17.00 - 17.05 - Monitoring Disk Utilization - Advanced SQL Engine - Teradata Database

Teradata Vantage™ - Database Administration

Product
Advanced SQL Engine
Teradata Database
Release Number
17.00
17.05
Published
June 2020
Language
English (United States)
Last Update
2021-01-22
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ResUsage and Disk Utilization

The ResNode macro reports disk utilization averages by second.

Parallel Disk Efficiency

Parallel AMP efficiency does not necessarily match parallel disk efficiency. Monitor parallel disk efficiency using ResUsageSvdsk and ResUsageSpdsk tables.

The following table lists common mistakes that can cause skewing and poor parallel efficiency and suggests solutions.

Mistake Solution
A user did not define a PI. The system uses the first column of the table as the default P1. Define a PI with good data distribution.
A user used a null as PI for the target table in a left outer join. Perform any of the following:
  • Choose a different PI.
  • Handle NULL case separately.
  • Use a multiset table.
A user performed a join on column with poor data distribution. For example, the user entered:
SELECT A.colname, B.x, B.y
FROM A, B
WHERE A.colname =
   B.colname;
  • Identify column value and counts. For example, enter:
    SELECT colname, count(*) 
FROM T 
	  HAVING count(*) > 1000
	  GROUP BY 1 ORDER BY 1 Desc;

    The following displays:

    colname   count(*)
codeXYZ    720,000
codeABC      1,200
  • Break the query into two separate SQL statements. For example, handle codeXYZ only in one SQL statement; handle all other cases in another SQL statement.
  • Collect statistics on the join column.