Why are journal files stored in machine-specific directories?

[Jakub Piecuch <j.piecuch96@xxxxxxxxx>]

Hello,

I'm wondering why journald stores journal files under
/var/log/journal/$MACHINE_ID instead of just /var/log/journal.

I found the commit that introduces this change, but it contains
no justification:
https://github.com/systemd/systemd/commit/ed49ef3f349bcd4f0483ba8254a2537fe8e9cd17

I also searched the systemd-devel mailing list archive, but didn't find
anything.

I know that journal namespaces are a thing, but the namespaces share the same
machine id, so I don't think they are the reason for it. I also think that
journal namespaces came quite some time after the commit mentioned above.

Does anyone have some insights they are willing to share?

Thanks,
Jakub