[jira] [Created] (DRILL-173) Join operator should reuse ValueVectors when duplicate keys are present

["Ben Becker (JIRA)" <ji...@apache.org>]

Ben Becker created DRILL-173:
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             Summary: Join operator should reuse ValueVectors when duplicate keys are present
                 Key: DRILL-173
                 URL: https://issues.apache.org/jira/browse/DRILL-173
             Project: Apache Drill
          Issue Type: Improvement
    Affects Versions: Alpha
            Reporter: Ben Becker


There are cases where joining two record batches can result in redundant work.  Consider a merge join performed on two tables (*t1* and *t2*) with duplicate keys on both sides:

h5. t1
|| key || value ||
| 2 | 'a' |
| 2 | 'b' |

h5. t2
|| key || value ||
| 2 | 'A' |
| 2 | 'B' |
| 2 | 'C' |

The resulting table will contain the cross product of all key values '2':

|| key || t1.value || t2.value ||
| 2 | 'a' | 'A' |
| 2 | 'a' | 'B' |
| 2 | 'a' | 'C' |
| 2 | 'b' | 'A' |
| 2 | 'b' | 'B' |
| 2 | 'b' | 'C' |

The current implementation iteratively copies t2.value from the incoming vectors.  Ideally, the t2.value vector would only be iteratively constructed the first pass; after that it can be copied.

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