Differences in Backup Sizes

I have enabled Automatic Backup on a Db2 Database (Windows Server 2003) and also sometimes run a scripted backup using the following commands

db2 backup database FRED to d:\db2_backups with 2 buffers buffer 1024 paralleism 1 compress without prompting

My question related to the sizes of the backups

The Automated Backup is 48Mb
The scripted backup of the same Database is 12Mb
If I remove the compression in the scripted backup the resulting size is 32Mb

Is there really any difference in the contents of the backups and is it just the compression of the scripted backup that makes a difference?

The automated backup will use the autonomic feature of backup to select the optimal buffer size, number of buffers and parallelisms. This difference in buffersize is what accounts for the different image sizes.

Try removing the buffers, buffer and parallelism options off of your backup script and the resulting sizes should be very very close to each other.

Dale McInnis

Thanks Dale,
I took your suggestion and after a bit of experimentation I get the following

backup no options 61.8Mb
backup compress only 11.2Mb
backup 2 buffers parallelism 1 44Mb
backup 1 buffers parallelism 1 49Mb

I wouldn't like to even start to understand why these differences in command make such a difference on the size of the backup but at least I got to something pretty close to the filesize obtained from the automatic backup.

Now if only that file could be automatically compressed. That would help.
The above tests were done on a sample Database. The real DB produces a 1.6Gb file with the Auto Backup process. the corresponding Database backup is only 160Mb with my scripted backup. I guess we will stop the automatic backup.

Thanks again

The reason your automatic backup is larger is that as of v 8.2 we added the DB2BACKUP_INCLUDE_LOGS option on by default. This is not the default for user invoked backups.
So the automatic backup will include the active log set.

Dale