From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
---|---|
To: | Nathan Bossart <nathandbossart(at)gmail(dot)com> |
Cc: | pgsql-hackers(at)lists(dot)postgresql(dot)org, 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: | 2024-03-22 16:53:15 |
Message-ID: | 939945.1711126395@sss.pgh.pa.us |
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Nathan Bossart <nathandbossart(at)gmail(dot)com> writes:
> On Fri, Mar 22, 2024 at 11:27:46AM -0400, Tom Lane wrote:
>> * Do we want to risk back-patching any of this, to fix the performance
>> regression in v16? I think that the OP's situation is a pretty
>> narrow one, but maybe he's not the only person who managed to dodge
>> roles_is_member_of's performance issues in most other cases.
> I've heard complaints about performance with many roles before, so I
> certainly think this area is worth optimizing. As far as back-patching
> goes, my current feeling is that the hash table is probably pretty safe and
> provides the majority of the benefit, but anything fancier should probably
> be reserved for v17 or v18.
Yeah. Although both the catcache and list_append_unique_oid bits
are O(N^2), the catcache seems to have a much bigger constant
factor --- when I did a "perf" check on the unpatched code,
I saw catcache eating over 90% of the runtime and list_member_oid
about 2%. So let's fix that part in v16 and call it a day.
It should be safe to back-patch the catcache changes as long as
we put the new fields at the end of the struct and leave cc_lists
present but empty.
Would you like to review the catcache patch further, or do you
think it's good to go?
regards, tom lane
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