innobackupex alway backup ibdata1 when I specify with --databases='mydb'

Question

My database files seem to live in $DATADIR/mydb, and ibdata1 live in $DATADIR/, I just want to backup mydb , but everytime innobackupex shows it is copying ibdata1, can any one help me ???

    141120 15:53:42  innobackupex: Starting ibbackup with command: xtrabackup  --defaults-group="mysqld" --backup --suspend-at-end --target-dir=/var/lib/mysqltmp --tmpdir=/var/lib/mysqltmp --extra-lsndir='/var/lib/mysqltmp' --stream=tar
innobackupex: Waiting for ibbackup (pid=22068) to suspend
innobackupex: Suspend file '/var/lib/mysqltmp/xtrabackup_suspended_2'

xtrabackup version 2.2.3 based on MySQL server 5.6.17 Linux (x86_64) (revision id: )
xtrabackup: uses posix_fadvise().
xtrabackup: cd to /data/mysql
xtrabackup: open files limit requested 0, set to 4096
xtrabackup: using the following InnoDB configuration:
xtrabackup:   innodb_data_home_dir = ./
xtrabackup:   innodb_data_file_path = ibdata1:10M:autoextend
xtrabackup:   innodb_log_group_home_dir = ./
xtrabackup:   innodb_log_files_in_group = 2
xtrabackup:   innodb_log_file_size = 268435456
>> log scanned up to (2908642830241)
[01] Streaming ./ibdata1
>> log scanned up to (2908643251964)
>> log scanned up to (2908643769190)
>> log scanned up to (2908644204556)
>> log scanned up to (2908644655653)

Answer 1

If you have innodb_file_per_table enabled, the tables are stored in their own tablespace but the shared tablespace (in your case ibdata1 file) is still used to store other InnoDB's internal data:

• data dictionary (metadata of InnoDB tables)
• change buffer
• doublewrite buffer
• undo logs

So even when you create a backup of a single database, file ibdata1 backed up too.