Configuration of server log is not applied until restart

[currybullen]

Describe the bug
It seems configuration changes made to /etc/clickhouse-server/config.xml are not respected until clickhouse-server is restarted.

How to reproduce

• Which ClickHouse server version to use: Tried on 20.3.2.1 through 20.3.7.46
• Steps to reproduce: I found the error by changing the log level from trace to error in /etc/clickhouse-server/config.xml and issuing a simple "SELECT 1" query. Debug entries pop up in the log despite me changing the log level.

Expected behavior
The settings should update as soon as the file is changed on disk.

Additional context
I haven't tried if it works for releases between 19.16.17.80 and 20.3.7.46, but I can say it works as expected on 19.16.17.80. Looking at the output from journalctl -u clickhouse-server, it looks like the configuration is actually re-read. The post-processed file being produced under /var/lib/clickhouse/preprocessed_configs/config.xml looks right (it contains the changes made to /etc/clickhouse-server/config.xml). This is all on CentOS 7, installing ClickHouse from the official yandex RPM repo (https://repo.yandex.ru/clickhouse/rpm/stable/x86_64/)

[filimonov]

Done intentionally in v20.1.2.4, due to some race condition found during switching log files.

Require server to be restarted to apply the changes in logging configuration. This is a temporary workaround to avoid the bug where the server logs to a deleted log file (see #8696). #8707 (Alexander Kuzmenkov)

https://github.com/ClickHouse/ClickHouse/blob/master/CHANGELOG.md#backward-incompatible-change-1

@akuzm do we want to keep that issue opened as a reminder?

[akuzm]

I closed the old issue, because technically it does not reproduce anymore. We can keep this one, sure, though I don't know when we'll get to fixing it properly.