Gopal V created HIVE-20983: ------------------------------ Summary: Vectorization: Scale up small hashtables, when collisions are detected Key: HIVE-20983 URL: https://issues.apache.org/jira/browse/HIVE-20983 Project: Hive Issue Type: Bug Reporter: Gopal V
Hive's hashtable estimates are getting better with HyperLogLog stats in place, but an accurate estimate does not always result in a low number of collisions. The hashtables which contain a very small number of items tend to lose their O(1) lookup performance where there are collisions. Since collisions are easy to detect within the fast hashtable implementation, a rehashing to a higher size will help these small hashtables avoid collisions and go back to O(1) perf. -- This message was sent by Atlassian JIRA (v7.6.3#76005)