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ClickHouse® is a real-time analytics DBMS
630eddbbbc
With default KillMode=control-group, systemd will send signals to all
processes in cgroup and this will lead to server will be terminated
forcefully due to double signal.
2023.09.19 12:47:06.369090 [ 763 ] {} <Information> Application: Received termination signal (Terminated)
2023.09.19 12:47:06.369141 [ 762 ] {} <Debug> Application: Received termination signal.
2023.09.19 12:47:06.369215 [ 763 ] {} <Information> Application: Received termination signal (Terminated)
2023.09.19 12:47:06.369225 [ 763 ] {} <Information> Application: This is the second termination signal. Immediately terminate.
2023.09.19 12:47:06.400959 [ 761 ] {} <Information> Application: Child process exited normally with code 143.
Someone may naively think that, hey, I can change KillMode to
process/mixed, but this will not work either, because in this case
systemd cannot wait for the $MainPID (and main_pid_alien=true in
systemd's sources), because it is not a child of systemd, and this will
lead to double signal again:
2023.09.19 16:24:19.694473 [ 3118 ] {} <Information> Application: Received termination signal (Terminated)
2023.09.19 16:24:19.694894 [ 3118 ] {} <Information> Application: Received termination signal (Terminated)
2023.09.19 16:24:19.695060 [ 3118 ] {} <Information> Application: This is the second termination signal. Immediately terminate.
And this is because it sends signal firstly on a normal termnation and
then when it cleans up left over processes:
clickhouse-server.service: Found left-over process 3117 (clickhouse-serv) in control group while starting unit. Ignoring.
And yes, even though it prints "Ignoring" here (I guess it is related to
the fact that it can be ignored if the signal will not be handled)
Here is a proof of double signal by systemd:
# pgrep clickhouse-serv | xargs strace -e /kill -fp
strace: Process 3117 attached with 469 threads
[pid 3582] --- SIGTERM {si_signo=SIGTERM, si_code=SI_USER, si_pid=1, si_uid=0} ---
[pid 3580] --- SIGCONT {si_signo=SIGCONT, si_code=SI_USER, si_pid=1, si_uid=0} ---
[pid 3582] --- SIGCONT {si_signo=SIGCONT, si_code=SI_USER, si_pid=1, si_uid=0} ---
[pid 3580] --- SIGTERM {si_signo=SIGTERM, si_code=SI_USER, si_pid=1, si_uid=0} ---
^^^
[pid 3118] tgkill(3117, 3118, SIGTERM) = 0 # and this is a force termination
So yes, there is no other way except for disabling signal forwarding.
*Well, there is another way, but I guess it is will be unwelcome (even
though systemd can be configured in multiple ways right now, and there
is even systemd-oomd instead of clickhouse'es watchdog) - disable
watchdog completelly.*
Signed-off-by: Azat Khuzhin <a.khuzhin@semrush.com>
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ClickHouse® is an open-source column-oriented database management system that allows generating analytical data reports in real-time.
How To Install (Linux, macOS, FreeBSD)
curl https://clickhouse.com/ | sh
Useful Links
- Official website has a quick high-level overview of ClickHouse on the main page.
- ClickHouse Cloud ClickHouse as a service, built by the creators and maintainers.
- Tutorial shows how to set up and query a small ClickHouse cluster.
- Documentation provides more in-depth information.
- YouTube channel has a lot of content about ClickHouse in video format.
- Slack and Telegram allow chatting with ClickHouse users in real-time.
- Blog contains various ClickHouse-related articles, as well as announcements and reports about events.
- Code Browser (Woboq) with syntax highlighting and navigation.
- Code Browser (github.dev) with syntax highlighting, powered by github.dev.
- Static Analysis (SonarCloud) proposes C++ quality improvements.
- Contacts can help to get your questions answered if there are any.
Upcoming Events
- v23.8 Community Call - Aug 31 - 23.8 is rapidly approaching. Original creator, co-founder, and CTO of ClickHouse Alexey Milovidov will walk us through the highlights of the release.
- ClickHouse & AI - A Meetup in San Francisco - Aug 8
- ClickHouse Meetup in Paris - Sep 12
Also, keep an eye out for upcoming meetups around the world. Somewhere else you want us to be? Please feel free to reach out to tyler clickhouse com.
Recent Recordings
- Recent Meetup Videos: Meetup Playlist Whenever possible recordings of the ClickHouse Community Meetups are edited and presented as individual talks. Current featuring "Modern SQL in 2023", "Fast, Concurrent, and Consistent Asynchronous INSERTS in ClickHouse", and "Full-Text Indices: Design and Experiments"
- Recording available: v23.6 Release Webinar All the features of 23.6, one convenient video! Watch it now!
- All release webinar recordings: YouTube playlist
Interested in joining ClickHouse and making it your full-time job?
We are a globally diverse and distributed team, united behind a common goal of creating industry-leading, real-time analytics. Here, you will have an opportunity to solve some of the most cutting-edge technical challenges and have direct ownership of your work and vision. If you are a contributor by nature, a thinker and a doer - we’ll definitely click!
Check out our current openings here: https://clickhouse.com/company/careers
Cant find what you are looking for, but want to let us know you are interested in joining ClickHouse? Email careers@clickhouse.com!