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AWS engineer reports PostgreSQL perf halved by Linux 7.0, fix may not be easy

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Re: AWS engineer reports PostgreSQL perf halved by Linux 7.0, fix may not be easy

#11

Post by perching_aix »

FireBeyond wrote: post #3

Once upon a time, Linus would shout and yell about how the kernel should never "break" userspace (and I see in some places, some arguments of "It's not broken, it's just a performance regression" - personally I'd argue a 50% hit to performance of a pre-eminent database engine is ... quite the regression). Now, the kernel engineer who introduced the brand new mechanism (introduced in Linux 7.0) for handling pre-emptio…

Entertaining perspective - I thought that the whole "it's not an outage it's a (horizontal or vertical) degradation" thing was exclusive to web services, but thinking about it, I guess it does apply even in cases like this.

Re: AWS engineer reports PostgreSQL perf halved by Linux 7.0, fix may not be easy

#12

Post by bombcar »

jeffbee wrote: post #7
lfittl wrote: post #2

Its worth reading this follow-up LKML post by Andres Freund (who works on Postgres): https://lore.kernel.org/lkml/yr3inlzesdb45n6i6lpbimwr7b25kqk...

Funny how "use hugepages" is right there on the table and 99% of users ignore it.

I’m absolutely flabbergasted by the performance left on the table; even by myself - just yesterday I learned Gentoo’s emerge can use git and be a billion times faster.

Re: AWS engineer reports PostgreSQL perf halved by Linux 7.0, fix may not be easy

#13

Post by Neywiny »

Meekro wrote: post #8
dsr_ wrote: post #4

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 t…

> 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.

Re: AWS engineer reports PostgreSQL perf halved by Linux 7.0, fix may not be easy

#14

Post by stingraycharles »

Neywiny wrote: post #13
Meekro wrote: post #8

Earlier quoted context omitted.

> 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.

Re: AWS engineer reports PostgreSQL perf halved by Linux 7.0, fix may not be easy

#17

Post by bombcar »

dsr_ wrote: post #4

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 t…

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

Re: AWS engineer reports PostgreSQL perf halved by Linux 7.0, fix may not be easy

#19

Post by TacticalCoder »

lfittl wrote: post #2

Its worth reading this follow-up LKML post by Andres Freund (who works on Postgres): https://lore.kernel.org/lkml/yr3inlzesdb45n6i6lpbimwr7b25kqk...

AIUI in that thread they're saying "0.51x" the perf on a 96-core arm64 machine and they're also saying they cannot reproduce it on a 96-core amd64 machine.

So it's not going to affect everybody both running PostgreSQL and upgrading to the latest kernel. Conditions seems to be: arm64, shitloads of core, kernel 7.0, current version of PostgreSQL.

That is not going to be 100% of the installed PostgreSQL DBs out there in the wild when 7.0 lands in a few weeks.

Re: AWS engineer reports PostgreSQL perf halved by Linux 7.0, fix may not be easy

#20

Post by bombcar »

stingraycharles wrote: post #6
dsr_ wrote: post #4

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 t…

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.

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