at the end, I decided to keep old tables and create a new one instead:

MariaDB [test]> select * from information_schema.system_variables where variable_name='completion_type'\g

*************************** 1. row ***************************

        VARIABLE_NAME: COMPLETION_TYPE

        SESSION_VALUE: CHAIN

         GLOBAL_VALUE: NO_CHAIN

  GLOBAL_VALUE_ORIGIN: COMPILE-TIME

        DEFAULT_VALUE: NO_CHAIN

       VARIABLE_SCOPE: SESSION

        VARIABLE_TYPE: ENUM

     VARIABLE_COMMENT: The transaction completion type

    NUMERIC_MIN_VALUE: NULL

    NUMERIC_MAX_VALUE: NULL

   NUMERIC_BLOCK_SIZE: NULL

      ENUM_VALUE_LIST: NO_CHAIN,CHAIN,RELEASE

            READ_ONLY: NO

COMMAND_LINE_ARGUMENT: REQUIRED

1 row in set (0.00 sec)

Yes, I'll have the information about static/dynamic. But, probably, not the timestamp — this would have a rather high relative overhead (like 3x – 100x storage overhead, depending on the implementation).

Also missing if the global value is static or not.

• some variables are set on startup (so static)
• others can be changed at any time (so dynamic)
• others can be changed only when replication is stopped (slave_parallel_workers in MySQL 5.6. There may be something similar in MariaDB). Indicating variables which can only be changed (or their behaviour is picked up) "at certain points in time" would also be useful.

Perhaps, adding a time of last_update would be useful. I've seen already with P_S that having the stats is great but if you don't know how long they have been configured that way it might be an issue. So perhaps an extra column of the form:

last_change TIMESTAMP NOT NULL DEFAULT CURRENT_TIMESTAMP (or "boot time"...) might be useful.

When doing this, we should also show the following:

• Default value
• How the value was set. One of
• Default value, Set-by-config-file, Set-by-user, auto-configured (ie, tunned by the server depending on other values)

if we extend existing I_S tables, then we can at the same time extend I_S.PLUGIN and I_S.COLLATION to show usage counters (that now only feedback plugin can show). In this case the better name for the old mode would be something like OLD_I_S_TABLES