I ran down the rabbit hole on transaction logs recently. I started with Paul Randal’s post over at the SQL Sentry blog on trimming the transaction log, then went to his video on log analysis. I also glanced at the posts on index cleaning and what index stats don’t tell you. What started out as a quick “what can I do to help transaction logs perform better” became a few hours of reading, executing code and thinking.
However the post that caught my eye was Paul’s post on choosing an index fill factor. I’ve seen various notes on the fact that fill factor can matter for performance and maintenance, but I haven’t often seen someone give some good concrete rules on what you should choose. In a nutshell, here’s Paul’s advice:
- Don’t set a system wide fill factor with sp_configure
- Start with 70 for specific indexes that seem to experience lots of fragmentation
I like this advice. It’s simple, and easy to start using, although the caveat to #2 is that you need to monitor and perhaps adjust the fill factor (up or down from 70) and possibly change your maintenance schedule. I might lean towards leaving my maintenance alone, especially with a script like the SQL Fool Index Defrag Script running and playing with fill factor to ensure I minimized page splits.
There’s also the trade-off of requiring more space for your index (and maintenance) if you move to 70 from 100.
I do think that changing the system wide level is a bad idea. If you aren’t sure what your system wide fill factor is, here’s a post on checking it.