Re: [COMMITTERS] pgsql: Fix freezing of a dead HOT-updated tuple

From: Peter Geoghegan <pg(at)bowt(dot)ie>
To: "Wood, Dan" <hexpert(at)amazon(dot)com>
Cc: Michael Paquier <michael(dot)paquier(at)gmail(dot)com>, Alvaro Herrera <alvherre(at)2ndquadrant(dot)com>, PostgreSQL Hackers <pgsql-hackers(at)postgresql(dot)org>, "Wong, Yi Wen" <yiwong(at)amazon(dot)com>
Subject: Re: [COMMITTERS] pgsql: Fix freezing of a dead HOT-updated tuple
Date: 2017-10-04 01:19:56
Message-ID: CAH2-WzmtGabEF75yg2nW1HqNyx0Tmq2xrcG40hvJ7-OfPKnzQQ@mail.gmail.com
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On Tue, Oct 3, 2017 at 6:09 PM, Wood, Dan <hexpert(at)amazon(dot)com> wrote:
> I’ve just started looking at this again after a few weeks break.

> if (TransactionIdIsValid(priorXmax) &&
> !TransactionIdEquals(priorXmax, HeapTupleHeaderGetXmin(htup)))
> break;

> We need to understand why these TXID equal checks exist. Can we differentiate the cases they are protecting against with the two exceptions I’ve found?

I haven't read your remarks here in full, since I'm about to stop
working for the day, but I will point out that
src/backend/access/heap/README.HOT says a fair amount about this,
under "Abort Cases".

--
Peter Geoghegan

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