vlsi commented on a change in pull request #1703: [CALCITE-2450] Normalize
RexCall predicates when computing digest
URL: https://github.com/apache/calcite/pull/1703#discussion_r362553258
##########
File path:
core/src/main/java/org/apache/calcite/adapter/enumerable/EnumerableHashJoin.java
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@@ -120,24 +121,23 @@ public static EnumerableHashJoin create(
}
}
+ RelOptCostFactory costFactory = planner.getCostFactory();
// Cheaper if the smaller number of rows is coming from the LHS.
// Model this by adding L log L to the cost.
final double rightRowCount = right.estimateRowCount(mq);
final double leftRowCount = left.estimateRowCount(mq);
- if (Double.isInfinite(leftRowCount)) {
- rowCount = leftRowCount;
- } else {
- rowCount += Util.nLogN(leftRowCount);
- }
- if (Double.isInfinite(rightRowCount)) {
- rowCount = rightRowCount;
- } else {
- rowCount += rightRowCount;
+ if (Double.isInfinite(leftRowCount) || Double.isInfinite(rightRowCount)) {
+ return costFactory.makeInfiniteCost();
}
if (isSemiJoin()) {
- return planner.getCostFactory().makeCost(rowCount, 0,
0).multiplyBy(.01d);
+ // For semi- and anti- the right input is hashed
+ rowCount += rightRowCount * 1.1d;
+ return costFactory.makeCost(rowCount, 0, 0).multiplyBy(.01d);
} else {
- return planner.getCostFactory().makeCost(rowCount, 0, 0);
+ // Lots of plans assumed the left join was hashed, so
+ // we adjust a cost accordingly
+ rowCount += leftRowCount * 1.1d;
+ return costFactory.makeCost(rowCount, 0, 0);
Review comment:
The problem here is not 1.1, but the problem is join cardinality estimation.
Calcite tends to over-estimate the join cardinality, thus leftRowCount and
rightRowCount tend to be noise when compared with the estimated join
cardinality, thus all those `+= leftRowCount * 1.1d` change nothing.
So a series of patches (https://issues.apache.org/jira/browse/CALCITE-3666,
https://issues.apache.org/jira/browse/CALCITE-3661) is required before this
costing could provide any meaningful results :(
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