Re: Mention FK creation take ShareRowExclusiveLock on referenced table

On 9/19/18 4:53 AM, Michael Paquier wrote:
> 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?

Yes, here is the patch

Thanks

--
Adrien