[jira] [Created] (IMPALA-9875) Deduplicate build in joins with distinct semantics

["Tim Armstrong (Jira)" <ji...@apache.org>]

Tim Armstrong created IMPALA-9875:
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             Summary: Deduplicate build in joins with distinct semantics
                 Key: IMPALA-9875
                 URL: https://issues.apache.org/jira/browse/IMPALA-9875
             Project: IMPALA
          Issue Type: Improvement
          Components: Backend
            Reporter: Tim Armstrong


For left semi and anti joins with only equi-join predicates, we don't need to store duplicates in the hash table, because a probe row will always match the first build row. We could rework the build process in PhjBuilder so that it builds the hash table on the fly and avoids insertion into the BufferedTupleStream if there is a match in the hash table. I.e. the build process would be closer to GroupingAggregator.

Some other joins like that in IMPALA-1706 also have distinct semantics, so maybe this could be applied there too to avoid exploding joins.



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