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Message Posted: Mon, 03 Jun 2002 @ 18:21:36 GMT

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John,

Hope you didn't hear that from anyone at Teradata. Teradata's optimizer is cost based. It decides on access paths based on cost estimates of various alternatives. These estimates are based on the data distribution and density statistics that are stored for each query on the table. If statistics aren't available, the optimizer goes through a process called "single AMP sampling" to develop the relative costs. "Single AMP sampling" is better than nothing, but it can easily be misled by highly skewed data and cause the optimizer to generate a very costly (read slow) plan.

Pat Belle
Teradata Certified Master

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