Re: Online checksums verification in the backend

From: Andres Freund <andres(at)anarazel(dot)de>
To: Julien Rouhaud <rjuju123(at)gmail(dot)com>
Cc: Michael Paquier <michael(at)paquier(dot)xyz>, Justin Pryzby <pryzby(at)telsasoft(dot)com>, Masahiko Sawada <masahiko(dot)sawada(at)2ndquadrant(dot)com>, Robert Haas <robertmhaas(at)gmail(dot)com>, PostgreSQL Hackers <pgsql-hackers(at)lists(dot)postgresql(dot)org>, Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)com>
Subject: Re: Online checksums verification in the backend
Date: 2020-10-30 05:08:52
Message-ID: 20201030050852.5eenoh3sk2uxnv53@alap3.anarazel.de
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On 2020-10-30 11:58:13 +0800, Julien Rouhaud wrote:
> So I'm assuming that the previous optimization to avoid almost every
> time doing an IO while holding a buffer mapping lock isn't an option?
> In that case, I don't see any other option than reverting the patch
> and discussing a new approach.

I think its pretty much *never* OK to do IO while holding a buffer
mapping lock. You're locking a significant fraction of shared buffers
over IO. That's just not OK. Don't think there's any place doing so
currently either.

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