Do I have to stop hive service before making the backup
if so, Why I have to stop it ?
if not, does that make a trouble for hive?
In case of any service which is keep on writing into the database on various tables, it is better to stop those services first before taking the Database dump. Else it might be possible that due to continuous update (DML queries) the DB dump might get into some inconsistent state Or there might be some very useful queries getting executed inside your DB while you were collecting the DB dump which might not get captured completely inside the Dump.
So better to stop the services before taking the DB dump as a best practice. However if you can take risk then it is also possible to take the DB dump in running mode of the services.