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From: Tom Lane <[email protected]>
To: [email protected]
Cc: alex work <[email protected]>
Cc: Robert Haas <[email protected]>
Subject: Re: Slow GRANT ROLE on PostgreSQL 16 with thousands of ROLEs
Date: Thu, 21 Mar 2024 16:31:45 -0400
Message-ID: <[email protected]> (raw)
In-Reply-To: <[email protected]>
References: <CAGvXd3OSMbJQwOSc-Tq-Ro1CAz=vggErdSG7pv2s6vmmTOLJSg@mail.gmail.com>
	<[email protected]>
	<[email protected]>

I wrote:
> ... I still see the problematic GRANT taking ~250ms, compared
> to 5ms in v15.  roles_is_member_of is clearly on the hook for that.

Ah: looks like that is mainly the fault of the list_append_unique_oid
calls in roles_is_member_of.  That's also an O(N^2) cost of course,
though with a much smaller constant factor.

I don't think we have any really cheap way to de-duplicate the role
OIDs, especially seeing that it has to be done on-the-fly within the
collection loop, and the order of roles_list is at least potentially
interesting.  Not sure how to make further progress without a lot of
work.

			regards, tom lane

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