This part of a three-part article consolidating a number of best practices for configuring SQL Server tempdb focuses on configuring multiple files.You won’t just find prescriptive rules here, but also the background to the recommendations and guidance on how to choose the best configuration for any particular environment. In particular this section covers the following:
Use of multiple data files
Another reason you might want to use multiple data files is to increase the I/O throughput to tempdb — especially if it’s running on very fast storage.
When you create multiple data files they will all be in the primary filegroup and SQL Server uses a proportional fill algorithm to determine which file to use for each request to create an object. If all the files are exactly the same size, then SQL Server uses the files in a “round robin” fashion, spreading the load equally across the files. This is, of course, exactly what you want.
Microsoft recommends up to a 1:1 mapping between the number of files and logical CPUs because during testing of massive workloads they’ve seen performance benefits, even with hundreds of data files.
A more pragmatic approach however, is to have a 1:1 mapping between files and logical CPUs up to eight, and then add files if you continue to see allocation contention or if you’re looking to push the I/O subsystem harder. The performance benefit from adding files diminishes each time, and in our experience, eight is the sweet spot, especially if you’re implementing this as a pro-active measure.
Whether or not you configure multiple data files as a best practice on all your SQL Servers or just on those for which you’ve detected issues is a choice only you can make. However, you might want to configure them on all the servers you work with as a proactive measure, as it’s hard to see a downside.