows, the link creation would be
covered by pgsymlink(), which would create the link as a junction
point.

Note that I do not object to a backpatch of bf227926d22b, as I did not
do it for the sake of caution as in-place tablespaces are a developer
feature. If you use it for tests of your own on stable branches,
well, why not.

> I came across the following which looks like it would fix this problem but
> don't have a proper build environment. Please consider backporting the fix
> at least as far as Postgres 15 as this bug fix does apply to non-in-place
> tablespaces on Windows. The thread is
> https://postgrespro.com/list/thread-id/2657122

I'd suggest to use the postgresql.org reference. This refers to
commit bf227926d22b, for the following thread:
https://www.postgresql.org/message-id/2b79d2a8-b2d5-4bd7-a15b-31e485100980.xiyuan.zr@alibaba-inc.com

Thanks,
--
Michael