16.10 - HTMemAlloc - Teradata Database

Teradata Database Utilities

Product
Teradata Database
Release Number
16.10
Published
June 2017
Language
English (United States)
Last Update
2018-04-26
dita:mapPath
zll1480972831047.ditamap
dita:ditavalPath
changebar_rev_16_10_exclude_audience_ie.ditaval

Purpose

Specifies the percentage of cache memory to be allocated to a hash table that is used for a hash join. Hash joins are used as optimizations to a merge joins under specific conditions.

This field should be changed only under the direction of the Teradata Support Center.

Field Group

Performance

Valid Range

0 through 10

A setting of zero prevents hash joins from being used as optimizations.

Default

10

Changes Take Effect

After the DBS Control Record has been written.

Usage Notes

Hash joins can benefit performance when skew is low.

Larger values for HTMemAlloc allow hash join optimizations to be applied to larger tables.

The Optimizer uses the value of HTMemAlloc to determine the size of the hash table as follows:

Hash Table Size = (HTMemAlloc/100) * 20 MB

20 MB is the maximum amount of memory set aside by Teradata Database for hash joins.

Related Topics

For more information on… See…
SkewAllowance field SkewAllowance.
hash table size calculations and possible values SQL Request and Transaction Processing.