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| Performance Monitoring [message #271021 is a reply to message #246965] |
Fri, 28 September 2007 14:11  |
Michel Cadot
Messages: 29419
Registered: March 2007
Location: Nanterre, France, http://... |
Senior Member |
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The following from Joel Garry explains what you have to do to be able to optimize your performances.
- Read Concepts manual.
- Understand that most performance issues come from application issues.
For example, if some silly SQL reads an entire table to get a few rows, you will likely have a lot of unnecessary I/O that won't fill up the SGA.
- Read the Performance manual.
- Understand the optimizer. It can only use the information it is given.
If the statistics it uses are wrong, nonexistent, or skewed in a manner the optimizer doesn't know about, it can choose a silly plan for accessing the data.
Sometimes a full table scan is not silly.
- Understand what plans are and how to use them to understand 4.
- Understand what statspack can tell you.
- Understand when, how and why to use tracing.
- Understand what waits are and how to evaluate them.
- Read and work through books and articles by Jonathan Lewis, Tom Kyte, and Cary Milsap.
- Understand why rules of thumb can be a bad idea for improving the database of customers.
- Understand that tools based strictly on Oracle can be a bit misleading from a systems standpoint, and systems tools can be misleading from Oracle's viewpoint. Simply knowing you have a lot of reads does not mean anything is wrong, after all, what is a database going to be used for? A proper tuning methodology will figure out what critical bottlenecks are, and what to do about them.
- Understand the basics. For example, if you have sequential write-intensive archive writing interfering with random reads and writes for undo and everything else, thrashing a SAN cache, you probably have a configuration problem. If you
have multiple users accessing data, you need to understand how Oracle handles the issues involved.
- Create clear metrics for performance improvement.
- Read Concepts manual.
- Go to #1 above
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