On Thu, Apr 2, 2026 at 10:15 PM Heikki Linnakangas <[email protected]> wrote: > > On 02/04/2026 19:13, Ashutosh Bapat wrote: > > On Thu, Apr 2, 2026 at 7:44 PM Heikki Linnakangas <[email protected]> wrote: > >> > >>> I think we should highlight the change in default in the release notes > >>> though. The users which use default configuration will notice an > >>> increase in the memory. If they are using a custom value, they will > >>> think of bumping it up. Can we give them some ballpark % by which they > >>> should increase their max_locks_per_transaction? E.g. double the > >>> number or something? > >> > >> I don't think people who are using the defaults will notice. I'm worried > >> about the people who have set max_locks_per_transactions manually, and > >> now effectively get less lock space for the same setting. Yeah, doubling > >> the previous value is a good rule of thumb. > > > > Users who have set max_locks_per_transaction to a non-default value > > but have tuned their application to respect those limits are safe even > > after this change, since their lock hash table never used wiggle room. > > Those users who weren't careful to respect those limits will need to > > bump their setting. > > That's technically true, but in practice it's very hard for someone to > carefully tune the setting. It's difficult to know how many locks a > particular set of queries take. In practice what people do is they bump > up the setting if the get the "out of shared memory" error, until the > error goes away. If you do the tuning that way, it's quite possible that > you are relying the "wiggle room" without realizing it. >
That's true. > > 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. -- Best Wishes, Ashutosh Bapat
