Horton

Re: API stability [was: pgsql: Fix possible recovery trouble if TRUNCATE overlaps a checkpoint.]

Markus Wanner <markus.wanner@enterprisedb.com>

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From: Markus Wanner <markus.wanner@enterprisedb.com>
To: Robert Haas <robertmhaas@gmail.com>
Cc: Michael Paquier <michael@paquier.xyz>, Tom Lane <tgl@sss.pgh.pa.us>, "pgsql-hackers@postgresql.org" <pgsql-hackers@postgresql.org>, Kyotaro Horiguchi <horikyota.ntt@gmail.com>
Date: 2022-04-11T19:45:59Z
Lists: pgsql-hackers 
On Mon, 2022-04-11 at 15:21 -0400, Robert Haas wrote:
> ... before v13, the commit in question actually
> changed the size of PGXACT, which is really quite bad -- it needs to
> be 12 bytes for performance reasons. And there's no spare bytes
> available, so I think we should follow one of the suggestions that he
> had over in that email thread, and put delayChkptEnd in PGPROC even
> though delayChkpt is in PGXACT.

This makes sense to me.  Kudos to Kyotaro for considering this.

At first read, this sounded like a trade-off between compatibility and
performance for PG 12 and older.  But I realize leaving delayChkpt in
PGXACT and adding just delayChkptEnd to PGPROC is compatible and leaves
PGXACT at a size of 12 bytes.  So this sounds like a good approach to
me.

Best Regards

Markus

Commits

  1. Rethink the delay-checkpoint-end mechanism in the back-branches.

  2. Rename delayChkpt to delayChkptFlags.

  3. Fix possible recovery trouble if TRUNCATE overlaps a checkpoint.