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Description
Supporting socket activation would make each of the following possible for admins:
- Cleaner restarts (the listener socket stays open persistently)
- Network namespace isolation, disallowing any network access beyond the inherited listener port (and connections accepted from it).
- Lazy startup for densely hosted instances. (It's also possible with socket activation to start it eagerly, as usual.)
- Running MariaDB on privileged ports without having to start it initially as root
- Non-racy startup for services (like a PHP site) that depend on connecting to MariaDB. Because systemd opens listener sockets early in boot, they're available even while MariaDB is starting
- Deeper integration into coming network support in future systemd releases
Some examples in C are here:
http://0pointer.de/blog/projects/socket-activation.html
I am willing to sponsor development of this feature.
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MDEV-4606 cmake build to be able to choose sysvinit or systemd (or other) init files
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If you have two ListenStream= options, systemd will send in two separate socket file descriptors. Is that handled in the code?
Actually 3 since the unix socket is a ListenStream too. Up to 10 are handled within the code which is just a #define with non-fatal errors if this is exceeded and written to mysql error log.
Reminded me the current code has extra_ip_sock(extra-port) has special handling. How important is it to maintain this?
if (mysql_socket_getfd(sock) == mysql_socket_getfd(extra_ip_sock))
{
thd->extra_port= 1;
thd->scheduler= extra_thread_scheduler;
}
Reminded me the current code has extra_ip_sock(extra-port) has special handling. How important is it to maintain this?
I've never been a fan of the specialized handling of the IP versus the Unix socket. It would be great to have a generic pool of listeners; I see no downside.
More fixes. I dare say this is getting pretty close.
Using systemd list fds on ip_sock, extra_ip_sock and unix_socket wasn't working as there needed to be a determination of the socket type. As systemd can specify multiple sockets in any order a proper map of socket type to file descriptor was made.
The performance schema interface was also missing which is now corrected. For the moment I've put a PS event type for systemd_unix, systemd_ipv6, systemd_ipv4 but can probably expand these to include path/host/port/numbers information if desired. Although the code for HAVE_POLL=no is there I couldn't get past MDEV-7473 which stalled on linux even with -DHAVE_SYSTEMD=no -DHAVE_POLL=no but hey, linux always has poll and systemd isn't ported to non-linux so we're safe for now.
The socket activation part already implements MDEV-6536 IPv6 bind address now because systemd handles the opening of sockets and with a little more config parsing some of these new structures this sets the basis a more extensive listening interface.
The main missing bit so far, a decent automated test case. Nothing non-root exists in systemd however it shouldn't be too hard to open a few sockets, set some env vars and exec another process.
Added https://github.com/MariaDB/server/pull/83 to merge to 10.1 incorporating review comments
Just for anybody who is not willing to read the whole passionate discussion at (1), I'd like to point out the comment #62 there (2), which summarizes the main cons of using socket activation for a database server. I'd also add another comment, that according at least Fedora guidelines, socket-activated services need to be autostart (3), which is not something we wish from database server, and worth noting that other distros can have similar requirements.
That having in mind, I don't think it's worth trying to implement socket activation now, unless there is some special use case for such a feature.
(1) https://bugzilla.redhat.com/show_bug.cgi?id=714426
(2) https://bugzilla.redhat.com/show_bug.cgi?id=714426#c62
(3) https://fedoraproject.org/wiki/Packaging:Systemd#Socket_activation