15.00 - Effects of Skew on Query Processing Summarized - Teradata Database

Teradata Database Design

prodname
Teradata Database
vrm_release
15.00
category
User Guide
featnum
B035-1094-015K

Effects of Skew on Query Processing Summarized

In the final analysis, a skewed rows per value measure does not necessarily indicate a problem. It is often possible to effect an even distribution of rows across AMPs and evenly distributed workloads when executing a query against skewed data. As long as the Optimizer has good statistics to work with, it is quite good at generating good query plans even when the distribution of table rows is skewed.

It is always better if the data is not skewed, but Teradata Database is better equipped to deal with skew than the database management systems of other vendors, and can often process skewed data successfully while other systems fail the task. Sometimes data is just naturally skewed, and the Optimizer has no choice but to deal with it.