Message-ID: <56d92102952fff2283f05b8d7712e34bad4647e4.camel@cybertec.at>
Subject: Re: Transaction wraparound and read committed isolation level
From: Laurenz Albe <laurenz.albe@cybertec.at>
To: h@husseinnasser.com, pgsql-docs@lists.postgresql.org
Date: Tue, 21 Feb 2023 10:51:42 +0100
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On Sun, 2023-02-19 at 03:10 +0000, PG Doc comments form wrote:
> The following documentation comment has been logged on the website:
>=20
> Page: https://www.postgresql.org/docs/15/routine-vacuuming.html
> Description:
>=20
> hey guys
>=20
> thanks for the work you do we really appreciate it.=20
>=20
> In the transaction wraparound section this statement is misleading and go=
t
> me really confused.=20
>=20
> =E2=80=9Ca row version with an insertion XID greater than the current tra=
nsaction's
> XID is =E2=80=9Cin the future=E2=80=9D and should not be visible to the c=
urrent
> transaction=E2=80=9C
>=20
> If the current transaction isolation level is read committed it absolutel=
y
> can see rows committed by future transactions with higher XIDs.

You are right, in combination with PlanQualEval you can.

> Would be cool to add a note.=20
>=20
> this also bear the question that the wraparound isn=E2=80=99t really a pr=
oblem with
> default isolation level but more for higher levels such as repeatable rea=
d
> and such.=20
>=20
> please correct me if my understanding is incorrect.

Wraparound can be a problem on all isolation levels.  It has to do with
transaction IDs and visibility.

Yours,
Laurenz Albe