The original and most common use of Scuba is for real-time
performance monitoring. Julie monitors the performance of facebook.com. She starts by looking at a Scuba dashboard of tens of
graphs showing CPU load on servers; numbers of cache requests,
hits, and misses; network throughput; and many other metrics.
These graphs compare performance week over week, as in Figure 1, or before and after a big code change. Whenever she finds
a significant performance difference, she then drills down through
different columns (often including stack traces), refining the query
until she can pin the difference to a particular block of code and fill
out an urgent bug report.