April 27, 2006 at 1:23 am
Hi SQL Gurus,
I have a question about the BackUps:-
How Would a SQL Server know which data has changed from the time You have taken the last Full Database Backup?
Also if their are Transactional Log BackUps Schedule (say after 10 minutes) then whats the use of taking Differential Backups?
April 27, 2006 at 3:43 am
Database changes before, during, and since the last backup are stored in the tables of the database. I think I misunderstand your question.
If you are backing up a transaction log after 10 minutes then there is indeed no need to take a differential database backup because the transaction log backup and the full backup together allow you to restore the database to its current status.
April 27, 2006 at 3:56 am
I try to make it simpler, Mine question is if you take a Full Backup of a database and after that if you take a differential Backup....
How would SQL Server determine which Data has been changed since the last Full Backup.....Whats the Mechanism the SQL Server uses to determine this?
Thnx for Answering 2nd question...........
April 27, 2006 at 9:25 am
Jeetendra,
There's a special page within each data file called a Differential Changed Map (DCM) page that keeps track of which extents in the file have been modified since the last full database backup. A differential backup examines the bits on the DCM pages of each data file in the database and backs up those extents. That's why a differential is generally quicker and smaller than a full.
You might still want to perform differential backups even when performing log backups every ten minutes because it could reduce the recovery time. For example, if you wanted to recover to a point in time 8 hours after the last full backup, you'd have to restore the full and 48 log backups. If there was a differential backup made, say, 4 hours after the full, you would restore the full, the differential, and the last 24 log backups.
Greg
Greg
April 28, 2006 at 5:37 am
Hi Greg,
Thanx a Ton for the explanation...!!!!!!!!
I need one more help from you if you can let me know where i will find the Best Material for SQL Server Architechture which will cover all the minutest details....
If you know any site or have any materials on this It willl be of great help to me.
Once again Thanx a Lot...!!!!!!!!
April 28, 2006 at 9:50 am
I learned this from the book, "Inside SQL Server 2000" by Kalen Delaney. I don't know anybody who digs into the details like she does.
Greg
Greg
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