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From: Michael Paquier <[email protected]>
To: Adrien NAYRAT <[email protected]>
Cc: [email protected]
Subject: Re: Mention FK creation take ShareRowExclusiveLock on referenced table
Date: Wed, 19 Sep 2018 11:53:02 +0900
Message-ID: <[email protected]> (raw)
In-Reply-To: <[email protected]>
References: <[email protected]>

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 ShareUpdateExclusiveLock
> 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 :
> 
> /*
>  * Grab ShareRowExclusiveLock on the pk table, so that someone doesn't
>  * delete rows out from under us.
>  */
> 
> Maybe it should be documented in theses pages?
> 
> https://www.postgresql.org/docs/current/static/sql-createtable.html
> https://www.postgresql.org/docs/current/static/sql-altertable.html
> 
> 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


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