An average 11g AWR report spans 40 screens broken into approximately 50 sections. That’s a lot, especially for someone who’s not very well familiar with AWR reports, so I decided to make a some sort of a map. The purpose is to show that this report has a certain structure (which may not be obvious at first sight), and knowing this structure can help extract the most essential information in the fastest way possible.
Types of sections
For simplicity, I break AWR report sections into following categories:
1) basic (key information)
2) detalization (provides details on a specific topic briefly covered in the basic section, such as latches, enqueues etc.)
3) advisories (helps find optimal values of parameters)
4) advanced (stuff that is not generally needed, but can be useful on certain occasions — basically, everything not covered in 1-3).
“Load profile” section of the AWR report contains some extremely useful information, and yet it is very often overlooked (often in favor of instance efficiency percentages, which is easier to read but much more likely to mislead). I decided to make some sort of a short guide for it, describing how different statistics in it can be used to better understand performance of a database.
Let’s start with some basic concepts. AWR reports deal with several kinds of time. The simplest kind is the elapsed time , it’s just the interval of time between the start and end snapshots. Another important quantity is DB time, which is defined as time in user calls during that period. It can be (and for a busy system typically is) greater than the elapsed time. However, the reason for that is not the number of CPUs as some experts incorrectly state (apparently, they confuse it with CPU time that we’ll discuss below, e.g. here), it’s that this time is a sum over all active user processes which are using CPU or waiting for something. Note that it only counts time spent in user calls, i.e. background processes are not included in that. Continue reading
Since this is a very popular subject on the OTN forum, I decided to put together a few points about analyzing AWR reports. Continue reading