From: Tom Lane <tgl@sss.pgh.pa.us>
To: Robert Haas <robertmhaas@gmail.com>
cc: Thomas Munro <thomas.munro@gmail.com>,
        Peter Eisentraut <peter@eisentraut.org>,
        Larry Rosenman <ler@lerctr.org>,
        Pgsql hackers <pgsql-hackers@lists.postgresql.org>
Subject: Re: Fwd: Re: A new look at old NFS readdir() problems?
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Comments: In-reply-to Robert Haas <robertmhaas@gmail.com>
	message dated "Mon, 06 Jan 2025 09:20:18 -0500"
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Date: Mon, 06 Jan 2025 09:49:22 -0500
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Robert Haas <robertmhaas@gmail.com> writes:
> Yeah, that seems like very strong evidence against FreeBSD, but I
> think Thomas Munro's point about CIFS is worth considering. That is
> rather widely used, and if the same workarounds would help both that
> and FreeBSD's NFS, we might want to adopt it even if it's not a
> complete fix.

TBH, I am happy that PG is now failing in a fairly visible way on
filesystems that are broken in this fashion.  I think that is better
than silent data corruption in obscure circumstances, which is where
we were before and would be again if we band-aid rmtree() and do
nothing else.  Nor do I think it's worth the effort to try to become
fully bulletproof on the point.

I think we should document that CIFS is unsupported.  The docs
could say something like:

	Storing databases on filesystems with unreliable readdir() is
	not supported and can lead to data corruption.  If you observe
	warnings like "directory is not empty" when trying to drop a
	database, that is strong evidence that the filesystem has
	unreliable readdir().  Filesystems known to have this problem
	include NFS on FreeBSD and CIFS on all platforms.

We could s/FreeBSD/older FreeBSD/ if something comes of Thomas'
efforts to fix that situation.

			regards, tom lane