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  SQL Server Tips by Robin Schumacher

The Number One Performance Myth

Whether it’s in the realm of database technology or any other discipline, some maxims are circulated in hushed tones so much that they are taken literally as fact and never questioned, especially when supposed experts mouth the words. Such is the case with the following database performance myth:

“Eighty percent of a database’s overall performance is derived from the code that is written against it.”

This is a complete untruth, or at the very least, an overestimation of the impact that properly written SQL code has against a running physical database. Good coding practices definitely count, often heavily, toward the success of any database application; however, to state affirmatively that they make a contribution of over two-thirds is a stretch.

The reason this cannot pass the reality test is that it is stated independently of what good or bad code can do in the face of poor physical design. The performance problem example presented earlier in this chapter is a shining example of how wrong this adage is.

The physical design constrains all code, good or bad, and has the capability to turn even the best written SQL into virtual molasses. After all, how can an SQL developer obtain unique key index access unless the physical index has been created and is in place? How can a database coder scan only the parts of a table that they need unless that table has been partitioned (SQL Server 2005 and above) to accommodate such a request? Only when a solid physical design is put in place that truly fits the application can SQL code really take off and make for impressive response times. But, good design comes first.

The above book excerpt is from:

High-Performance SQL Server DBA
Tuning & Optimization Secrets

ISBN: 0-9761573-6-5
Robin Schumacher  


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