If indexes are supposed to speed up performance of query, what is meant by a slow index?
A “slow” index is one that does not operate as quickly as expected. There is a myth that this is due to the index itself; that it has somehow degraded, or become faulty. This misconception often drives developers to misguidedly rebuild their database indexes in desperation, often to no effect. One culprit of “slow” indexes is the leaf node chain – when a single value occurs multiple times, the database needs to traverse multiple leaf nodes, which can add up. Another culprit is, of course, accessing the table. Each hit while traversing the index tree requires a table lookup – which is a slow operation – and hundreds of these hits can accumulate even during a single node.
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