A statement like
select if(@@hostname='box02','prod_mariadb02','n');
does not modify @@hostname. Hence the type mask should be
QUERY_TYPE_READ|QUERY_TYPE_SYSVAR_READ and NOT
QUERY_TYPE_READ|QUERY_TYPE_GSYSVAR_WRITE.
A statement like
select if(@@hostname='box02','prod_mariadb02','n');
does not modify @@hostname. Hence the type mask should be
QUERY_TYPE_READ|QUERY_TYPE_SYSVAR_READ and NOT
QUERY_TYPE_READ|QUERY_TYPE_GSYSVAR_WRITE.