The Hash Table Probe icon indicates that the selection criteria that match the key columns used to create the temporary hash table will be probed to find all of the matching values stored within the hash table. A hash table probe is generally considered when determining the implementation for a secondary table of a join. The use of a hash table probe will allow the optimizer to generate a plan that can take advantage of any non-join selection while creating the temporary hash table. An additional benefit of using a hash table probe is that the data structure of the temporary hash table will usually cause the table data to remain resident within main memory after creation thus reducing paging on the subsequent probe operation. If the icon label is Hash Table Probe Distinct or Hash Table Probe Distinct, Preload, then, for each set of duplicate key entries, only one of the entries will be selected.
Also referred to as: Hash Table Probe, Preload; Hash Table Probe Distinct; Hash Table Probe Distinct, Preload