Re: Slow GRANT ROLE on PostgreSQL 16 with thousands of ROLEs

Nathan Bossart <nathandbossart(at)gmail(dot)com> writes:
> On Tue, Mar 26, 2024 at 02:16:03PM -0400, Tom Lane wrote:
>> ... I'm not sold on your "ROLES_LIST_BLOOM_THRESHOLD * 10"
>> value. Maybe it doesn't matter though.

> Yeah, I wasn't sure how much to worry about this. I figured that we might
> as well set it to a reasonable estimate based on the description of the
> parameter. This description claims that the filter should work well if
> this is off by a factor of 5 or more, and 50x the threshold sounded like it
> ought to be good enough for anyone, so that's how I landed on 10x. But as
> you point out, this value will be disregarded altogether, and it will
> continue to be ignored unless the filter implementation changes, which
> seems unlikely. If you have a different value in mind that you would
> rather use, I'm fine with changing it.

No, I have no better idea. As you say, we should try to provide some
semi-reasonable number in case bloom_create ever starts paying
attention, and this one seems fine.

>> I do not like, even a little bit, your use of a static variable to
>> hold the bloom filter pointer.

> Ah, yes, that's no good. I fixed this in the new version.

My one remaining suggestion is that this comment isn't very precise
about what's happening:

* If there is a previously-created Bloom filter, use it to determine
* whether the role is missing from the list. Otherwise, do an ordinary
* linear search through the existing role list.

Maybe more like

* If there is a previously-created Bloom filter, use it to try to
* determine whether the role is missing from the list. If it
* says yes, that's a hard fact and we can go ahead and add the
* role. If it says no, that's only probabilistic and we'd better
* search the list. Without a filter, we must always do an ordinary
* linear search through the existing list.

LGTM other than that nit.

regards, tom lane