Message-ID: <bfca1010-e5f1-4e36-a461-61b6aad60c47@vondra.me>
Date: Mon, 3 Mar 2025 21:31:42 +0100
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Subject: Re: scalability bottlenecks with (many) partitions (and more)
To: Andres Freund <andres@anarazel.de>
Cc: Jakub Wartak <jakub.wartak@enterprisedb.com>,
 Robert Haas <robertmhaas@gmail.com>,
 PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
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From: Tomas Vondra <tomas@vondra.me>
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On 3/3/25 19:10, Andres Freund wrote:
> Hi,
> 
> On 2024-09-21 20:33:49 +0200, Tomas Vondra wrote:
>> I've finally pushed this, after many rounds of careful testing to ensure
>> no regressions, and polishing.
> 
> One minor nit: I don't like that FP_LOCK_SLOTS_PER_BACKEND is now non-constant
> while looking like a constant:
> 
> #define		FP_LOCK_SLOTS_PER_BACKEND	(FP_LOCK_SLOTS_PER_GROUP * FastPathLockGroupsPerBackend)
> 
> I don't think it's a good idea to have non-function-like #defines that
> reference variables that can change from run to run.
> 

Fair point, although it can't change "run to run" - not without a
restart. It's not a proper constant, of course, but it seemed close
enough. Yes, it might confuse people into thinking it's a constant, or
is there some additional impact?

The one fix I can think of is making it look more like a function,
possibly just like this:

#define	FastPathLockSlotsPerBackend() \
  (FP_LOCK_SLOTS_PER_GROUP * FastPathLockGroupsPerBackend)

Or do you have another suggestion?


regards

-- 
Tomas Vondra