SET @start_global_value = @@global.XENGINE_DATADIR;
SELECT @start_global_value;
@start_global_value
./.xengine
"Trying to set variable @@global.XENGINE_DATADIR to 444. It should fail because it is readonly."
SET @@global.XENGINE_DATADIR   = 444;
ERROR HY000: Variable 'xengine_datadir' is a read only variable