Wednesday, September 15, 2010
How can you view Data Distribution in Teradata ?
Teradata uses HASH values to store data in AMPs. To view data distribution we use Hash Functions.
Hash functions are usually used over primary index columns to find data distribution . We can identify skewness by using this concept .
Following query can be used to find hash values of PI columns
SELECT HASHAMP(HASHBUCKET(HASHROW(<PRIMARY INDEX>))) AS
GROUP BY 1
ORDER BY 2 DESC;
By looking at result , you query you can easily find out the Data Distribution across all AMPs in your system and further you can easily identify un-even data distribution.
HASHROW - returns the row hash value for a given value
HASHBUCKET - the grouping of a specific hash value
HASHAMP - the AMP that is associated with the hash bucket