5 июля 2011 г.

oracle: Hash Scans

http://aguppi.blogspot.com/2011/06/oracle-access-path.html

 A hash scan is used to locate rows in a hash cluster, based on a hash value. In a hash cluster, all rows with the same hash value are stored in the same data block. To perform a hash scan, Oracle first obtains the hash value by applying a hash function to a cluster key value specified by the statement. Oracle then scans the data blocks containing rows with that hash value.