| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | pgsql-hackers(at)lists(dot)postgresql(dot)org |
| Cc: | alex work <alexwork033(at)gmail(dot)com>, Robert Haas <robertmhaas(at)gmail(dot)com> |
| Subject: | Re: Slow GRANT ROLE on PostgreSQL 16 with thousands of ROLEs |
| Date: | 2024-03-21 20:31:45 |
| Message-ID: | 642442.1711053105@sss.pgh.pa.us |
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| Lists: | pgsql-general pgsql-hackers |
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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