On 8/19/25 17:37, Frits Hoogland wrote:
The specific issue I see in certain cases leading to unreasonable swap usage is
Linux workingset detection kicking in
Do you have a way to highlight that precisely? I mean, can you prove
that it is Linux workingset detection that is causing swapping?
Thank you for your message Frederic,
I am very much aware of that issue. It’s actually incorrect to say that is a
bug: that is how cgroupsv1, which is bundled with rhel8, works. However, it is
very counter intuitive. For that reason redhat created the
force_cgroup_v2_swappiness parameter unique
On 8/8/25 10:21, Frits Hoogland wrote:
If swappiness is set to 0, but swap is available, some documentation
suggests it will never use anonymous memory, however I found this not to
be true, linux might still choose anonymous memory to reclaim.
A bug in RHEL8 meant that swappiness was not t
available
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From: Bruce Momjian
Sent: Tuesday, August 12, 2025 1:49:26 PM
To: Frits Hoogland
Cc: Joe Conway ; Priya V ;
[email protected]
Subject: Re: Safe vm.overcommit_ratio for Large
On Wed, Aug 6, 2025 at 11:14:34PM +0200, Frits Hoogland wrote:
> > As I said, do not disable swap. You don't need a huge amount, but maybe 16
> > GB or so would do it.
>
> Joe, please, can you state a technical reason for saying this?
> All you are saying is ‘don’t do this’.
>
> I’ve stated my
Joe, I am trying to help, and make people think about things correctly.
The linux kernel is actually constantly changing, sometimes subtle and
sometimes less subtle, and there is a general lack of very clear statistics
indicating the more nuanced memory operations, and the documentation about it
On 8/6/25 17:14, Frits Hoogland wrote:
As I said, do not disable swap. You don't need a huge amount, but
maybe 16 GB or so would do it.
Joe, please, can you state a technical reason for saying this?
All you are saying is ‘don’t do this’.
I’ve stated my reasons for why this doesn’t make sense,
> As I said, do not disable swap. You don't need a huge amount, but maybe 16 GB
> or so would do it.
Joe, please, can you state a technical reason for saying this?
All you are saying is ‘don’t do this’.
I’ve stated my reasons for why this doesn’t make sense, and you don’t give any
reason.
The
(Both: please trim and reply inline on these lists as I have done;
Frits, please reply all not just to the list -- I never received your
reply to me)
On 8/6/25 11:51, Priya V wrote:
*cat /proc/sys/vm/overcommit_ratio*
50
$ *cat /proc/sys/vm/swappiness*
60
*Workload*: Multi-tenant PostgreSQL
Hi Frits, Joe,
Thank you both for you insights
*Current situation:*
*cat /proc/sys/vm/overcommit_memory*
0
*cat /proc/sys/vm/overcommit_ratio*
50
$ *cat /proc/sys/vm/swappiness*
60
*Workload*: Multi-tenant PostgreSQL
*uname -r*
4.18.0-477.83.1.el8_8.x86_64
*free -h*
total used free shared b
Joe,
Can you name any technical reason why not having swap for a database is an
actual bad idea?
Memory always is limited. Swap was invented to overcome a situation where the
(incidental) memory usage of paged in memory was could (regularly) get higher
than physical memory would allow, and th
On 8/5/25 13:01, Priya V wrote:
*Environment:*
*PostgreSQL Versions:* Mix of 13.13 and 15.12 (upgrades in progress
to be at 15.12 currently both are actively in use)
PostgreSQL 13 end of life after November 13, 2025
*OS / Kernel:* RHEL 7 & RHEL 8 variants, kernels in the 4.14–4.18
Hello Postgres community,
We operate a large PostgreSQL fleet (~15,000 databases) on dedicated Linux
hosts.
Each host runs *multiple PostgreSQL instances* (multi-instance setup, not
just multiple DBs inside one instance).
*Environment:*
-
*PostgreSQL Versions:* Mix of 13.13 and 15.12 (upg
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