One popular approach to manual I/O distribution suggests separating a frequently used table from its index. This is not correct. During the course of a transaction, the index is read first, and then the table is read. Because these I/Os occur sequentially, the table and index can be stored on the same disk without contention. It is not sufficient to separate a datafile simply because the datafile contains indexes or table data. The decision to segregate a file should be made only when the I/O rate for that file affects database performance.
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