Add support for Type=notify-reload with systemd

[tie]

This PR adds support for using pgbouncer with Type=notify-reload systemd service.

See https://www.freedesktop.org/software/systemd/man/latest/sd_notify.html

Note that Type=notify-reload services do not need ExecReload= command and use ReloadSignal= that conveniently defaults to SIGHUP.

[eulerto]

I'm afraid we cannot accept this PR. This service type (notify-reload) was added in version 253. There are still supported operating systems that use old systemd versions like Ubuntu focal (245), Ubuntu jammy (249), Rocky 8 (239) and Rocky 9 (252). Once the main distributions support this feature we can merge this PR.

[tie]

@eulerto, sorry, I don’t understand your concerns. This PR makes a single change that could be incompatible with older systemd versions, that is, updates Type= in etc/pgbouncer.service. If some distributions use the provided example unit as-is, we can document that pgbouncer supports Type=notify-reload in the comment above instead and update it later. sd_notifyf has been available for decades and Type=notify should simply ignore unknown fields like MONOTONIC_USEC.

[tie]

etc/pgbouncer.service

And from what I understand, this file is used for reference/documentation purposes only. That is, it is installed under docdir and distributions ship their own service definitions, e.g.

• Debian latest: https://salsa.debian.org/postgresql/pgbouncer/-/blob/460febb15ab9f040e74da9b2d4023fe3bb5c8481/debian/pgbouncer.service
• (Ubuntu package is mostly derived from Debian)
• Ubuntu (focal): https://git.launchpad.net/ubuntu/+source/pgbouncer/tree/debian?h=applied/ubuntu/focal
• Ubuntu (jammy): https://git.launchpad.net/ubuntu/+source/pgbouncer/tree/debian?h=applied/ubuntu/jammy
• Not sure where Rocky Linux code is hosted.

[JelteF]

I think the sd_notifyf call should be fine to merge. Assuming that it indeed does not break older systemd setups.

But I do agree with @eulerto and the default systemd config which people copy paste should work with at least the majority of systems that people are expected to run in production environments. Since both the latest RHEL and latest Ubuntu LTS don't even support this feature, currently is not the time for that.

I'd be okay with merging a change to the comments of the config file, mentioning what could be change for systemd 253+. So basically inverting the comment addition that you made.

[JelteF]

To be clear, I do agree that most people will use the systemd file from their package management. But even that being the case, showing a systemd file in the docs that is broken for pretty much all systems that we expect people to run at the moment seems like a bad choice.

[tie]

@JelteF, rebased and inverted the comment. I’ve also noticed that I’ve wrongly assumed that get_cached_time/get_time_usec from libusual uses CLOCK_MONOTONIC that is required for proper reload synchronization with systemd (currently get_time_usec uses gettimeofday. I’ve added explicit clock_gettime call in this PR.

[eulerto]

My main objection is related to the pgbouncer.service modification. It is just a comment, I'm fine.

[eulerto]

LGTM