Service resource management: i.e. Mailman3 vs Mailman2

[Ron / BCLUG]

I found a nifty trick for measuring the resource consumption of various 
services using systemd.

This was while trying to gauge the differences between Mailman v2 and 
Mailman v3 resource management.


I have ranted about how much more expensive MM3 is in resource 
consumption (basically, about ¾ of a 2GB RAM VPS is consumed).

I wanted further details.


What I found was, a setting (or several) that systemd provides:

There are a couple methods for enabling the *Accounting= features:

Edit /etc/systemd/system.conf and enabling:
   DefaultCPUAccounting=yes
   DefaultIOAccounting=yes
   DefaultIPAccounting=yes
   DefaultBlockIOAccounting=yes
   DefaultMemoryAccounting=yes
   DefaultTasksAccounting=yes

If one wants it for a single service, also a couple methods:

systemctl set-property mailman3 TasksAccounting=yes MemoryAccounting=yes
systemctl daemon-reload

Or add these lines (my preferred method, no systemctl daemon-reload needed):

# systemctl edit mailman3

[Service]
MemoryAccounting=yes
TasksAccounting=yes


Or:
do it manually


This makes it really easy to measure resources used by a service that 
has many processes running, i.e.:

# systemctl status mailman
...
       Tasks: 9 (limit: 2256)
      Memory: 46.5M
      CGroup: /system.slice/mailman.service
              ├─1054 /usr/bin/python2 /usr/lib/mailman/bin/mailmanctl
              ├─1056 /usr/bin/python2 /var/lib/mailman/bin/qrunner
              ├─1057 /usr/bin/python2 /var/lib/mailman/bin/qrunner
              ├─1058 /usr/bin/python2 /var/lib/mailman/bin/qrunner
              ├─1067 /usr/bin/python2 /var/lib/mailman/bin/qrunner
              ├─1068 /usr/bin/python2 /var/lib/mailman/bin/qrunner
              ├─1071 /usr/bin/python2 /var/lib/mailman/bin/qrunner
              ├─1083 /usr/bin/python2 /var/lib/mailman/bin/qrunner
              └─1084 /usr/bin/python2 /var/lib/mailman/bin/qrunner

And for comparison, mailman 3 (which has TWO service files):

# systemctl status mailman3
...
       Tasks: 17
      Memory: 889.9M
      CGroup: /system.slice/mailman3.service
              ├─4112698 /opt/mailman/venv/bin/python
              ├─4112711 /opt/mailman/venv/bin/python
              ├─4112712 /opt/mailman/venv/bin/python
              ├─4112713 /opt/mailman/venv/bin/python
              ├─4112714 /opt/mailman/venv/bin/python
              ├─4112715 /opt/mailman/venv/bin/python
              ├─4112717 /opt/mailman/venv/bin/python
              ├─4112718 /opt/mailman/venv/bin/python
              ├─4112719 /opt/mailman/venv/bin/python
              ├─4112720 /opt/mailman/venv/bin/python
              ├─4112721 /opt/mailman/venv/bin/python
              ├─4112725 /opt/mailman/venv/bin/python
              ├─4112726 /opt/mailman/venv/bin/python
              ├─4112790 /opt/mailman/venv/bin/python
              └─4112791 /opt/mailman/venv/bin/python

# systemctl status mailman3-web
...
       Tasks: 12
      Memory: 182.4M
      CGroup: /system.slice/mailman3-web.service
              ├─4112890 /opt/mailman/venv/bin/uwsgi
              ├─4112904 /opt/mailman/venv/bin/uwsgi
              ├─4112905 /opt/mailman/venv/bin/uwsgi
              ├─4112906 /bin/sh ...
              ├─4112908 /opt/mailman/venv/bin/python
              ├─4112910 /opt/mailman/venv/bin/python
              ├─4112912 /opt/mailman/venv/bin/python
              ├─4112913 /opt/mailman/venv/bin/python
              ├─4112914 /opt/mailman/venv/bin/python
              └─4112915 /opt/mailman/venv/bin/python


It's now quite clear: mm2 uses 9 process and < 50 MB RAM, but MM3 uses 
17+12=29 processes (and that's with the default NNTP bridge disabled), 
and 889.9+182.4=1072.3 MB RAM.

That's a *lot* of Python processes!

Also, both require Apache (or NGINX), and MM3 requires PostgreSQL.



As it is, I can see a lot of small mailing list users abandoning MM3 
over this issue (plus its complexity).

For my list, that's about one Python interpreter loaded into RAM for 
each list subscriber!