Cloudron v9: huge disk I/O is this normal/safe/needed?

[robi]

@imc67 Holding that limiting belief is keeping your problem unresolved, no?

Sure, then trace it from the MySQL side, find which user, which container and so on..

Yes, it has everything to do with the Apps that are using that DB instance.

[james]

Hello @imc67
You can use the PID from the process to figure out what mysql service it is.

e.g. your iotop shows for mysqld the pid 1994756.
You can run systemctl status mysql.service and there is the pid displayed:

● mysql.service - MySQL Community Server
     Loaded: loaded (/usr/lib/systemd/system/mysql.service; enabled; preset: enabled)
     Active: active (running) since Mon 2025-12-01 09:17:59 UTC; 1 week 5 days ago
   Main PID: 1994756 (mysqld)
     Status: "Server is operational"
      Tasks: 48 (limit: 4603)
     Memory: 178.7M (peak: 298.0M swap: 95.4M swap peak: 108.7M)
        CPU: 1h 41min 31.520s
     CGroup: /system.slice/mysql.service
             └─1994756 /usr/sbin/mysqld

Notice: journal has been rotated since unit was started, output may be incomplete.

So from iotop I can confirm that the system mysqld service is pid 1994756 so I'd know to inspect the system mysqld service and not the docker mysql service.

You can also get the pid from the mysqld inside the docker container with docker top mysql:

docker top mysql
UID                 PID                 PPID                C                   STIME               TTY                 TIME                CMD
root                1889                1512                0                   Nov07               ?                   00:06:17            /usr/bin/python3 /usr/bin/supervisord --configuration /etc/supervisor/supervisord.conf --nodaemon -i Mysql
usbmux              3079                1889                0                   Nov07               ?                   03:49:38            /usr/sbin/mysqld
usbmux              3099                1889                0                   Nov07               ?                   00:00:11            node /app/code/service.js

Then I know the mysqld pid of the docker service is 3079 which I can check again with the system:

ps uax | grep -i 3079
usbmux      3079  0.4  1.0 1587720 43692 ?       Sl   Nov07 229:38 /usr/sbin/mysqld

Now we can differentiate between the two.

---

Okay.
Now that we can differentiate between the two, you can observe iotop and see which one has a high I/O.
After you narrow it down to either one, then we can do some analysis what database / table get accesses the most even further narrow it down.

[imc67]

Ok, thanks for your hints!!

The result was PID 19974

However:

● mysql.service - MySQL Community Server
     Loaded: loaded (/lib/systemd/system/mysql.service; enabled; vendor preset: enabled)
     Active: active (running) since Sat 2025-12-13 05:57:30 UTC; 1 day 5h ago
    Process: 874 ExecStartPre=/usr/share/mysql/mysql-systemd-start pre (code=exited, status=0/SUCCESS)
   Main PID: 910 (mysqld)
     Status: "Server is operational"
      Tasks: 47 (limit: 77023)
     Memory: 601.7M
        CPU: 59min 14.538s
     CGroup: /system.slice/mysql.service
             └─910 /usr/sbin/mysqld

And docker top mysql

UID                 PID                 PPID                C                   STIME               TTY                 TIME                CMD
root                9842                8908                0                   Dec13               ?                   00:00:17            /usr/bin/python3 /usr/bin/supervisord --configuration /etc/supervisor/supervisord.conf --nodaemon -i Mysql
message+            19974               9842                6                   Dec13               ?                   01:56:43            /usr/sbin/mysqld
message+            19976               9842                0                   Dec13               ?                   00:01:31            node /app/code/service.js

So ps uax | grep -i 19974 gives:

message+   19974  6.6  1.8 4249604 1229136 ?     Sl   Dec13 116:48 /usr/sbin/mysqld

So at least we now know that it's the Docker MySQL

[james]

Hello @imc67
Now we can start analysing.
Edit the file /home/yellowtent/platformdata/mysql/custom.cnf and add the following lines:

[mysqld]
general_log = 1
slow_query_log = 1

Restart the MySQL service in the Cloudron Dashboard.
The log files are stored at /home/yellowtent/platformdata/mysql/mysql.log and /home/yellowtent/platformdata/mysql/mysql-slow.log.

Let it run for a day or more.
Then you can download the log files and see what queries run very often causing disk I/O.

[imc67]

I enabled this en within seconds the log file was enormous, I asked ChatGPT to analyse it and here is it's observations: (too technical for me):

---

Some observations after briefly enabling the MySQL general log (Cloudron v9)

I enabled the MySQL general log only for a short time because of disk I/O concerns, but even within a few minutes a clear pattern showed up.

What I’m seeing:

• A very high number of
  INSERT INTO session (...) and
  INSERT ... ON DUPLICATE KEY UPDATE
• These happen continuously and come from 172.18.0.1
• As far as I understand, this IP is the Docker bridge gateway in Cloudron, so it likely represents multiple apps

I temporarily disabled Matomo to rule that out, but disk I/O and session-related writes did not noticeably decrease, so it does not seem to be the main contributor.

From the log it looks like:

• Multiple applications are storing sessions in MySQL
• Session rows are updated on almost every request
• This can generate a lot of InnoDB redo log and disk I/O, even with low traffic

Nothing looks obviously broken, but I’m trying to understand whether this level of session write activity is:

• expected behavior in Cloudron v9
• something that can be tuned or configured
• or if there are recommended best practices (e.g. Redis for sessions)

Any guidance on how Cloudron expects apps to handle sessions, or how to reduce unnecessary MySQL write I/O, would be much appreciated.

Thanks for looking into this.

[joseph]

Do you have happen to use nextcloud on the server? I think nextcloud+ldap keeps doing a login request when syncing for each file (which might trigger a login eventlog in mysql)

[imc67]

@joseph said in Cloudron v9: huge disk I/O is this normal/safe/needed?:

Do you have happen to use nextcloud on the server? I think nextcloud+ldap keeps doing a login request when syncing for each file (which might trigger a login eventlog in mysql)

No there is no Nextcloud on this server