Re: Tuned service on Linux

On Sun, 2024-02-11 at 16:26 +0100, Martin Berger wrote:
> Hi Mladen, 
>
> I checked file /usr/lib/tuned/oracle/tuned.conf On my system it contains 
> #
> # tuned configuration
> #
>
> [main]
> summary=Optimize for Oracle RDBMS
> include=throughput-performance
>
> [sysctl]
> vm.swappiness = 10
> vm.dirty_background_ratio = 3
> vm.dirty_ratio = 40
> vm.dirty_expire_centisecs = 500
> vm.dirty_writeback_centisecs = 100
> kernel.shmmax = 4398046511104
> kernel.shmall = 1073741824
> kernel.shmmni = 4096
> kernel.sem = 250 32000 100 128
> fs.file-max = 6815744
> fs.aio-max-nr = 1048576
> net.ipv4.ip_local_port_range = 9000 65499
> net.core.rmem_default = 262144
> net.core.rmem_max = 4194304
> net.core.wmem_default = 262144
> net.core.wmem_max = 1048576
> kernel.panic_on_oops = 1
> kernel.numa_balancing = 0
>
> [vm]
> transparent_hugepages=never
>
> For a full overview you also have to check the throughput-
> performance configuration. 
>
> I would not care so much about the dirty_* parameters - as long as my
> Instances use direct-IO. 
> Swappiness is a religious discussion: I prefer to have sufficient memory
> so swap does never (significantly) occur, but I accept other messages of
> salvation. 
> shmmni can be a problem for very large systems - the alert.log will tell
> you (assuming hugepages are used)  
> numa_balancing  will not make any difference until you have huge server
> with high variance in NUMA distances). Then it might depend how you use
> this system (one single SGA, multiple independent instances, ...) and it
> might require cgroups or other methods to do a specific NUMA
> configuration.  
>
> Personally I don't expect any harm but also no significant gain. vm.
> settings will not gain a lot, kernel.memory settings are ok, if they are
> not you will see at instance startup. 
>  
> hth, 
>  Martin 

Thanks Martin, 
I have the same file. It looks like the "oracle" profile applies Red Hat recommendation for writing out the modified ("dirty") pages. Basically, Red Hat recommends dirty pages to be written out as soon as they're modified, so that I/O is spread over time and that there aren't any spikes when the database crunch time hits. However, if the SGA is sized correctly, there shouldn't be much of paging activity anyway, so that recommendation doesn't really matter.
Furthermore, I am not really sure what does the "tuned" service do? Does it blindly change the values, based on the profile definition, or does it do some intelligent analysis? Based on the /var/log/tuned/tuned.log, I would say it simply overrides the values defined in /etc/sysctl.conf with the new values. In plain English, that means that tuned undoes the careful tuning of /etc/sysctl.conf with some magic values recommended by Red Hat. Here is the snippet from tuned.log that made me conclude this:

2024-02-11 10:06:29,519 INFO tuned.plugins.plugin_sysctl: reapplying system sysctl
2024-02-11 10:06:29,530 INFO tuned.plugins.plugin_sysctl: Overriding sysctl parameter 'vm.dirty_background_ratio' from '10' to '5' 2024-02-11 10:06:29,530 INFO tuned.plugins.plugin_sysctl: Overriding sysctl parameter 'vm.dirty_ratio' from '40' to '10' 2024-02-11 10:06:29,543 INFO tuned.plugins.plugin_sysctl: Overriding sysctl parameter 'vm.dirty_background_ratio' from '10' to '5' 2024-02-11 10:06:29,543 INFO tuned.plugins.plugin_sysctl: Overriding sysctl parameter 'vm.dirty_ratio' from '40' to '10' 2024-02-11 10:06:29,543 INFO tuned.daemon.daemon: static tuning from profile  'throughput-performance' applied
2024-02-11 10:06:39,548 INFO tuned.plugins.plugin_cpu: setting new cpu laten cy 100

2024-02-11 10:06:59,475 INFO     tuned.daemon.controller: terminating controller
2024-02-11 10:06:59,475 INFO     tuned.daemon.daemon: stopping tuning
2024-02-11 10:06:59,486 INFO     tuned.daemon.daemon: terminating TuneD, rolling

And I confirmed that the changed parameters are in effect:

gogala_at_umajor:/proc/sys/vm$ cat dirty_ratio 10
mgogala_at_umajor:

So, it looks like this "tuned" thingy is just another mechanism for altering the sysctl.conf parameters. In other words, "tuned" is probably unnecessary.

-- 
Mladen Gogala
Database SME
https://dbwhisperer.wordpress.com


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