Maryann Xue created PHOENIX-2344:
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Summary: Implement partial stream aggregate
Key: PHOENIX-2344
URL: https://issues.apache.org/jira/browse/PHOENIX-2344
Project: Phoenix
Issue Type: Improvement
Reporter: Maryann Xue
Assignee: Maryann Xue
We now have ordered group-by (stream aggregate) and unordered group-by (hash
aggregate) in Phoenix. Stream aggregate is usually much more beneficial than
hash aggregate in terms of memory usage and pipelining, but it requires that
the aggregate's input is ordered on group-by expressions, i.e. the group-by
expressions is the beginning part of the input's collation (ordering).
However, we could have something in the middle, a stream/hash hybrid aggregate
when the group-by expressions and the input collation share some common part.
For example, we group table T1 by column A, B and T1 is sorted on column A, C,
we'll have the ordered part as A, and the hash part as B. Thus within the range
of a same A, a hash table is used for collecting all different Bs; while at the
changing point of A, we can purge the intermediate hash table and feed the
result for the previous A to next operator.
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