RMAN backup tag question

Question

I am little confused even after I read the RMAN doc. If I have a full level 0 backup tag "mybk$level_0" database, then my level 1 incremental backup tag has to be the same - "mybk$level_1" or "mybk$level_0".
I just run the incremental backup through the whole weekend and noticed the each run would generated two identical "spfile, controlefile" backup, one before the archivelog backup, one after it. Why?

Answer 1

The tag name can be the same as what you set. Tag names can be of different names and different formats, does not need to be a specific name. You can replace mybk with myarchive if you think that is more meaningful. You can also attach date and time variable with the tags to make them more meaning full.
It doesn't have to be this way,
{ backup incremental level 1 cumulative device type disk tag 'mybk%LEVEL_1' database;
recover copy of database;
backup device type disk tag 'mrarchive' archivelog all not backed up; }
If you are calling the rman backup from shell script you can attach the dates to tags as below.
export TDATE=`date +%a%m%d%y`
tag="Archive_${TDATE}"
or
tag "Archive_${TDATE}"
Below note if from one of the online resources available:
Tags for Backups and Image CopiesYou can assign a user-specified character string called a tag to backup sets and image copies (either copies created by RMAN or copies created by an operating system utility). A tag is a case-insensitive symbolic name for a backup set or file copy such as weekly_backup. You can specify the tag rather than the filename when executing the RESTORE or CHANGE command. The maximum length of a tag is 30 characters.
If you do not specify a tag name, then by default RMAN creates a tag for backups and copies (except for control file autobackups) in the format TAGYYYYMMDDTHHMMSS, where YYYY is the year, MM is the month, DD is the day, HH is the hour (in 24-hour format), MM is the minutes, and SS is the seconds. For example, a backup of datafile 1 may receive the tag TAG20020208T133437. The date and time refer to when RMAN started the backup. If multiple backup sets are created by one BACKUP command, then each backup piece is assigned the same default tag.
When applied to a backup set, a tag applies to a specific copy of the backup set. If you do not duplex a backup set, that is, make multiple identical copies of it, then a one-to-one correspondence exists between the tag and the backup set. For example, BACKUP COPIES 1 DATAFILE 7 TAG foo creates one backup set with tag foo. However, you can back up this backup set and give this new copy of the backup set the tag bar. So, the backup set has two identical copies: one tagged foo and the other tagged bar.
Tags do not need to be unique, so multiple backup sets or image copies can have the same tag name, for example, weekly_backup. When a tag is not unique, then with respect to a given datafile, the tag refers to the most current suitable file. By default, RMAN selects the most recent backups to restore unless qualified by a tag or a SET UNTIL command. The most current suitable backup containing the specified file may not be the most recent backup, as can occur in point-in-time recovery.
For example, if datafile copies are created each Monday evening and are always tagged mondaypmcopy, then the tag refers to the most recent copy (assuming that no SET UNTIL command is issued before restore or recovery). Thus, if complete recovery is desired, this command switches datafile 3 to the most recent Monday evening copy:
SWITCH DATAFILE 3 TO DATAFILECOPY TAG mondaypmcopy;
Tags can indicate the intended purpose or usage of different classes of backups or file copies. For example, datafile copies that are suitable for use in a SWITCH can be tagged differently from file copies that should be used only for RESTORE.
Note:
If you specify a tag when specifying input files to a RESTORE or SWITCH command, then RMAN considers only backup sets with a matching tag when choosing which backup to use