05-11-2012 09:24 AM
Hash tables are used in the Lookup transformation where lookups are performed against data in memory. This can have a significant impact on performance. Maybe you could be more specific with your question.
05-11-2012 11:09 AM
See the definition from SAS DI documentation.
The optimizer considers a hash join when an index join is eliminated as a possibility. With
a hash join, the smaller table is reconfigured in memory as a hash table. SQL sequentially
scans the larger table and performs row-by-row hash lookup against the small table to form
the result set. A memory-sizing formula, which is not presented here, determines whether
a hash join is chosen.