Transaction Log File and VLF Size

This article by Kimberly Tripp is very interesting. Simply put, she says you want the initial size of your transaction logs set to 8 GB, with auto growth set to 8 GB. This should help keep your Virtual Log File (VLF) sizes below 512 MB, improve performance, and make maintenance during backups much faster.

VLF Image

The article, in part, reads:

First, here’s how the log is divided into VLFs. Each “chunk” that is added, is divided into VLFs at the time the log growth (regardless of whether this is a manual or auto-grow addition) and it’s all dependent on the size that is ADDED not the size of the log itself. So, take a 10MB log that is extended to 50MB, here a 40MB chunk is being added. This 40MB chunk will be divided into 4 VLFs. Here’s the breakdown for chunksize:

chunks less than 64MB and up to 64MB = 4 VLFs
chunks larger than 64MB and up to 1GB = 8 VLFs
chunks larger than 1GB = 16 VLFs

And, what this translates into is that a transaction log of 64GB would have 16 VLFs of 4GB each. As a result, the transaction log could only clear at more than 4GB of log information AND that only when it’s completely inactive. To have a more ideally sized VLF, consider creating the transaction log in 8GB chunks (8GB, then extend it to 16GB, then extend it to 24GB and so forth) so that the number (and size) of your VLFs is more reasonable (in this case 512MB).

You should visit Kimberly’s blog entry for more information. You can also get more information about Virtual Log Files here.


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