"
It is well known that seastar applications, like Scylla, do not play
well with external processes: CPU usage from external processes may
confuse the I/O and CPU schedulers and create stalls.
We have also recently seen that memory usage from other application's
anonymous and page cache memory can bring the system to OOM.
Linux has a very good infrastructure for resource control contributed by
amazingly bright engineers in the form of cgroup controllers. This
infrastructure is exposed by SystemD in the form of slices: a
hierarchical structure to which controllers can be attached.
In true systemd way, the hierarchy is implicit in the filenames of the
slice files. a "-" symbol defines the hierarchy, so the files that this
patch presents, scylla-server and scylla-helper, essentially create a
"scylla" cgroup at the top level with "server" and "helper" children.
Later we mark the Services needed to run scylla as belonging to one
or the other through the Slice= directive.
Scylla DBAs can benefit from this setup by using the systemd-run
utility to fire ad-hoc commands.
Let's say for example that someone wants to hypothetically run a backup
and transfer files to an external object store like S3, making sure that
the amount of page cache used won't create swap pressure leading to
database timeouts.
One can then run something like:
sudo systemd-run --uid=id -u scylla --gid=id -g scylla -t --slice=scylla-helper.slice /path/to/my/magical_backup_tool
(or even better, the backup tool can itself be a systemd timer)
"
* 'slices' of https://github.com/glommer/scylla:
systemd: put scylla processes in systemd slices.
move postinst steps to an external script
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