Craig Shallahamer's Blog
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You were brought to this page based on an internet search
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The text below is an except from the book,
Oracle Performance Firefighting, written by
Craig Shallahamer of
OraPub, Inc.
Figures and tables are not included on this page, only their reference.
To order the book in either print or PDF form, click
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©2009, 2010 by Craig Shallahamer. This is copyrighted material.
Please—Out of respect for those involved in the creation of the book and also for
their familes, we ask you to respect the copyright both in intent and deed. Thank you.
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<p>Have you ever heard someone say the IO subsystem needs to be balanced? Of course you have, because an IO subsystem can have very active devices and not very active devices. But as a DBA, it's very unlikely you have heard someone say the CPU subsystem needs to be balanced. That is because any available CPU core can service any transaction in the queue. Unlike an IO subsystem, where reading and writing must occur at an exact spot on a physical spindle, any CPU core can process any waiting transaction. This has massive implications.
p><p>Figure 4-2 shows a four-CPU core subsystem in three different situations. Situation A is very busy CPU subsystem with two processes waiting in the queue. Situation B looks like a very idle CPU subsystem with only one active transaction. However, situation B could also represent a problem. If the transaction being serviced in situation B is a relatively long transaction, why are the other CPUs not participating, but instead standing idle? This is a scalability issue, and as mentioned in Chapter 3's discussion of serialization, everyone-from the businesspeople to the operating system vendors-gets involved, so this situation never occurs.
p><p>Situation C in Figure 4-2 is truly unfortunate. Because there is only one queue, there should never be a situation where processes are waiting in the queue while there are idle CPU cores. Can you imagine standing in a fast food restaurant line, and even though two servers are available, they look at you and tell you to wait? Absurd indeed, and if you ever see this occur (on a computer system), contact your operating system vendor!
p>
©2009, 2010 by Craig Shallahamer. This is copyrighted material.
Please—Out of respect for those involved in the creation of the book and also for
their familes, we ask you to respect the copyright both in intent and deed. Thank you.
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