On Thu, Mar 21, 2024 at 04:31:45PM -0400, Tom Lane wrote: > 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.
Assuming these are larger lists, this might benefit from optimizations involving SIMD intrinsics. I looked into that a while ago [0], but the effort was abandoned because we didn't have any concrete use-cases at the time. (I'm looking into some additional optimizations in a separate thread [1] that would likely apply here, too.) [0] https://postgr.es/m/20230308002502.GA3378449%40nathanxps13 [1] https://postgr.es/m/20240321183823.GA1800896%40nathanxps13 -- Nathan Bossart Amazon Web Services: https://aws.amazon.com
