Client sessions over HTTP
Launching the ClickHouse client automatically creates a persistent session for you to send consecutive queries. But how do you do this when using the ClickHouse HTTP endpoint?
The HTTP endpoint accepts a query parameter called
session_id. The value of this parameter can be anything, it is up to you to pick a unique String as the value to use as your session ID. So you might pick something like
session_id=this_is_my_super_unique_session_id, just try to pick something that won't clash with anyone else's session ID.
$ echo "SET max_execution_time=0.5" | curl 'http://localhost:8123/?session_id=this_is_my_super_unique_session_id&session_timeout=600' --data-binary @-
To submit another query to the same session, just include the same
session_id in the next call.
$ echo "Select max(number) from system.numbers" | curl 'http://localhost:8123/?session_id=this_is_my_super_unique_session_id' --data-binary @-
It can also be good practice to add
session_check=1 as an option to subsequent calls. This checks that the session exists, and returns an error if it does not. This is useful as sessions can be killed by timeouts or server restarts, and you might want to know if session settings have been lost.
$ echo "Select max(number) from system.numbers" | curl 'http://localhost:8123/?session_id=this_is_my_super_unique_session_id&session_check=1' --data-binary @-
Code: 159. DB::Exception: Timeout exceeded: elapsed 0.500299438 seconds, maximum: 0.5. (TIMEOUT_EXCEEDED) (version 220.127.116.11)