15.00 - HTMemAlloc - 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

HTMemAlloc

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.

Note: This setting 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” on page 436.

hash table size calculations and possible values

SQL Request and Transaction Processing.