Since the beginning, I/O has been one of the main determining factors for overall performance. I/O can easily surpass all other considerations, particularly if an SQL statement asks for a very large result or a missing index causes the scan of a very large table.
”. Overthinking and trying to predict Db2 performance is a slippery slope, and so rather than “thinking” about Db2 performance why not have the database tell you how it will perform. The key to this is the Db2 accounting trace, and subsequent Db2 accounting reports. The accounting reports are useful
Statistics event monitors are an extremely useful way to get periodic monitoring of basic metrics on your system. They're just well-disguised behind a somewhat misleading name.
You can create profiles to selectively control groups of distributed (DBAT) threads and connections, set thresholds for query acceleration (not covered in this article) or provide override properties to model your test subsystem to reflect the computing power of your production environment.
I searched for the manual which would explain how to write proper SQL. I never found it and the more I talked to people on which strategy I should follow, the less useful information I seemed to get. The same was true whenever I asked for general rules to decide which index was needed.