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SQL Swiss Army Knife #9 - Fixing VLFs

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Download script here: Fix_VLFs.sql

Hello all,
Here is another post on SQL scripts that may help DBAs, following the series "SQL Swiss Army Knife", this time revisiting the topic of VLFs. I blogged on this subject several times before and if you want to read more about it just click here.

Anyhow, a few months back I knew of a case where a database had over 1.2 million VLFs, and it took a very long time to recover when a restart was performed on the instance. More recently I as made aware of a database with over 930k VLFs. Thankfully, the database owner wanted to preemptively deal with the situation. The database owner was aware of the impact of a high VLF number and wanted a way of quickly finding and dealing with this kind of issue on other servers. This is why I wrote a script that gets an overview of the current VLF status in all databases of a given server, and if the number of VLFs are above a pre-determined threshold, also makes a suggestion of how many and how large the VLFs should be for that particular database.

The output will show:

  • The database name;
  • The transaction log current size and the size it will be after applying suggested changes. Both in MB;
  • The current number of VLFs and the number of VLFs that will remain after applying suggested changes;
  • The amount of growth iterations necessary to get to the suggested size;
  • The transaction log initial size and the autogrow size that should be set;

It will resemble this:

overview

Note that database and file names are purposely blacked out to preserve sensitive data.

In addition, a script is generated with the typical steps needed to deal with the issue, depending on whether the database is in Simple recovery model or not.

Something like this example:

script

Hope you find it useful as much as I did.

Until next time!

EDIT (09-08-2011): missing variable set for sql version. Thanks go to Calvin for finding this bug.

EDIT (26-03-2012): Updated script for SQL 2012 support.

EDIT (19-09-2012): Simplified logic.

EDIT (20-09-2012): Changed grow settings if not SQL Server 2012.

EDIT (11/03/2016): Moved to Github.

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Comments

  • Anonymous
    August 09, 2011
    You declare these variables but never set them.DECLARE @majorver smallint, @minorver smallint, @build smallintThis query can be used to set them.SELECT @majorver=PARSENAME(CONVERT(VARCHAR,SERVERPROPERTY('productversion')),4), @minorver=PARSENAME(CONVERT(VARCHAR,SERVERPROPERTY('productversion')),3), @build=PARSENAME(CONVERT(VARCHAR,SERVERPROPERTY('productversion')),2)
  • Anonymous
    August 09, 2011
    Thanks Calvin for finding this mistake. I meant to set them like this:SELECT@majorver = (@@microsoftversion / 0x1000000) & 0xff,@minorver = (@@microsoftversion / 0x10000) & 0xff,@build = @@microsoftversion & 0xffffI changed the download script accordingly.
  • Anonymous
    September 20, 2012
    The comment has been removed
  • Anonymous
    September 20, 2012
    Hi Kimberly, thanks for the input.You're right, of course, this was introduced in SQL 2005, and happens for growths multiples of 4GB and 8GB. I did some checking and this was fixed only in SQL 2012, and was not back-ported. So, I've rewritten the script accordingly.CheersPL
  • Anonymous
    December 28, 2014
    I have 4 different versions of the script:Fix_VLFs.sql1731.Fix_VLFs.sql5611.Fix_VLFs_3C079A29.sql7585.Fix_VLFs.sqlCan you tell me which is the most current?Thank you!
  • Anonymous
    September 19, 2016
    Really useful! Added to my script vault!BTW, good catch Ms. Tripp!