16.10 - DisableWAL - 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

Determines whether Write-Ahead Logging (WAL) is enabled.

Field Group

File System

Valid Settings

Setting	Description
TRUE	The WAL feature is disabled. Changed data blocks and cylinder indexes are written directly to disk. The DisableWALforDBs field is ignored.
FALSE	The WAL feature is enabled. The items written to the WAL log are determined by the setting of DisableWALforDBs: If DisableWALforDBs is TRUE, changed data blocks are written to disk, and cylinder index changes are written to the WAL log. If DisableWALforDBs is FALSE, changed data blocks are written to the WAL log and cached in memory, or may be written to disk, depending on the specific operation.

Setting

Description

TRUE

The WAL feature is disabled. Changed data blocks and cylinder indexes are written directly to disk. The DisableWALforDBs field is ignored.

FALSE

The WAL feature is enabled. The items written to the WAL log are determined by the setting of DisableWALforDBs:

If DisableWALforDBs is TRUE, changed data blocks are written to disk, and cylinder index changes are written to the WAL log.
If DisableWALforDBs is FALSE, changed data blocks are written to the WAL log and cached in memory, or may be written to disk, depending on the specific operation.

Default

FALSE

Changes Take Effect

After the DBS Control Record has been written.

Usage Notes

WAL is a log-based file system recovery scheme in which modifications to permanent data are written to a log file, the WAL log. The log file contains change records (Redo records) which represent the updates. At key moments, such as transaction commit, the WAL log is forced to disk. In the case of a reset or crash, Redo records can be used to transform the old copy of a permanent data block on disk into the version that existed at the time of the reset.