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.
0 through 10
A setting of zero prevents hash joins from being used as optimizations.
Changes Take Effect
After the DBS Control Record has been written.
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.
|For more information on…||See…|
|hash table size calculations and possible values||Teradata Vantage™ - SQL Request and Transaction Processing, B035-1142.|