15.00 - Read Ahead Count - 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

Read Ahead Count

Purpose  

Specifies the number of data blocks that will be preloaded into memory in advance of the current data block when performing sequential table scans if the ReadAhead field is set to TRUE.

Field Group

Performance

Valid Range

1 through 100 data blocks

Default

1 data block

Changes Take Effect

After the DBS Control Record has been written.

Usage Notes  

Increasing the Read Ahead Count setting can reduce the amount of CPU time spent waiting for read operations to finish. Read Ahead Count should be set high enough to make the typical sequential scan limited only by the CPU, rather than by the read I/O.

The CPU must work harder when data blocks are large or row selection criteria are complex. Consequently, if either of these conditions exist, read ahead counts can be lower.

For example, if a large default data block size is used, most of the tables will consist of large data blocks, and the default ReadAheadCount will suffice. If the default data block size is made very small, most of the tables will consist of small data blocks and system performance might benefit by increasing the ReadAheadCount to 25 or higher.

Related Topics

  • “ReadAhead” on page 416
  • “StandAloneReadAheadCount” on page 442
  • “UseVirtualSysDefault” on page 478