SET @start_global_value = @@global.rocksdb_tmpdir;
SELECT @start_global_value;
@start_global_value

select @@session.rocksdb_tmpdir;
@@session.rocksdb_tmpdir

show global variables like 'rocksdb_tmpdir';
Variable_name	Value
rocksdb_tmpdir	
show session variables like 'rocksdb_tmpdir';
Variable_name	Value
rocksdb_tmpdir	
select * from performance_schema.global_variables where variable_name='rocksdb_tmpdir';
VARIABLE_NAME	VARIABLE_VALUE
rocksdb_tmpdir	
select * from performance_schema.session_variables where variable_name='rocksdb_tmpdir';
VARIABLE_NAME	VARIABLE_VALUE
rocksdb_tmpdir	
set global rocksdb_tmpdir='value';
set session rocksdb_tmpdir='value';
set global rocksdb_tmpdir=1.1;
ERROR 42000: Incorrect argument type to variable 'rocksdb_tmpdir'
set global rocksdb_tmpdir=1e1;
ERROR 42000: Incorrect argument type to variable 'rocksdb_tmpdir'
SET @@global.rocksdb_tmpdir = @start_global_value;
SELECT @@global.rocksdb_tmpdir;
@@global.rocksdb_tmpdir

