Database Snapshot and Rollback Transactions

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Database Snapshot and Rollback Transactions

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Paul Randal One Orange Chip Points: 29544 More actions · Answer 1

They had to have something else going on, or they're confused by nomenclature - snapshot just can't get bigger than the database - once all pages from the database are copied, there's nothing else that can make the snapshot grow.

Paul Randal
CEO, SQLskills.com: Check out SQLskills online training!
Blog:www.SQLskills.com/blogs/paul Twitter: @PaulRandal
SQL MVP, Microsoft RD, Contributing Editor of TechNet Magazine
Author of DBCC CHECKDB/repair (and other Storage Engine) code of SQL Server 2005

cjeremy74 Ten Centuries Points: 1135 More actions · Answer 2

Thanks for the reply and add'l detail. Glad to know that I was not missing something on the file size.

Jeremy.

Paul White SSC Guru Points: 150467 More actions · Answer 3

Paul Randal (1/11/2010)
...snapshot just can't get bigger than the database - once all pages from the database are copied, there's nothing else that can make the snapshot grow.

True, but it could appear that way:

Consider a database 80GB in size.

A snapshot of that database reaches 78GB in size.

Objects are then deleted from the main database.

The main database is then shrunk to 1GB.

The snapshot is now larger than the database, since extents are never deallocated from the snapshot.

Paul

Paul White
SQLPerformance.com
SQLkiwi blog
@SQL_Kiwi

Paul Randal One Orange Chip Points: 29544 More actions · Answer 4

Yes, that's what I said two replies further up in the thread...

Paul Randal
CEO, SQLskills.com: Check out SQLskills online training!
Blog:www.SQLskills.com/blogs/paul Twitter: @PaulRandal
SQL MVP, Microsoft RD, Contributing Editor of TechNet Magazine
Author of DBCC CHECKDB/repair (and other Storage Engine) code of SQL Server 2005

Paul White SSC Guru Points: 150467 More actions · Answer 5

Paul Randal (1/12/2010)
Yes, that's what I said two replies further up in the thread...

So you did :laugh:

I read that post more than once and missed that part every time! Oh well. The point is well made then I guess.

Paul White
SQLPerformance.com
SQLkiwi blog
@SQL_Kiwi

Paul Randal One Orange Chip Points: 29544 More actions · Answer 6

No worries 🙂

Paul Randal
CEO, SQLskills.com: Check out SQLskills online training!
Blog:www.SQLskills.com/blogs/paul Twitter: @PaulRandal
SQL MVP, Microsoft RD, Contributing Editor of TechNet Magazine
Author of DBCC CHECKDB/repair (and other Storage Engine) code of SQL Server 2005

TomThomson SSC Guru Points: 104773 More actions · Answer 7

The Paul R blog entry is nice and clear - my mind was boggling at the original article, but as soon as I read the phrase "copy-before-write" it all clicked.

Tom