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From: Tom Lane <tgl@sss.pgh.pa.us>
To: Michael Paquier <michael@paquier.xyz>
cc: pgsql-hackers@lists.postgresql.org
Subject: Re: Relations being opened without any lock whatever
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 <20180930232919.GC2595@paquier.xyz>
Comments: In-reply-to Michael Paquier <michael@paquier.xyz>
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Michael Paquier <michael@paquier.xyz> writes:
> Okay, that's bad.  Wouldn't it be sufficient to use what the caller
> passes out as lockmode instead of enforcing AEL though?

No, because at the bottom of that function we're going to do a DROP
CONSTRAINT on the old FK constraint, and that needs AEL anyway.
If we tried to take a lesser lock first we'd just be creating a
lock-upgrade deadlock risk.

			regards, tom lane