Example of Finding and Fixing Skewed Tables | Teradata Vantage - Example of Finding Skewed Tables by Querying the TableSizeV View - Analytics Database - Teradata Vantage

Database Administration

Deployment
VantageCloud
VantageCore
Edition
Enterprise
IntelliFlex
VMware
Product
Analytics Database
Teradata Vantage
Release Number
17.20
Published
June 2022
Language
English (United States)
Last Update
2023-11-03
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lifecycle
latest
Product Category
Teradata Vantageā„¢

In this example, the SELECT request looks for poorly distributed tables by displaying the average, minimum, and maximum of the CurrentPerm figures allocated on each AMP to every table in the USER database. Each table is reported separately, ordered by name.

SELECT
  TableName (FORMAT 'X(20)'),
  MIN(CurrentPerm) AS "AMP Minimum",
  AVG(CurrentPerm) AS "AMP Average",
  MAX(CurrentPerm) AS "AMP Maximum"
FROM DBC.TableSizeV
WHERE DatabaseName = 'USER'
GROUP BY TableName
ORDER BY TableName; 

Result:

TableName              AMP Minimum   AMP Average   AMP Maximum
--------------------   -----------   -----------   -----------
employee_nupi_ondept   4,096         15,488        30,208
employee_upi_onempid   18,944        19,200        19,968

The result displays two tables. Notice the results show that:

  • The table Employee_upi_onempid is evenly distributed. CurrentPerm is similar across all vprocs (the minimum and maximum are close to the average). Permanent space is relatively evenly distributed across all AMPs in the system.
  • The table Employee_nupi_ondept is poorly distributed. The CurrentPerm figures range from a minimum of 4,096 bytes to a maximum of 30,208 bytes on different AMPs, indicating a wide variance from the average.