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Re: Large range query stops using indexes
Posted by: KimSeong Loh
Date: June 12, 2007 09:51PM

Full table scan is more likely to be a "sequential read"

Index scan is always a "random read"

Based on the structure of the hard disk, sequential read is much faster than random read. Even if you have the whole index cached in memory, the reading of the rows out of order can still be slow.

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