1. What the VLF?
Mike Hillwig
Boston, MA

2. Mike Hillwig
 SQL Server DBA
 Working with SQL Server since SQL 7
 Senior DBA at hosting division of a financial software
company owned by a large financial institution
 Resume includes Acme Packet, Shawmut Design and
Construction, Equitable Resources

3. Mike Hillwig
 Owned by Two Pugs
 Avid Cook
 Lover of Blue Cheese
 And Bacon
 Geek at Heart

4. Obligatory Social Networking Slide
 mikehillwig.com
 sqlserverpedia.com
 twitter.com/mikehillwig
 anysocialnetworkingsite/mikehillwig

5. Housekeeping
 Blog post at mikehillwig.com/go/vlf
 Please complete your session evaluations.

6. Beware of the Blogs
 There is some amazing
advice out there. But…
 Anybody can put bad
advice on the internet
 Trust people you know
 Assume I’m an idiot
 I don’t trust people who
say “ALWAYS” or
“NEVER”
 Test everything in your
own test environment
first.

7. What is a VLF?
 Very Large Filesystem
 A Virtual Log File
 Construct within a transaction log file
 Breaks your transaction log files into smaller
chunks

8. I am not THE Expert
 Kimberly Tripp from SQLSkills wrote THE
definitive blog post on VLFs.
 Linked from my post at mikehillwig.com/go/vlf

9. Why do we care?
 Too many VLFs can cause performance
problems with DML
 Too few VLFs can cause a performance
problems with transaction log backups

10. How did this happen?
 Most frequent cause is transaction log files
that grow in small increments.
 Are you growing your transaction log files by
10%?
 If so, you probably have a high number of
VLFs.

11. How will I know?
 Cue the Whitney
Houston reference
 DBCC LOGINFO
WITH
TABLERESULTS

12.  Demo

13. The Goldilocks Problem
 This one has too
many
 This one has too few
 This one is just right.
 And there is a just
right for your
environment.

14. But how do we know what’s just right?
 You have to baseline and test
 Know that thousands of VLFs may be too
many
 Know that a handful may be too few
 Number of VLFs will vary based on the size
of your transaction log file

15. Does Size Matter?
 Yes.
 But size isn’t everything.
 Look at throughput
 And look at the size of your VLFs, not just the
number
 And the frequency of your transaction log
backups is a factor as well.

16. This is a Balancing Act
 Amount of throughput
 Size of the VLFs
 Frequency of
transaction log
backups

17. How do we fix it?
 Note how big our transaction log file is today
 Shrink it down
 Manually grow it.
 Be careful not to grow it to more than 8 GB at
a time, though. This could lead to HUGE
VLFs.