Re: wrong fds used for refilenodes after pg_upgrade relfilenode changes Reply-To:

From: Justin Pryzby <pryzby(at)telsasoft(dot)com>
To: Andres Freund <andres(at)anarazel(dot)de>
Cc: pgsql-hackers(at)postgresql(dot)org, Robert Haas <robertmhaas(at)gmail(dot)com>, Thomas Munro <thomas(dot)munro(at)gmail(dot)com>
Subject: Re: wrong fds used for refilenodes after pg_upgrade relfilenode changes Reply-To:
Date: 2022-02-09 22:42:30
Message-ID: 20220209224230.GS31460@telsasoft.com
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On Wed, Feb 09, 2022 at 02:00:04PM -0800, Andres Freund wrote:
> On linux we can do so by a) checking if readlink(/proc/self/fd/$fd) points to
> a filename ending in " (deleted)", b) doing fstat(fd) and checking if st_nlink
> == 0.

You could also stat() the file in proc/self/fd/N and compare st_ino. It
"looks" like a symlink (in which case that wouldn't work) but it's actually a
Very Special File. You can even recover deleted, still-opened files that way..

PS. I didn't know pg_upgrade knew about Reply-To ;)

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