Date: Wed, 19 Sep 2018 11:53:02 +0900
From: Michael Paquier <michael@paquier.xyz>
To: Adrien NAYRAT <adrien.nayrat@anayrat.info>
Cc: pgsql-docs@lists.postgresql.org
Subject: Re: Mention FK creation take ShareRowExclusiveLock on referenced
 table
Message-ID: <20180919025302.GF1650@paquier.xyz>
References: <c4e8af11-1dfc-766a-c953-76979b9fcdaa@anayrat.info>
MIME-Version: 1.0
Content-Type: multipart/signed; micalg=pgp-sha512;
	protocol="application/pgp-signature"; boundary="t4apE7yKrX2dGgJC"
Content-Disposition: inline
In-Reply-To: <c4e8af11-1dfc-766a-c953-76979b9fcdaa@anayrat.info>
Precedence: bulk


--t4apE7yKrX2dGgJC
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
Content-Transfer-Encoding: quoted-printable

On Tue, Sep 18, 2018 at 12:32:54PM +0200, Adrien NAYRAT wrote:
> A few days ago I was surprised a CREATE TABLE containing FK constraint was
> stuck due to an automatic vacuum freeze (which took ShareUpdateExclusiveL=
ock
> if I remember) on referenced table.

Right.  See the top of vacuum_rel() where lmode is set.

> After digging into the code I found theses lines in tablecmds.c :
>=20
> /*
>  * Grab ShareRowExclusiveLock on the pk table, so that someone doesn't
>  * delete rows out from under us.
>  */
>=20
> Maybe it should be documented in theses pages?
>=20
> https://www.postgresql.org/docs/current/static/sql-createtable.html
> https://www.postgresql.org/docs/current/static/sql-altertable.html
>=20
> If you agree I can send a patch.

That looks like a good idea.  Are you thinking about adding a comment
about that in "ADD table_constraint" for the ALTER TABLE page, and in
"FOREIGN KEY" for the CREATE TABLE page?
--
Michael

--t4apE7yKrX2dGgJC
Content-Type: application/pgp-signature; name="signature.asc"

-----BEGIN PGP SIGNATURE-----
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=rnLK
-----END PGP SIGNATURE-----

--t4apE7yKrX2dGgJC--