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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