Maryann Xue created CALCITE-1018:
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Summary: SortJoinTransposeRule not firing due to
getMaxRowCount(RelSubset) returning null
Key: CALCITE-1018
URL: https://issues.apache.org/jira/browse/CALCITE-1018
Project: Calcite
Issue Type: Bug
Reporter: Maryann Xue
getMaxRowCount(RelSubset) defaults to getMaxRowCount(RelNode) and returns null,
so if the Join rel has its outer child rel as a RelSubset, the
SortJoinTransposeRule will fail the checkInputForCollationAndLimit check and
will not proceed to push down a limit through join.
Before fix of CALCITE-995 and CALCITE-987, getMaxRowCount(RelSubset) would
return positive infinity, which would cause similar situation but an opposite
effect as firing the rule infinitely when the join's outer child is a RelSubset.
Neither of the above situation was reflected in the test cases for
SortJoinTransposeRule in Calcite, since the RelSubset condition was not covered
by RelOptRule test which uses HepPlanner running with just one or no more than
a couple of rules together.
Basically we need a more accurate way to get max row count for RelSubset,
otherwise checkInputForCollationAndLimit would either always fail or always
succeed for a Limit over a Join over a RelSubset. But I assume, to be real
accurate, we'd have to introduce a similar mechanism to one that computes
bestCost in RelSubset, which I doubt would be worth it.
Another way, which might seem a little ugly, is to add something like
"isSortPushedThrough()" in Sort rel, similar to "isSemiJoinDone()" in Join, in
order to avoid the rule being fired infinitely.
In my Phoenix project, I applied a temporary fix, but it proved to work:
{code}
public class PhoenixRelMdMaxRowCount {
public static final RelMetadataProvider SOURCE =
ReflectiveRelMetadataProvider.reflectiveSource(
BuiltInMethod.MAX_ROW_COUNT.method, new
PhoenixRelMdMaxRowCount());
private PhoenixRelMdMaxRowCount() {
}
public Double getMaxRowCount(RelSubset rel) {
for (RelNode node : rel.getRels()) {
if (node instanceof Sort) {
Sort sort = (Sort) node;
if (sort.fetch != null) {
return (double) RexLiteral.intValue(sort.fetch);
}
}
}
return Double.POSITIVE_INFINITY;
}
}
{code}
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