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Troubleshooting Oracle Performance by Christian Antognini

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CHAPTER 2Key Concepts

The aim of this chapter is twofold. First, to avoid unnecessary confusion, I'll introduce some terms that are used repeatedly throughout this book. The most important include selectivity and cardinality, soft and hard parses, and bind variable peeking and extended cursor sharing. Second, I'll describe the life cycle of SQL statements. In other words, I'll describe the operations carried out in order to execute SQL statements. During this discussion, special attention will be given to parsing.

Selectivity and Cardinality

The selectivity is a value between 0 and 1 representing the fraction of rows filtered by an operation. For example, if an access operation reads 120 rows from a table and after applying a filter returns ...

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