16.10 - MaxDownRegions - Teradata Database

Teradata Database Utilities

Product
Teradata Database
Release Number
16.10
Published
June 2017
Language
English (United States)
Last Update
2018-04-26
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Purpose

Teradata Database can isolate some file system errors to a specific data or index subtable, or to a contiguous range of rows ("region") in a data or index subtable. In these cases, Teradata Database marks only the affected subtable or region down. This improves system performance and availability by allowing transactions that do not require access to the down subtable or rows to proceed, without causing a database crash that would require a system restart.

However, if several regions in a subtable are marked down, it could indicate a fundamental problem with the subtable itself. Therefore, when a threshold number of down regions is exceeded per AMP, the entire subtable is marked down on all AMPs, making it unavailable to most SQL queries. This threshold can be adjusted by means of the MaxDownRegions field in the General fields group of the DBS Control utility.

The MaxDownRegions field determines the value of this threshold. If the number of down regions per AMP in a subtable exceeds MaxDownRegions, the entire subtable will be marked down and become inaccessible.

Field Group

General

Valid Range

0 through 12

When MaxDownRegions is set to 0, any fatal file system error in a data subtable causes the subtable to be marked down on all AMPs.

Default

6

Changes Take Effect

After the next Teradata Database restart.

Usage Notes

If a data or index subtable is marked down on all AMPs, it is highly recommended that the associated table be rebuilt using the Table Rebuild utility after the source of the problem has been corrected. Alternatively, the table can be dropped and restored from a backup copy. If the problem is with an index subtable, the index can be dropped and recreated.

Tables that are marked down at the time they are rebuilt will remain down after the rebuild. To clear the down status, use the ALTER TABLE ... RESET DOWN statement after the table has been rebuilt.

For more information on the Table Rebuild utility, see Table Rebuild (rebuild).