Message-ID: <96e63393bffdf23b4ea853a9ddebed1ed0acc670.camel@cybertec.at>
Subject: Re: What's the best practice to compare the transaction with the
 checkpoint?
From: Laurenz Albe <laurenz.albe@cybertec.at>
To: Jialun Zhang <reatank@gmail.com>, Tom Lane <tgl@sss.pgh.pa.us>
Cc: pgsql-novice@lists.postgresql.org
Date: Tue, 07 Jul 2020 11:41:46 +0200
In-Reply-To: 
 <CAMFL+JhXVq45tOgNgWvhXU5s0SGUEcM7Oajuy488fZ4vh8CCtw@mail.gmail.com>
References: 
	<CAMFL+Jg88HxVL75db9HY_QebL+iLGAH4p-0Drmii4z1m6QD7aw@mail.gmail.com>
	 <0bf46f63bd9f7e57a83710644a0ed4cf5f6c52f0.camel@cybertec.at>
	 <CAMFL+JjnQE8NWP1vMxfzJXFyjCP-9yvA6ku6FkJAjTpRkOoyTg@mail.gmail.com>
	 <0e86755d-57aa-9c31-31d2-f90b61456c96@verizon.net>
	 <CAMFL+JisTCugv5T8n=gQNFKcvWMMJwARz1sWwhv1nQ8=EKvQTQ@mail.gmail.com>
	 <1377221.1594050275@sss.pgh.pa.us>
	 <CAMFL+JiRTm9Ymz+rkEVL9TOZXrwx9LPecBZeFGKy-BKTQ3T34g@mail.gmail.com>
	 <1380011.1594053288@sss.pgh.pa.us>
	 <CAMFL+JhXVq45tOgNgWvhXU5s0SGUEcM7Oajuy488fZ4vh8CCtw@mail.gmail.com>
Content-Type: text/plain; charset="UTF-8"
User-Agent: Evolution 3.32.5 (3.32.5-1.fc30) 
MIME-Version: 1.0
Content-Transfer-Encoding: 7bit
Precedence: bulk

On Mon, 2020-07-06 at 17:50 -0400, Jialun Zhang wrote:
> > The replay of step 4 would need to perform something like "delete the file
> > for V if it exists, but don't complain if it does not", since we couldn't
> > be sure which state we'll find on-disk.
>
> What I am actually asking is that, is it possible that the replay depends
> on a deleted value, which has been physically removed by a VACUUM.
> Bear with my very basic knowledge in Postgres.

The WAL records that affect your out-of-line stored file would be written
by you, so you'd have to make sure that replaying such WAL records works
whether the file is present or not.

Yours,
Laurenz Albe
-- 
Cybertec | https://www.cybertec-postgresql.com