> Q2) What if I decide to re-tar again my data, > should I need to invoke pg_stop_backup() first and perform pg_start_backup() -> tar -> > pg_stop_backup()?
No, that is not necessary.
I'd say that although it is not necessary, it is a good practice. As you are going to do the copy all over again, better reduce the window required for recovery. If you don't call pg_stop_backup, the restore will consider the first needed WAL file to be the one returned by the call of pg_start_backup; if this call and the tar error are not very closer in time and you have a lot of activity in the system that generated many WAL files, then the restore will require more WAL files then it is actually necessary.
Besides, if you are doing an script for this procedure, you'd better have the script handle the error and call the pg_stop_backup directly.
At last, any reason for not using pg_basebackup in this case? I'd say it is preferred over pg_start_backup+tar+pg_stop_backup, and less error prone.
