QUERY_RESPONSE_TIME_SESSION_STATS is a non-standard way to imitate global+session scope of QUERY_RESPONSE_TIME_STATS

MDEV-33501 adds a new variable QUERY_RESPONSE_TIME_SESSION_STATS.

If I understand the description correctly, it can be set to ON or OFF for the session, in which case it will work accordingly, regardless of QUERY_RESPONSE_TIME_STATS; or it can be set to GLOBAL in which case QUERY_RESPONSE_TIME_STATS will control whether the stats are collected or not.

If this is correct, I see no purpose to have the variable. It is a behavior of a standard session+global variable of which we have plenty in the server: if @@session.xxx is set to ON and OFF, it works accordingly, and if it is set to DEFAULT, the value of @@global.xxx is used.

So, instead of adding a new variable, the scope of QUERY_RESPONSE_TIME_STATS should be extended to make it both session and global.

If there is a reason why it cannot be done so, please elaborate for the documentation purposes why the new variable is needed, and move the ticket to documentation.