Horton

Re: avoid multiple hard links to same WAL file after a crash

Nathan Bossart <nathandbossart@gmail.com>

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From: Nathan Bossart <nathandbossart@gmail.com>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Robert Haas <robertmhaas@gmail.com>, Kyotaro Horiguchi <horikyota.ntt@gmail.com>, "pgsql-hackers@postgresql.org" <pgsql-hackers@postgresql.org>
Date: 2022-04-11T16:52:57Z
Lists: pgsql-hackers 
On Mon, Apr 11, 2022 at 12:28:47PM -0400, Tom Lane wrote:
> Robert Haas <robertmhaas@gmail.com> writes:
>> On Mon, Apr 11, 2022 at 5:12 AM Kyotaro Horiguchi
>> <horikyota.ntt@gmail.com> wrote:
>>> If this diagnosis is correct, the comment is proved to be paranoid.
> 
>> It's sometimes difficult to understand what problems really old code
>> comments are worrying about. For example, could they have been
>> worrying about bugs in the code? Could they have been worrying about
>> manual interference with the pg_wal directory? It's hard to know.
> 
> "git blame" can be helpful here, if you trace back to when the comment
> was written and then try to find the associated mailing-list discussion.
> (That leap can be difficult for commits pre-dating our current
> convention of including links in the commit message, but it's usually
> not *that* hard to locate contemporaneous discussion.)

I traced this back a while ago.  I believe the link() was first added in
November 2000 as part of f0e37a8.  This even predates WAL recycling, which
was added in July 2001 as part of 7d4d5c0.

-- 
Nathan Bossart
Amazon Web Services: https://aws.amazon.com

Commits

  1. Test restartpoints in archive recovery.

  2. Reset InstallXLogFileSegmentActive after walreceiver self-initiated exit.

  3. Skip WAL recycling and preallocation during archive recovery.

  4. Don't ERROR on PreallocXlogFiles() race condition.

  5. Revert "Add HINT for restartpoint race with KeepFileRestoredFromArchive()."

  6. Remove XLogFileInit() ability to unlink a pre-existing file.

  7. In XLogFileInit(), fix *use_existent postcondition to suit callers.

  8. Remove XLogFileInit() ability to skip ControlFileLock.

  9. Replace durable_rename_excl() by durable_rename(), take two

  10. Add HINT for restartpoint race with KeepFileRestoredFromArchive().

  11. Remove durable_rename_excl()

  12. Replace existing durable_rename_excl() calls with durable_rename()