Re: [HACKERS] WIP: long transactions on hot standby feedback replica / proof of concept

From: Robert Haas <robertmhaas(at)gmail(dot)com>
To: Alexander Korotkov <a(dot)korotkov(at)postgrespro(dot)ru>
Cc: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Andres Freund <andres(at)anarazel(dot)de>, Sawada Masahiko <sawada(dot)mshk(at)gmail(dot)com>, Ivan Kartyshov <i(dot)kartyshov(at)postgrespro(dot)ru>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: [HACKERS] WIP: long transactions on hot standby feedback replica / proof of concept
Date: 2018-09-02 20:46:49
Message-ID: CA+TgmobmA9VJOKQO1UuKurX7TPjVxFkYNAZPd8F2OOQ1kZS30A@mail.gmail.com
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On Mon, Aug 27, 2018 at 11:38 AM, Alexander Korotkov
<a(dot)korotkov(at)postgrespro(dot)ru> wrote:
> The aspect I'm more concerned here about is whether we miss ability
> for detecting some of IO errors, if we don't distinguish new pages
> from pages whose tuples were removed by vacuum.

My main concern is correctness. If we ever have valid-looking buffers
in shared_buffers after the corresponding data has been truncated away
on disk, we've got to make sure that nobody ever confuses one of them
with an actually-valid buffer. Reading over your algorithm, I can't
convince myself that you have that case nailed down tightly enough.

--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company

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