Hi Mladen,
As mentioned in my original post, yes, it is Linux.
I have no direct experience with the client system, that comes from a
colleague.
To sum it up, there seems to be no reason to continue to allocate swap on
modern Linux systems, as it really serves no good purpose.
There was a time when swap was necessary, but times have changed.
Jared Still
Certifiable Oracle DBA and Part Time Perl Evangelist
Principal Consultant at Pythian
Oracle ACE Alumni
Pythian Blog http://www.pythian.com/blog/author/still/
Github: https://github.com/jkstill
Personality: http://www.personalitypage.com/INTJ.html
On Thu, Mar 30, 2023 at 12:22 PM Mladen Gogala <gogala.mladen@xxxxxxxxx>
wrote:
On 3/30/23 13:46, Jared Still wrote:
I was recently asked by a colleague this same question.
He had been asked by a client, with a fairly well regarded sysadmin team.
They wanted to eliminate swap: here's why.
If a process is consuming memory at a prodigious rate, then the OOM (out
of memory) killer is going to catch up to it and kill it eventually.
Their position was that with a swap partition, this process was prolonged
far too long.
Without swap, the process gets killed relatively quickly.
With swap, it can take many minutes. The CPU spends so much time managing
memory on swap (remember, we are at an OOM condition), which is slow, that
the time to kill the process is prolonged to many minutes.
At first my position was "what, no swap! we can't do that!"
But, I decided to test it a bit.
A small physical server, 4 cores and 32G of RAM, is running Oracle 19.3.
A swingbench test is running, 10 sessions per core.
When I cause an OOM condition with the 16G swap partition enabled, it took
the system between 7.5-8 minutes to kill the process.
(For the client, the amount of time was 20+ minutes.)
And during that time, it was impossible to logon to the server. The CPU
was too busy thrashing around in the swap partition.
The next step of course is to disable the swap.
Same OOM condition caused. Time to resolution is now 7 seconds.
There is no swap to manage as if it were RAM.
That is quite a bit difference.
Of course I wondered 'what about paging in memory for new processes?', as
that often uses a page in swap.
Without swap, it just takes place in memory.
Swap is also a landing place for some pages used to initialize processes,
as they can only be used once.
This is a minimal amount, and can just be left in memory.
If one really wants to conserve, there is a thing called ZRAM (compressed
memory) where those pages can be parked, instead of swap.
So, does anyone see any other need for a swap partition?
It seems to have outlived its usefulness.
Jared Still
Certifiable Oracle DBA and Part Time Perl Evangelist
Principal Consultant at Pythian
Oracle ACE Alumni
Pythian Blog http://www.pythian.com/blog/author/still/
Github: https://github.com/jkstill
Personality: http://www.personalitypage.com/INTJ.html
Hi Jared,
I will assume that your operating system is Linux. Did you try limiting
the core or rss size from /etc/security/limits.conf? That should kill the
offending process as soon as the limit is hit. One note on the cheeky side:
this is the first time I see optimizing of a failure. I assume you have
isolated the process and that you know what triggers the unwanted
occurrence? How about killing the offending process with "kill -9" when it
starts misbehaving?
Regards
--
Mladen Gogala
Database Consultant
Tel: (347) 321-1217https://dbwhisperer.wordpress.com
