15.00 - ReadAhead - Teradata Database

Teradata Database Utilities

Product
Teradata Database
Release Number
15.00
Content Type
Configuration
Publication ID
B035-1102-015K
Language
English (United States)
Last Update
2018-09-25

ReadAhead

Purpose  

Enables or disables read-ahead operations for sequential table access.

Field Group

Performance

Valid Settings

 

Setting

Description

TRUE

Read-ahead is enabled for sequential file access.

FALSE

No read-ahead is issued.

Default

TRUE

Changes Take Effect

After the DBS Control Record has been written. Operations in progress at the time of the change are not affected.

Usage Notes  

The File System can issue a read-ahead I/O to bring the next data block, or group of data blocks, into memory whenever a data block is read. Preloading data blocks in advance allows processing to occur concurrently with I/Os, and can improve processing time significantly when tables are being scanned sequentially, for example, when running commands such as SCANDISK.

When ReadAhead is enabled, the number of data blocks that are preloaded is determined by the Read Ahead Count, StandAloneReadAheadCount, and UtilityReadAheadCount fields.

Note: If the Cylinder Read feature is enabled, and there are cylinder slots available, all data blocks on the cylinder are read into memory in one read operation. In this case, individual data blocks are not preloaded. For more information on Cylinder Read, see Chapter 7: “Control GDO Editor (ctl).”

Related Topics

  • “Read Ahead Count” on page 418
  • “StandAloneReadAheadCount” on page 442
  • “UseVirtualSysDefault” on page 478