Rajesh Balamohan created HIVE-24234:
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Summary: Improve checkHashModeEfficiency in VectorGroupByOperator
Key: HIVE-24234
URL: https://issues.apache.org/jira/browse/HIVE-24234
Project: Hive
Issue Type: Improvement
Reporter: Rajesh Balamohan
Currently, {{VectorGroupByOperator::checkHashModeEfficiency}} compares the
number of entries with the number input records that have been processed. For
grouping sets, it accounts for grouping set length as well.
Issue is that, the condition becomes invalid after processing large number of
input records. This prevents the system from switching over to streaming mode.
e.g Assume 500,000 input records processed, with 9 grouping sets, with 100,000
entries in hashtable. Hashtable would never cross 4,500,0000 entries as the max
size itself is 1M by default.
It would be good to compare the input records (adjusted for grouping sets) with
number of output records (along with size of hashtable size) to determine
hashing or streaming mode.
E.g Q67.
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