how to get the current value of a variable in the CLI?

[Kenji]

in the clickhouse-client I can set value like this:

SET max_threads = 4;

What's the opposite operation? How do I get the current value?  My question is not specific to max_threads.  It's just an example.

[Nitesh Chaudhary]

I don't remember the exact parameter name but this works:

You can get the current value by running the query  in system table:

select * from system.settings where name like '%thread%'

One of the parameters are gonna be max_thread which usually have auto value of the number of cores in your system.

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[Nitesh Chaudhary]

++ Usually the user related parameters are +nt in system.settings table.

[Kenji]

That worked great.

I confirmed the system.settings are per session e.g. SET max_threads=4 in a session doesn't affect another clickhouse-client session.

I also learned that "SET" is meant for settings only.  Therefore the name must exist in the system.settings.

Thank you.

[Denis Zhuravlev]

There are custom settings as well. Starting from release v20.8.2.3-stable, 2020-09-08

SET custom_a = 123;

SELECT getSetting('custom_a');

https://clickhouse.tech/docs/en/operations/settings/#custom_settings

[Denis Zhuravlev]

SELECT getSetting('max_threads')

┌─getSetting('max_threads')─┐
│                         8 │
└───────────────────────────┘

[Kenji]

The getSetting function is neat.
Thanks for the custom settings, too. It will come in handy!

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