17.10 - HTMemAlloc - Advanced SQL Engine - Teradata Database

Teradata Vantage™ - Database Utilities

Product
Advanced SQL Engine
Teradata Database
Release Number
17.10
Release Date
July 2021
Content Type
Configuration
Publication ID
B035-1102-171K
Language
English (United States)

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 Vantage for hash joins.

Related Information

For more information on… See…
SkewAllowance field SkewAllowance.
hash table size calculations and possible values Teradata Vantage™ - SQL Request and Transaction Processing, B035-1142.