Ans:
* Hashing is the mechanism through which data is distributed and retrieved to/from AMPs.
* Primary Index (PI) value of a row is the input to the Hashing Algorithm.
* Row Hash (32-bit number) value is the output from this Algorithm.
* Table Id + Row Hash is used to locate Cylinder and Data block.
* Same Primary Index value and data type will always produce same hash value.
* Rows with the same hash value will go to the same AMP.
So data distribution depends directly on the Row Hash uniqueness; be careful while Choosing Indexes in Teradata.
* Hashing is the mechanism through which data is distributed and retrieved to/from AMPs.
* Primary Index (PI) value of a row is the input to the Hashing Algorithm.
* Row Hash (32-bit number) value is the output from this Algorithm.
* Table Id + Row Hash is used to locate Cylinder and Data block.
* Same Primary Index value and data type will always produce same hash value.
* Rows with the same hash value will go to the same AMP.
So data distribution depends directly on the Row Hash uniqueness; be careful while Choosing Indexes in Teradata.
No comments:
Post a Comment