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Troubleshooting Oracle Performance, Second Edition by Christian Antognini

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SQL Statements with Strong Selectivity

To efficiently process SQL statements with strong selectivity, the data should be accessed through a rowid, an index, or a single-table hash cluster.1 These three possibilities are described in the next sections.

Rowid Access

The most efficient way to access a row is to directly specify its rowid in the WHERE clause. However, to take advantage of that access path, you have to get the rowid first, store it, and then reuse it for further accesses. In other words, it’s a method that can be considered only if a row is accessed at least two times. In practice, this is something that happens quite frequently when SQL statements have strong selectivity. For example, applications used to manually maintain data ...

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