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

I wrote:
> It looks like part of the blame might be ascribable to catcache.c,
> as if you look at the problem microscopically you find that
> roles_is_member_of is causing catcache to make a ton of AUTHMEMMEMROLE
> catcache lists, and SearchSysCacheList is just iterating linearly
> through the cache's list-of-lists, so that search is where the O(N^2)
> time is actually getting taken.  Up to now that code has assumed that
> any one catcache would not have very many catcache lists.  Maybe it's
> time to make that smarter; but since we've gotten away with this
> implementation for decades, I can't help feeling that the real issue
> is with roles_is_member_of's usage pattern.

I wrote a quick finger exercise to make catcache.c use a hash table
instead of a single list for CatCLists, modeling it closely on the
existing hash logic for simple catcache entries.  This helps a good
deal, but I still see the problematic GRANT taking ~250ms, compared
to 5ms in v15.  roles_is_member_of is clearly on the hook for that.

			regards, tom lane