navinvishy opened a new pull request #29170:
URL: https://github.com/apache/spark/pull/29170
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### What changes were proposed in this pull request?
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For a 3-way join of the kind described below, the optimizer fails to infer
the constraint a=1. This appears to be because of the interaction between the
following rules: ColumnPruning, InferFiltersFromConstraints, and
PredicatePushdown.
For the following SQL query:
```
create table t1(a int, b int, c int);
create table t2(a int, b int, c int);
create table t3(a int, b int, c int);
select count(*) from t1 join t2 join t3 on (t1.a = t2.b and t2.b = t3.c and
t3.c = 1);
```
The optimized logical plan produced is:
```
== Optimized Logical Plan ==
Aggregate [count(1) AS count(1)#66L]
+- Project
+- Join Inner, (b#61 = c#65)
:- Project [b#61]
: +- Join Inner, (a#57 = b#61)
: :- Project [a#57]
: : +- Filter isnotnull(a#57)
: : +- HiveTableRelation `default`.`t1`,
org.apache.hadoop.hive.serde2.lazy.LazySimpleSerDe, [a#57, b#58, c#59],
Statistics(sizeInBytes=8.0 EiB)
: +- Project [b#61]
: +- Filter (isnotnull(b#61) AND (b#61 = 1))
: +- HiveTableRelation `default`.`t2`,
org.apache.hadoop.hive.serde2.lazy.LazySimpleSerDe, [a#60, b#61, c#62],
Statistics(sizeInBytes=8.0 EiB)
+- Project [c#65]
+- Filter (isnotnull(c#65) AND (c#65 = 1))
+- HiveTableRelation `default`.`t3`,
org.apache.hadoop.hive.serde2.lazy.LazySimpleSerDe, [a#63, b#64, c#65],
Statistics(sizeInBytes=8.0 EiB)
```
The constraint `a=1` does not get inferred because after column pruning, the
InferFiltersFromConstraints rule on the outer join operator only infers `b=1`,
since the project operator around the join operator drops the constraint that
refers to 'a'. Later, when PushdownPredicates runs again, the `b=1` constraint
gets pushed down to relation 'y'.
In order to resolve this, this patch proposes replacing the
InferFiltersFromConstraints once batch with a batch of
InferFiltersFromConstraints and PredicatePushdown to fixed point. With this
change, the constraint `b=1` will be inferred and pushed down first. The
constraint `a=1` can then be inferred for the inner join operator because `b=1`
is now available in order to infer it. Running PredicatePushdown again will
push `a=1` to its correct position.
### Why are the changes needed?
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Improves performance of optimization. Also this worked correctly earlier in
2.3.
### Does this PR introduce _any_ user-facing change?
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the documentation fix.
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behavior difference if possible.
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If no, write 'No'.
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No
### How was this patch tested?
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Added a unit test. The test should fail if InferFiltersFromConstraints is
run only once.
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