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Comment by dsr_ | Hacker News Reader

Nobody sensible runs the latest kernel; nobody running PG in production should be afraid of setting a non-default at either boot time or as a sysctl. So this will, most likely, be another step in building a PG database server (turn off pre-emption if your kernel is 7.0 or later and PG is pre-whatever-version).

At worst it might become a permanent part of building a PG server and a FAQ... but if it affects one thing this badly, it will affect others.

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> Nobody sensible runs the latest kernel

From the article: "Linux 7.0 stable is due out in about two weeks. This is also the kernel version powering Ubuntu 26.04 LTS to be released later in April."

Unfortunately, lots of people will be running it in less than a month. At the moment, it'll take a kernel patch (not a sysctl) to undo this-- hopefully something changes.

Not nobody but not everybody upgrades to the newest distros immediately. That's the advantage of LTS. I've even found that a lot of programs have poorer support on 24.04 than 22.04 due to security changes, so I'm fine sticking with 22.04 as my main dev system.

This seems to be brushing off a major performance regression just because you personally don’t upgrade for 4 years. I don’t think that’s common at all.

https://fr.archive.ubuntu.com/stats/stats_of_day-16.html?ver... no need to think, data backs it up

> ... not everybody upgrades to the newest distros immediately.

While that's true, for new deployments the story is often "deploy on the latest release of things available at the time".

So, there will probably be a substantial deployment of new projects / testing projects using the Linux 7.0 kernel along with the latest available software packages in a few weeks.

I would argue it's mainly inexperienced devs who deploy on the very latest. Once you get some more years under your belt you realize the value of LTS versions, even if you don't get the shiniest shiny.

> kernel version powering Ubuntu 26.04 *LTS*

Yes it’s LTS but the point is that the LTS system has overlapping support so you can wait on an older LTS for a bit before upgrading to a newer one. And it’s somewhat prudent to do so if you value stability highly, because often a few new issues will be discovered and patched after LTS goes live for a bit.

That's the advantage of LTS? 24.04 is the LTS, not the one you use, 22.04.

22.04 is also an LTS release, supported for another year still.

https://ubuntu.com/about/release-cycle

We're just now looking at moving production machines to 24.04.

If you are on a maintenance contract with Ubuntu, 22.04 is supported until 2032.

If it aint broken, don't fix it.

All even number .04 releases are LTS in Ubuntu

Someone said "its fine nobody uses this" and someone else gave the world's biggest slam dunk of "Ubuntu in 1 month" and your reply is that "not everyone does it". How far from the point can you be!

In the Linux world this is the worst possible scenario, distro with the largest adoption, LTS.

22.04 is still potentially more prevalent than 24.04 according to https://fr.archive.ubuntu.com/stats/stats_of_day-16.html?ver... . 26.04 will take some time before it's largely adopted.

Not trying to downplay the importance of this, but the LTS versions aren't until the first point release, so 26.04.1 (typically six months or so after the release).

Is that true? I haven't heard that before. Do you have a link?

Here's how they announced 24.04.0. It says LTS and doesn't mention anything about LTS coming in the .1 release: https://canonical.com/blog/canonical-releases-ubuntu-24-04-n...

I can't find any link, so I think I'm getting mixed up between what they consider LTS and when the upgrade tool starts prompting to upgrade. If you're on the 24.04 LTS, then you don't get prompted to upgrade until 26.04.1

Depends on your shop.

As someone with a heavy QA/Dev Opps background I don't think we have enough details.

Is it only ARM64 ? How many ARM64 PG DBs are running 96 cores?

However...

This is the most popular database in the world. Odds are this will effect a bunch of other lesser known applications.

Please follow the complete thread: https://lore.kernel.org/lkml/xxbnmxqhx4ntc4ztztllbhnral2adog...

> [...] used huge_pages=on - as that is the only sane thing to do with 10s to 100s of GB of shared memory [...] if I disable huge pages, I actually can reproduce the contention [...]

Thank you for sharing.

So it looks like an edge case, as usually you need huge pages at scale ??

I think most people on enterprise-y systems wait for (at least) 26.04.1, the window is 3 years (when on 24.04, which is supported until ~2029-04-30, it's 1 year when on 22.04) starting now, hardly anyone switches immediately.

Not necessarily;

``` $ grep PREEMPT_DYNAMIC /boot/config-$(uname -r) CONFIG_PREEMPT_DYNAMIC=y CONFIG_HAVE_PREEMPT_DYNAMIC=y CONFIG_HAVE_PREEMPT_DYNAMIC_CALL=y ```

if your kernel has CONFIG_PREEMPT_DYNAMIC then you can go back to the pre 7.0 default by adding preempt=none to your grub config. I haven't seen any plans by Ubuntu to drop CONFIG_PREEMPT_DYNAMIC from the default kernel config.

actually i just checked, yeah, ubuntu would have to add none back to the kernel and `CONFIG_PREEMPT_NONE=y` the config so that it can be selected at boot.

We need some sensible people running the latest and greatest or we won't catch things like this.

That may be the case, but it’s still not a great situation to be in and one has to wonder: if PostgreSQL is affected, what else is?

That's the big thing - PSQL will be tested, noticed, and fixed (and likely have a version that handles 7.0 by the time it's in common use).

But other software won't and may not even be noticed, except as a (I hate using the term) enshittification.

Better to introduce the "correct way" in 7.0 but not regress the old (translate the "correct" into the old if necessary) - and then in 8.0 or some future release implement the regression.

Exactly, this is how it’s usually done. As the developer on the mailing list mentions, implementing a new low level construct in 7.0 and a performance regression that requires said new low level construct to mitigate is not great. You need a grace period in which both old and new approach is fast.

If you're running in a docker container you share the host kernel. You might not have a choice.

The option to set PREEMPT_NONE was removed for basically all platforms.

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