select @@global.relay_log_index;
@@global.relay_log_index
NULL
select @@session.relay_log_index;
ERROR HY000: Variable 'relay_log_index' is a GLOBAL variable
show global variables like 'relay_log_index';
Variable_name	Value
relay_log_index	
show session variables like 'relay_log_index';
Variable_name	Value
relay_log_index	
select * from information_schema.global_variables where variable_name='relay_log_index';
VARIABLE_NAME	VARIABLE_VALUE
RELAY_LOG_INDEX	
select * from information_schema.session_variables where variable_name='relay_log_index';
VARIABLE_NAME	VARIABLE_VALUE
RELAY_LOG_INDEX	
set global relay_log_index=1;
ERROR HY000: Variable 'relay_log_index' is a read only variable
set session relay_log_index=1;
ERROR HY000: Variable 'relay_log_index' is a read only variable