Horton

Re: Race between KeepFileRestoredFromArchive() and restartpoint

Kyotaro Horiguchi <horikyota.ntt@gmail.com>

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From: Kyotaro Horiguchi <horikyota.ntt@gmail.com>
To: noah@leadboat.com
Cc: don@seiler.us, david@pgmasters.net, pgsql-hackers@postgresql.org
Date: 2022-08-03T08:15:17Z
Lists: pgsql-hackers 
At Wed, 3 Aug 2022 00:28:47 -0700, Noah Misch <noah@leadboat.com> wrote in 
> On Wed, Aug 03, 2022 at 11:24:17AM +0900, Kyotaro Horiguchi wrote:
> > At Tue, 2 Aug 2022 16:03:42 -0500, Don Seiler <don@seiler.us> wrote in 
> > > could not link file “pg_wal/xlogtemp.18799" to
> > > > “pg_wal/000000010000D45300000010”: File exists
> 
> > Hmm.  It seems like a race condition betwen StartupXLOG() and
> > RemoveXlogFIle(). We need wider extent of ContolFileLock. Concretely
> > taking ControlFileLock before deciding the target xlog file name in
> > RemoveXlogFile() seems to prevent this happening. (If this is correct
> > this is a live issue on the master branch.)
> 
> RemoveXlogFile() calls InstallXLogFileSegment() with find_free=true.  The
> intent of find_free=true is to make it okay to pass a target xlog file that
> ceases to be a good target.  (InstallXLogFileSegment() searches for a good
> target while holding ControlFileLock.)  Can you say more about how that proved
> to be insufficient?

Ug.. No. I can't. I was confused by something. Sorry.

PreallocXlogFiles() and checkpointer are mutually excluded by the same
lock, too.

regards.

-- 
Kyotaro Horiguchi
NTT Open Source Software Center

Commits

  1. Skip WAL recycling and preallocation during archive recovery.

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

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

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

  5. Remove XLogFileInit() ability to skip ControlFileLock.

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

  7. Complete TODO item: