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Does OLTP table compression reduce size of *uncompressed* RMAN backups?

user1020628
user1020628 Member Posts: 1
edited Jun 9, 2011 12:22PM in Advanced Compression
Let's say I have a table with OLTP compression on, and the uncompressed size is 10GB while the compressed size is 4GB.

If I backup the table using an RMAN script that specifies no RMAN compression, will the rough size of the backup be ~10GB, or ~4GB.

In other words, is the dump of the table's data done by RMAN still compressed, or is it uncompressed?

Thanks,
Tom
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Answers

  • damorgan
    damorgan Member Posts: 14,464 Bronze Crown
    Neither.

    Oracle backs up changed blocks only. The size of the database is irrelevant to the size of the backup.
    With an incremental backup even more so.
  • NS
    NS Member Posts: 337 Bronze Badge
    Backup size is relative to the database size. It will not be more than 4GB.
  • damorgan
    damorgan Member Posts: 14,464 Bronze Crown
    edited Jul 9, 2010 1:16AM
    Please reread the OP's post. Your answer is not correct.

    If you disagree I would be happy to send you instructions for creating a 100GB database that backs up to less than 3GB.
    And also for a 5GB database that backs up to more than 3GB.

    The size of a database is the size of its datafiles. Those datafiles may be empty.
    The size of a table is the size of its allocated extents. Those extents may contain no data.
  • NS
    NS Member Posts: 337 Bronze Badge
    I totally agree with you. All I am saying with regard to OP's question is that, the backup size will not be greater than the compressed database size if RMAN backup is not compressed.
  • 867876
    867876 Member Posts: 1
    Would Oracle allow to turn on RMAN compression on the top of table compression? Any idea if it will provide further compression/ Thanks!
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