From: Tom Lane <tgl@sss.pgh.pa.us>
To: Nathan Bossart <nathandbossart@gmail.com>
cc: pgsql-hackers@lists.postgresql.org, alex work <alexwork033@gmail.com>,
        Robert Haas <robertmhaas@gmail.com>
Subject: Re: Slow GRANT ROLE on PostgreSQL 16 with thousands of ROLEs
In-reply-to: <20240325144743.GA2618709@nathanxps13>
References: <20240322005139.GA2060816@nathanxps13> <806361.1711069194@sss.pgh.pa.us> <20240322144739.GA2321246@nathanxps13> <20240322145532.GA2346110@nathanxps13> <907785.1711121266@sss.pgh.pa.us> <20240322163952.GA2347986@nathanxps13> <939945.1711126395@sss.pgh.pa.us> <20240322165448.GA2350322@nathanxps13> <20240322193506.GA2352051@nathanxps13> <1084642.1711140109@sss.pgh.pa.us> <20240325144743.GA2618709@nathanxps13>
Comments: In-reply-to Nathan Bossart <nathandbossart@gmail.com>
	message dated "Mon, 25 Mar 2024 09:47:43 -0500"
MIME-Version: 1.0
Content-Type: text/plain; charset="us-ascii"
Content-ID: <2490241.1711379319.1@sss.pgh.pa.us>
Date: Mon, 25 Mar 2024 11:08:39 -0400
Message-ID: <2490242.1711379319@sss.pgh.pa.us>
Archived-At: <https://www.postgresql.org/message-id/2490242.1711379319%40sss.pgh.pa.us>
Precedence: bulk

Nathan Bossart <nathandbossart@gmail.com> writes:
> Are there any changes you'd like to see for the Bloom patch [0]?  I'd like
> to see about getting that committed for v17.  One thing that crossed my
> mind is creating a combined list/filter that transparently created a filter
> when necessary (for reuse elsewhere), but I'm not sure that's v17 material.

Yeah, that thought occurred to me too, but I think we ought to have a
few more use-cases in view before trying to write an API.

As for the patch, I agree it could go into v17, but I think there is
still a little bit of work to do:

* The magic constants (crossover list length and bloom filter size)
need some testing to see if there are better values.  They should
probably be made into named #defines, too.  I suspect, with little
proof, that the bloom filter size isn't particularly critical --- but
I know we pulled the crossover of 1000 out of thin air, and I have
no certainty that it's even within an order of magnitude of being a
good choice.

* Code needs more than zero comments.

* Is it worth trying to make a subroutine, or at least a macro,
so as not to have 2 copies of the code?

			regards, tom lane