Re: snapshot too old issues, first around wraparound and then more.

Tom Lane <tgl@sss.pgh.pa.us>

From: Tom Lane <tgl@sss.pgh.pa.us>
To: Peter Geoghegan <pg@bowt.ie>
Cc: Robert Haas <robertmhaas@gmail.com>, Thomas Munro <thomas.munro@gmail.com>, Andres Freund <andres@anarazel.de>, "pgsql-hackers@postgresql.org" <pgsql-hackers@postgresql.org>, Kevin Grittner <kgrittn@gmail.com>
Date: 2021-06-15T18:01:40Z
Lists: pgsql-hackers
Peter Geoghegan <pg@bowt.ie> writes:
> On Tue, Jun 15, 2021 at 9:51 AM Tom Lane <tgl@sss.pgh.pa.us> wrote:
>> So, it's well over a year later, and so far as I can see exactly
>> nothing has been done about snapshot_too_old's problems.

> I propose that the revert question be explicitly timeboxed. If the
> issues haven't been fixed by some date, then "snapshot too old"
> automatically gets reverted without further discussion. This gives
> qualified hackers the opportunity to save the feature if they feel
> strongly about it, and are actually willing to take responsibility for
> its ongoing maintenance.

The goal I have in mind is for snapshot_too_old to be fixed or gone
in v15.  I don't feel a need to force the issue sooner than that, so
there's plenty of time for someone to step up, if anyone wishes to.

I imagine that we should just ignore the question of whether anything
can be done for it in the back branches.  Given the problems
identified upthread, fixing it in a non-back-patchable way would be
challenging enough.

			regards, tom lane



Commits

  1. Remove the "snapshot too old" feature.

  2. Improve timeout.c's handling of repeated timeout set/cancel.

  3. Fix two bugs in MaintainOldSnapshotTimeMapping.