The Performance Schema provides a user_variables_by_thread table that exposes user-defined variables. These are variables defined within a specific session and include a @ character preceding the name; see Section 9.4, “User-Defined Variables”.
The user_variables_by_thread table has these columns:
THREAD_ID
The thread identifier of the session in which the variable is defined.
VARIABLE_NAME
The variable name, without the leading @ character.
VARIABLE_VALUE
The variable value.
The user_variables_by_thread table has these indexes:
Primary key on (THREAD_ID, VARIABLE_NAME)
TRUNCATE TABLE is not permitted for the user_variables_by_thread table.