Explain about Skew Factor.

Skew Factor refers to the row distribution of table among the AMPs. If the data is highly skewed, it means some AMPs are having more rows and some very less. Means data is not evenly distributed. It affects the Teradata's performance. The data distribution or skewness can be controlled by choosing indexes.


There is no particular range for skew factor.  It is suggested to keep skew factor between 5-10.

The factors which impact the skew factor.

- Number of AMPS

- PI of a table

- Number of records in a table

- Size of row in a table


Query to calculate skew factor =>

SELECT databasename,

tablename,

100 * (1 - (AVG(currentperm) / MAX(currentperm))) skew_factor

FROM dbc.tablesize

GROUP BY 1,2

ORDER BY 1,2;