public Double getPercentageOriginalRows(JoinRelBase rel) {
// Assume any single-table filter conditions have already
// been pushed down.
// REVIEW jvs 28-Mar-2006: As with aggregation, this is
// oversimplified.
// REVIEW jvs 28-Mar-2006: need any special casing for SemiJoinRel?
double left = RelMetadataQuery.getPercentageOriginalRows(rel.getLeft());
double right = RelMetadataQuery.getPercentageOriginalRows(rel.getRight());
return left * right;
}
public Double getPercentageOriginalRows(AggregateRelBase rel) {
// REVIEW jvs 28-Mar-2006: The assumption here seems to be that
// aggregation does not apply any filtering, so it does not modify the
// percentage. That's very much oversimplified.
return RelMetadataQuery.getPercentageOriginalRows(rel.getChild());
}
public Double getPercentageOriginalRows(UnionRelBase rel) {
double numerator = 0.0;
double denominator = 0.0;
// Ignore rel.isDistinct() because it's the same as an aggregate.
// REVIEW jvs 28-Mar-2006: The original Broadbase formula was broken.
// It was multiplying percentage into the numerator term rather than
// than dividing it out of the denominator term, which would be OK if
// there weren't summation going on. Probably the cause of the error
// was the desire to avoid division by zero, which I don't know how to
// handle so I punt, meaning we return a totally wrong answer in the
// case where a huge table has been completely filtered away.
for (RelNode input : rel.getInputs()) {
double rowCount = RelMetadataQuery.getRowCount(input);
double percentage = RelMetadataQuery.getPercentageOriginalRows(input);
if (percentage != 0.0) {
denominator += rowCount / percentage;
numerator += rowCount;
}
}
return quotientForPercentage(numerator, denominator);
}
// Catch-all rule when none of the others apply.
public Double getPercentageOriginalRows(RelNode rel) {
if (rel.getInputs().size() > 1) {
// No generic formula available for multiple inputs.
return null;
}
if (rel.getInputs().size() == 0) {
// Assume no filtering happening at leaf.
return 1.0;
}
RelNode child = rel.getInputs().get(0);
Double childPercentage = RelMetadataQuery.getPercentageOriginalRows(child);
if (childPercentage == null) {
return null;
}
// Compute product of percentage filtering from this rel (assuming any
// filtering is the effect of single-table filters) with the percentage
// filtering performed by the child.
Double relPercentage =
quotientForPercentage(
RelMetadataQuery.getRowCount(rel), RelMetadataQuery.getRowCount(child));
if (relPercentage == null) {
return null;
}
double percent = relPercentage * childPercentage;
// this check is needed in cases where this method is called on a
// physical rel
if ((percent < 0.0) || (percent > 1.0)) {
return null;
}
return relPercentage * childPercentage;
}