System/Kernel Mode CPU Usage – What is Wrong with this Quote?

June 16, 2010

While reading the June 2010 printing of the “Oracle Performance Firefighting” book I found an interesting paragraph that left me wondering if something more, or perhaps something else should be stated.  This quote is from page 104 (this is a long quote, required to not lose the context of the discussion topic - please excuse any typos):

“System time: This is when a core is spending time processing operating system kernel code. Virtual memory management, process scheduling, power management, or essentially any activity not directly related to a user task is classified as system time. From an Oracle-centric perspective, system time is pure overhead. It’s like paying taxes. It must be done, and there are good reasons (usually) for doing it, but it’s not under the control of the business—it’s for the government. Normally, Oracle database CPU subsystems spend about 5% to 40% of their active time in what is called system mode. If you’re from a non-Unix background, you may be more familiar with the term kernel mode or privileged mode, which is, in essence, system time.”

What, if anything, is wrong with the above quote from the book? 

The point of blog articles like this one is not to insult authors who have spent thousands of hours carefully constructing an accurate and helpful book, but instead to suggest that readers investigate when something stated does not exactly match what one believes to be true.  It could be that the author “took a long walk down a short pier”, or that the author is revealing accurate information which simply cannot be found through other resources (and may in the process be directly contradicting information sources you have used in the past).  If you do not investigate in such cases, you may lose an important opportunity to learn something that could prove to be extremely valuable.

Log File Sync – What is Wrong with this Quote?

June 16, 2010

While reading the June 2010 printing of the “Oracle Performance Firefighting” book I found an interesting paragraph that left me wondering if something is missing.  This quote is from page 61 (this is a long quote, required to not lose the context of the discussion topic - please excuse any typos):

“As another example, suppose that you receive a call about long commit times. The users are saying ‘submits’ or ‘saves’ are taking longer today than yesterday. Upon an examination of the average log file sync wait times (which indicate commit times from an Oracle perspective), you discover there is no change from the previous day. Therefore, you know the performance issue is not because of Oracle’s commit mechanism and most likely not related to the database.”  [This period marks the end of Part 3, "IO Wait Time Summary with Event Details"]

What, if anything, is wrong with the above quote from the book? 

The point of blog articles like this one is not to insult authors who have spent thousands of hours carefully constructing an accurate and helpful book, but instead to suggest that readers investigate when something stated does not exactly match what one believes to be true.  It could be that the author “took a long walk down a short pier”, or that the author is revealing accurate information which simply cannot be found through other resources (and may in the process be directly contradicting information sources you have used in the past).  If you do not investigate in such cases, you may lose an important opportunity to learn something that could prove to be extremely valuable.