Message-ID: <0f708be9-c95b-421d-8ee4-a41455bfb64a@iki.fi>
Date: Sat, 4 Apr 2026 02:58:42 +0300
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Subject: Re: Shared hash table allocations
From: Heikki Linnakangas <hlinnaka@iki.fi>
To: Ashutosh Bapat <ashutosh.bapat.oss@gmail.com>
Cc: Tomas Vondra <tomas@vondra.me>,
 "pgsql-hackers@postgresql.org" <pgsql-hackers@postgresql.org>,
 Robert Haas <robertmhaas@gmail.com>, Rahila Syed <rahilasyed90@gmail.com>,
 Matthias van de Meent <boekewurm+postgres@gmail.com>
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On 03/04/2026 20:32, Heikki Linnakangas wrote:
> On 03/04/2026 16:03, Ashutosh Bapat wrote:
>> On Thu, Apr 2, 2026 at 10:15 PM Heikki Linnakangas <hlinnaka@iki.fi> 
>> wrote:
>>>> I think the release notes should "nudge" all the
>>>> users who use non-default max_locks_per_transaction to increase it if
>>>> they see "out of memory" errors. I don't think it should provide a
>>>> blanket advise to double their locks
>>>
>>> How about:
>>>
>>> "If you had previously set max_locks_per_transaction, you might need to
>>> set it to a higher value in v19 to avoid "out of shared memory" errors.
>>> If you are unsure what to set it to and don't mind the increased memory
>>> usage, you can double the value to ensure that you can acquire at least
>>> as many locks as before"
>>
>> The wiggle room is 100KB fixed + 10% of other two structures, so value
>> by which it should be increased is partly fixed and partly a multiple
>> of current value. "double the value" is simplest advice we can give.
>> +1.
> 
> Ok, committed these patches to remove the safety margins, make LOCK and 
> PROCLOCK fixed-size, and change the default to 
> max_locks_per_transaction=128. I will do one final self-review of the 
> remaining earlier patches from this thread next; I believe they're ready 
> to be committed too.
> 
> Thanks for the review!

And committed the rest of the patches from this thread now too, after 
some small fixes and cleanups. Thanks again!

- Heikki