Re: [Patch] Make pg_checksums skip foreign tablespace directories

Am Dienstag, den 18.02.2020, 15:15 +0900 schrieb Michael Paquier:
> Fair point.  Now, while the proposed patch is right to use
> TABLESPACE_VERSION_DIRECTORY, shouldn't we use strncmp based on the
> length of TABLESPACE_VERSION_DIRECTORY instead of de->d_name?  It
> seems also to me that the code as proposed is rather fragile, and
> that
> we had better be sure that the check only happens when we are
> scanning
> entries within pg_tblspc.
> 

Yes, after thinking and playing around with it a little i share your
position. You can still easily cause pg_checksums to error out by just
having arbitrary files around in the reference tablespace locations.
Though i don't think this is something of a big issue, it looks strange
and misleading if pg_checksums just complains about files not belonging
to the scanned PostgreSQL data directory (even we explicitly note in
the docs that even tablespace locations are somehow taboo for DBAs to
put other files and/or directories in there).

So i propose a different approach like the attached patch tries to
implement: instead of just blindly iterating over directory contents
and filter them out, reference the tablespace location and
TABLESPACE_VERSION_DIRECTORY directly. This is done by a new function
scan_tablespaces() which is specialized in just follow the
symlinks/junctions in pg_tblspc and call scan_directory() with just
what it has found there. It will also honour directories, just in case
an experienced DBA has copied over the tablespace into pg_tblspc
directly.

> The issue with pg_internal.init.XX is quite different, so I think
> that
> it would be better to commit that separately first.

Agreed.

Thanks,
	Bernd