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Message Posted: Mon, 20 Mar 2006 @ 19:11:11 GMT

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Naveen:

Here is an excerpt from Teradata SQL Reference - Volume 1, Chapter 2: Indexes.

"Rows are distributed across the AMPs using a hashing algorithm that computes a row hash value based on the primary index.

The row hash is a 32-bit value containing a 16-bit destination selection word and a 16-bit remainder.

Teradata relational databases have 65636 hash buckets. The hash buckets are distributed as evenly as possible among the AMPs on a system.

Teradata maintains a hash map -an index of which hash buckets live on which AMPs- that it uses to determine whether rows belong to an AMP based on their row hash values. Row assignment is performed in a manner that ensures as equal a distribution as possible among all the AMPs on a system."

So, in your case the Hash Map references the 160 AMPs of your system. Every row from your tables is sent to its matching AMP based on its Row Hash value and the Row Hash will always remain with the Row as part of the Row Id.

In this way every time a user runs a query looking for information that uses the PI in the Where clause the PE follows the same way to find in which AMP the record is located.

Hope this helps you.

Regards.

Otzmar Vite
Redstar Solutions

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