Alex Behm 9f678a7426 IMPALA-5547: Rework FK/PK join detection. ...

Reworks the FK/PK join detection logic to:
- more accurately recognize many-to-many joins
- avoid dim/dim joins for multi-column PKs

The new detection logic maintains our existing philosophy of generally
assuming a FK/PK join, unless there is strong evidence to the
contrary, as follows.

For each set of simple equi-join conjuncts between two tables, we
compute the joint NDV of the right-hand side columns by
multiplication, and if the joint NDV is significantly smaller than
the right-hand side row count, then we are fairly confident that the
right-hand side is not a PK. Otherwise, we assume the set of conjuncts
could represent a FK/PK relationship.

Extends the explain plan to include the outcome of the FK/PK detection
at EXPLAIN_LEVEL > STANDARD.

Performance testing:
1. Full TPC-DS run on 10TB:
   - Q10 improved by >100x
   - Q72 improved by >25x
   - Q17,Q26,Q29 improved by 2x
   - Q64 regressed by 10x
   - Total runtime: Improved by 2x
   - Geomean: Minor improvement
   The regression of Q64 is understood and we will try to address it
   in follow-on changes. The previous plan was better by accident and
   not because of superior logic.
2. Nightly TPC-H and TPC-DS runs:
   - No perf differences

Testing:
- The existing planner test cover the changes.
- Code/hdfs run passed.

Change-Id: I49074fe743a28573cff541ef7dbd0edd88892067
Reviewed-on: http://gerrit.cloudera.org:8080/7257
Reviewed-by: Alex Behm <alex.behm@cloudera.com>
Tested-by: Impala Public Jenkins

2017-07-03 00:04:54 +00:00

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