Re: Incremental Backup and Change Block Tracking Questions

From: Jared Still <>
Date: Fri, 22 Feb 2008 09:43:41 -0800
Message-ID: <>

On Fri, Feb 22, 2008 at 7:52 AM, Sam Bootsma <> wrote:

> 1. Have you found Incremental backups and Change Block Tracking to be
> reliable; i.e, can you reliably backup and then restore and recover?
> Incremental level 1 backups with BCT are much faster than level 1's
without BCT.
Restore is not a problem.
Level 1 backups are a very good thing.

Let's say you took a level 0 yesterday.
Last night a batch job loaded a table in direct path mode, which will not appear in the archive logs.
Today you do a level 1 incremental.
The blocks loaded in direct path mode will be backed up by the level 1, as they are recorded in the BCT.

So in the event of recovery, the level 1 backup not only skips all the archive logs from the end of the level 0 to the beginning of the level 1, the table loaded with direct path will also be recovered, which would not have happened with the level 0 + archive logs.

> 2. What about Oracle compression during an RMAN backup? Is that reliable?

Haven't heard any problems of reliability. You may want to test it however, as
my tests have shown quite a CPU hit.

> 3. How much of a performance hit using the Change Block Tracking feature?
> What about Oracle compression?

< 1% according to Oracle. I haven't measured the actual CPU usage of compression, only
its effect on a running database.

> 4. Do you know if any of these features are additional cost? Do you know
> if there is a view in Oracle that outlines what features come with EE and
> what features are additional cost?
> Can't answer that.

> 5. We also have the option to do compression at the tape drive level. Is
> anybody aware of any reason that Oracle compression (during backup) would be
> better or worse than letting the tape drive do it?

Tape level compression is probably faster. A problem there might differing implementations
of the compression between different versions of tape firmware. Might be a problem if you
need to restore old tapes with new hardware.

6. I have read that restores of a cumulative backup a generally faster than
> restores of a differential backup. What makes cumulative faster? Is it
> simply that RMAN will just one incremental file to restore and recover from
> (plus archive logs)? If there are six differential backups to recover from,
> RMAN should be able to restore and recover the six files without DBA
> intervention. I don't see a significant time difference. Perhaps a couple
> minutes extra because it has six more files to deal with?

Haven't tested it, don't know.

Jared Still
Certifiable Oracle DBA and Part Time Perl Evangelist

Received on Fri Feb 22 2008 - 11:43:41 CST

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