From: | Peter Geoghegan <pg(at)bowt(dot)ie> |
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To: | Andres Freund <andres(at)anarazel(dot)de> |
Cc: | Alvaro Herrera <alvherre(at)alvh(dot)no-ip(dot)org>, "Wood, Dan" <hexpert(at)amazon(dot)com>, pgsql-committers <pgsql-committers(at)postgresql(dot)org>, "Wong, Yi Wen" <yiwong(at)amazon(dot)com>, Michael Paquier <michael(dot)paquier(at)gmail(dot)com>, Robert Haas <robertmhaas(at)gmail(dot)com>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, PostgreSQL Hackers <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: [HACKERS] pgsql: Fix freezing of a dead HOT-updated tuple |
Date: | 2017-11-10 01:13:40 |
Message-ID: | CAH2-WzknEHKn8rEQ_tL0USywARTU-b3fAenVBPprZqGzp1Z+4g@mail.gmail.com |
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Lists: | pgsql-committers pgsql-hackers |
On Thu, Nov 9, 2017 at 4:53 PM, Andres Freund <andres(at)anarazel(dot)de> wrote:
> Primarily because it's not an anti-corruption tool. I'd be surprised if
> there weren't ways to corrupt the page using these corruptions that
> aren't detected by it.
It's very hard to assess the risk of missing something that's actually
detectable with total confidence, but I think that the check is actually
very thorough.
> But even if it were, I don't think there's
> enough information to do so in the general case. You very well can end
> up with pages where subsequent hot pruning has removed a good bit of the
> direct evidence of this bug.
Sure, but maybe those are cases that can't get any worse anyway. So the
question of avoiding making it worse doesn't arise.
> But I'm not really sure why the error detection capabilities of matter
> much for the principal point I raised, which is how much work we need to
> do to not further worsen the corruption.
You're right. Just trying to put the risk in context, and to understand the
extent of the concern that you have.
--
Peter Geoghegan
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