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From: Hannu Krosing <[email protected]>
To: Andres Freund <[email protected]>
Cc: Jonathan S. Katz <[email protected]>
Cc: Heikki Linnakangas <[email protected]>
Cc: Tom Lane <[email protected]>
Cc: pgsql-hackers <[email protected]>
Subject: Re: Let's make PostgreSQL multi-threaded
Date: Thu, 8 Jun 2023 12:15:58 +0200
Message-ID: <CAMT0RQR1kAEhHmiy2SfhqbDvoq3mrezcENM=3vozL5cpkNDPOA@mail.gmail.com> (raw)
In-Reply-To: <CAMT0RQTAFrx5xVJ9SXyjP71=SmU+U9+4dDm+XEZWWoy6pbCF5g@mail.gmail.com>
References: <[email protected]>
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	<CAMT0RQTAFrx5xVJ9SXyjP71=SmU+U9+4dDm+XEZWWoy6pbCF5g@mail.gmail.com>

On Thu, Jun 8, 2023 at 11:54 AM Hannu Krosing <[email protected]> wrote:
>
> On Wed, Jun 7, 2023 at 11:37 PM Andres Freund <[email protected]> wrote:
> >
> > Hi,
> >
> > On 2023-06-05 13:40:13 -0400, Jonathan S. Katz wrote:
> > > 2. While I wouldn't want to necessarily discourage a moonshot effort, I
> > > would ask if developer time could be better spent on tackling some of the
> > > other problems around vertical scalability? Per some PGCon discussions,
> > > there's still room for improvement in how PostgreSQL can best utilize
> > > resources available very large "commodity" machines (a 448-core / 24TB RAM
> > > instance comes to mind).
> >
> > I think we're starting to hit quite a few limits related to the process model,
> > particularly on bigger machines. The overhead of cross-process context
> > switches is inherently higher than switching between threads in the same
> > process - and my suspicion is that that overhead will continue to
> > increase. Once you have a significant number of connections we end up spending
> > a *lot* of time in TLB misses, and that's inherent to the process model,
> > because you can't share the TLB across processes.
>
>
> This part was touched in the "AMA with a Linux Kernale Hacker"
> Unconference session where he mentioned that the had proposed a
> 'mshare' syscall for this.

Also, the *static* huge pages already let you solve this problem now
by sharing the page tables


Cheers
Hannu

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