Oracle DBA Interview Questions (2)
Posted on June 4, 2008
11. What is the recommended interval at which to run statspack snapshots， and why?
The most common misuse of STATSPACK is the more is better approach. Often STATSPACK reports spans hours or even days. The times between the snapshots (the colletion points) should, in general, be measured in minutes, not hours and never days.
The STATSPACK reports we like are from 15-minute interval during a busy or peak time, when the performance is at its worst. That provides a very focused look at what was going wrong at that exact moment in time. The problem with a very large STATSPACK snapshot window, where the time between the two snapshorts is measured in hours, is that the events that caused serious performance issues for 20 minutes during peak processing don’t look so bad when they’re spread out over an 8-hour window. It’s also true with STATSPACK that measuring things over too long of a period tends to level them off over time. Nothing will stand out and strike you as being wrong. So, when taking snapshorts, schedule them about 15 to 30 minutes(maximum) apart. You might wait 3 to 4 hours between these two observations, but you should always do them in pairs and within minutes of each other.
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