Yes, the default behavior is that 20% of the data must be modified before statistics are updated automatically (for those desperate to correct me, yes, I know it's more complex a formula than that, but when it comes to very large tables, this is effectively the formula, right?). You can set a traceflag, 2371, to change this behavior. Here are the details. In general, you have to figure out if either of these automated updates are adequate or if you need to manually update statistics. If you do manually update the statistics, you further have to determine if you can use the sampled scans or a full scan to get your statistics. There are no hard and fast rules for me to provide here. You have to figure out your own situation. Just know that there is no one size fits all solution for statistics updates.