SQL Swiss Army Knife #9 - Fixing VLFs
Download script here: Fix_VLFs.sql
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:
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:
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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