I played around with my local config.xml file. The minimal working example is this:
<?xml version="1.0"?>
<clickhouse>
<mark_cache_size>5368709120</mark_cache_size>
<listen_host>localhost</listen_host>
<tcp_port>9000</tcp_port>
<users_config>users.xml</users_config>
<logger><console>true</console></logger>
</clickhouse>
Not specifying mark_cache_size made the server not start up:
2022.05.18 12:15:06.549078 [ 8728320 ] {} <Error> Application: Not found: mark_cache_size
Looking at ClickHouse's ca. 100 server configuration options +
sub-options, it seems that mark_cache_size is NOT special enough to
require explicit configuration but instead that the behavior was
unintended because no default value was provided.
If you will execute 'SYSTEM RELOAD CONFIG' via, i.e., TCP protocol, then
reload on port change will endlessly wait for connection from which this
query had been issued, and you will see the following message in the
logs:
2022.04.28 03:34:57.552513 [ 37101 ] {b41d855c-4dbf-470a-a144-c6ae5a1abda8} <Debug> executeQuery: (from 127.0.0.1:11774) system reload config
...
2022.04.28 03:34:57.710640 [ 37101 ] {b41d855c-4dbf-470a-a144-c6ae5a1abda8} <Information> Application: Stopped listening for http://127.0.0.1:18123
2022.04.28 03:34:57.798774 [ 37101 ] {b41d855c-4dbf-470a-a144-c6ae5a1abda8} <Information> Application: Stopped listening for native protocol (tcp): 127.0.0.1:19000
...
2022.04.28 03:34:57.901375 [ 37101 ] {b41d855c-4dbf-470a-a144-c6ae5a1abda8} <Debug> Application: Server finished: http://127.0.0.1:18123
2022.04.28 03:34:57.901455 [ 37101 ] {b41d855c-4dbf-470a-a144-c6ae5a1abda8} <Trace> Application: Waiting server to finish: native protocol (tcp): 127.0.0.1:19000
2022.04.28 03:34:58.001717 [ 37101 ] {b41d855c-4dbf-470a-a144-c6ae5a1abda8} <Trace> Application: Waiting server to finish: native protocol (tcp): 127.0.0.1:19000
2022.04.28 03:34:58.101881 [ 37101 ] {b41d855c-4dbf-470a-a144-c6ae5a1abda8} <Trace> Application: Waiting server to finish: native protocol (tcp): 127.0.0.1:19000
...
2022.04.28 03:35:01.707951 [ 37101 ] {b41d855c-4dbf-470a-a144-c6ae5a1abda8} <Trace> Application: Waiting server to finish: native protocol (tcp): 127.0.0.1:19000
But waiting for the current connection will never ends.
So instead of waiting directly from the query context (SYSTEM RELOAD
CONFIG) do this in background (actually not even in background, but
check on server reload and on exit).
v0: just don't wait for the servers
v2: fix use-after-free by removing dependency from server in handlers
v3: wait servers in background to avoid use-after-free of the context
Signed-off-by: Azat Khuzhin <a.khuzhin@semrush.com>
