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: Robert Haas <robertmhaas@gmail.com>
Cc: Thomas Munro <thomas.munro@gmail.com>, Andres Freund <andres@anarazel.de>, Peter Geoghegan <pg@bowt.ie>, "pgsql-hackers@postgresql.org" <pgsql-hackers@postgresql.org>, Kevin Grittner <kgrittn@gmail.com>
Date: 2021-06-15T19:49:03Z
Lists: pgsql-hackers
Robert Haas <robertmhaas@gmail.com> writes:
> My general point here is that I would like to know whether we have a
> finite number of reasonably localized bugs or a three-ring disaster
> that is unrecoverable no matter what we do. Andres seems to think it
> is the latter, and I *think* Peter Geoghegan agrees, but I think that
> the point might be worth a little more discussion.

TBH, I am not clear on that either.

> I'm unclear whether
> Tom's dislike for the feature represents hostility to the concept -
> with which I would have to disagree - or a judgement on the quality of
> the implementation - which might be justified.

I think it's a klugy, unprincipled solution to a valid real-world
problem.  I suspect the implementation issues are not unrelated to
the kluginess of the concept.  Thus, I would really like to see us
throw this away and find something better.  I admit I have nothing
to offer about what a better solution to the problem would look like.
But I would really like it to not involve random-seeming query failures.

			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.