chunfeng pei created CALCITE-4281:
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Summary: fix getMaxRowCount for RelSubset to return reasonable
values
Key: CALCITE-4281
URL: https://issues.apache.org/jira/browse/CALCITE-4281
Project: Calcite
Issue Type: Bug
Components: core
Affects Versions: 1.25.0
Reporter: chunfeng pei
Fix For: next
currently getMaxRowCount(RelSubset rel, RelMetadataQuery mq) only have a short
term fix for CALCITE-1018. https://issues.apache.org/jira/browse/CALCITE-1018
we need a complete solution for this, as suggested in
https://issues.apache.org/jira/browse/CALCITE-1048
quotes: Clearly RelMdMaxRowCount of a RelSubset should be the lowest
max-row-count of any relational expression in that subset. Each kind of
metadata should have a way of deriving a subset's value from the constituent
rel values; in the case of RelMdMaxRowCount the roll-up function is "min".
also a sample solution provided by [~weijie] :
public Double getMaxRowCount(RelSubset rel, RelMetadataQuery mq) { Double
lowest = Double.POSITIVE_INFINITY; for (RelNode node : rel.getRels()) {
Double maxRowCount = mq.getMaxRowCount(node); if (maxRowCount == null) {
continue;
} if (lowest.compareTo(maxRowCount) > 0) \{
lowest = maxRowCount;
}
} return lowest;
}
then comments from [~jhyde] :
quote: I was thinking of doing the same thing in a more abstract way, namely
providing a "[fold|https://en.wikipedia.org/wiki/Fold_(higher-order_function)]"
function.
this ticket is opened to address this issue. this is also related to the
following ticket:
https://issues.apache.org/jira/browse/CALCITE-3963
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