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Teradata - What is Row HASH in Teradata ?

asked vishnoiprem August 17, 2014 04:43 AM  

What is Row HASH in Teradata ?


1 Answers

answered By vishnoiprem   0  
The Primary Index is the only thing that determines where a row will reside and the
hashing algorithm never lies. It is important that you understand this process. When a
new row arrives into Teradata, the following steps occur:

Teradata’s PE examines the Primary Index value of the row. Teradata takes that Primary
Index value and runs it through a Hashing Algorithm. The output of the Hashing
Algorithm (i.e., a formula) is a 32-bit Row Hash.
The 32-bit Row Hash will perform two functions:
1. The 32-bit Row Hash will point to a certain spot on the Hash Map, which will
indicate which AMP will hold the row.
2. The 32-bit Row Hash will always remain with the Row as part of a Row ID.
Hashing is a mathematical process where an Index (UPI, NUPI) is converted into a 32-
bit row hash value. The key to this hashing algorithm is the Primary Index. When this
value is determined, the output of this 32-bit value is called the Row Hash.

The Hashing Algorithm will produce random, but consistent row hashes with an end
goal to produce a 32-bit row hash.
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