RE: compressed backup - is this a reasonable size

  • From: "Crisler, Jon" <Jon.Crisler@xxxxxxx>
  • To: <tony_vanlingen@xxxxxxxxxxxxxxxxxxxxx>, <robertgfreeman@xxxxxxxxx>, <oracle-l@xxxxxxxxxxxxx>
  • Date: Fri, 24 Apr 2009 12:15:12 -0400

RMAN compression is very CPU intensive.  The trick to get both
compression and short backup times is to use multiple disk streams and
multiple CPU's.  I typically use 4 to 8 streams, and have used as many
as 48 streams.  Also, some CPU's have poor floating point units which
translates into poor compression performance (very high cpu when
compression is used).  Sun systems based on T1 and T2 cpu's fall into
this category.

Compression has a good effect in that it reduces disk i/o loads for
writes, at the expense of higher cpu usage.  Compression results are
directly affected by the type of data-  I have a system in which 80% of
the database is LOB's and compresses poorly, but I still have to use
compression to save disk space, and cpu usage is sky high.   I have
another db with 500gb that takes 30 min uncompressed but 60 min
compressed- disk usage is only 15% of uncompressed size.

 

________________________________

From: oracle-l-bounce@xxxxxxxxxxxxx
[mailto:oracle-l-bounce@xxxxxxxxxxxxx] On Behalf Of Tony van Lingen
Sent: Wednesday, April 22, 2009 9:16 PM
To: robertgfreeman@xxxxxxxxx; oracle-l@xxxxxxxxxxxxx
Subject: Re: compressed backup - is this a reasonable size

 

That is interesting. I was just discussing this with my collegue who
specialises in RMAN backups. He asserts exactly the opposite where it
comes to backup times. As an example, we have an GIS database of about
1TB (10g) which backs up in 30 mins in standard mode. When he enables
compression it takes up to 6 hours and is very cpu intensive. Apart from
that, he agrees that the compression is quite good.

Apparently the compression also should not be used in combination with a
compressed tape device.

Cheers,
Tony

Robert Freeman wrote: 

Very reasonable. Compression can do wonders for the size of backup sets!
It can also significantly improve overall backup times. What were your
times for the backup compressed and non-compressed and how much of a
difference in CPU did they make.

Be aware that someone on here mentioned a bug with compression just a
few days ago.I looked in Metalink for compression related bugs and found
a few. In a very quick looksee I find most the bugs seem to be related
to backups as opposed to restores. So it seems if you can get a good
backup, then you might well be ok. As always, test test test, your
restores. No piece of software is perfect! :-) On a regular basis
continue to test your restores just in case a bug creeps in. My personal
experience with Compression has been very positive.

Robert

 

Robert G. Freeman
Author:
OCP: Oracle Database 11g Administrator Certified Professional Study
Guide (Sybex)
Oracle Database 11g New Features (Oracle Press)
Portable DBA: Oracle (Oracle Press)
Oracle Database 10g New Features (Oracle Press)
Oracle9i RMAN Backup and Recovery (Oracle Press)
Oracle9i New Features (Oracle Press)
Other various titles out of print now...
Blog: http://robertgfreeman.blogspot.com 
The LDS Church is looking for DBA's. You do have to be a Church member
in
good standing. A lot of kind people write me, concerned I may be
breaking
the law by saying you have to be a Church member. It's legal I promise!
:-) 

 

 

________________________________

From: Jeffrey Beckstrom <JBECKSTROM@xxxxxxxxx>
<mailto:JBECKSTROM@xxxxxxxxx> 
To: oracle-l-freelists <oracle-l@xxxxxxxxxxxxx>
<mailto:oracle-l@xxxxxxxxxxxxx> ; oracle-db-l
<oracle-db-l@xxxxxxxxxxxxxxxxxxxx>
<mailto:oracle-db-l@xxxxxxxxxxxxxxxxxxxx> 
Sent: Wednesday, April 22, 2009 7:36:52 AM
Subject: compressed backup - is this a reasonable size

Just ran the following command.  This is our first RMAN backup.  It
backed up a 17G database into about 3G of files.  Is this
reasonable?????

 

backup as compressed backupset database plus archivelog delete input;

 

Backup states it finished normally.

 

Jeffrey Beckstrom
Database Administrator
Greater Cleveland Regional Transit Authority
1240 W. 6th Street
Cleveland, Ohio 44113

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