vvysotskyi commented on a change in pull request #1386: DRILL-6574: Add option
to push LIMIT(0) on top of SCAN (late limit 0 optimization)
URL: https://github.com/apache/drill/pull/1386#discussion_r203399743
##########
File path:
exec/java-exec/src/main/java/org/apache/drill/exec/planner/sql/handlers/FindLimit0Visitor.java
##########
@@ -126,9 +161,84 @@ public static boolean containsLimit0(final RelNode rel) {
return visitor.isContains();
}
- private boolean contains = false;
+ /**
+ * TODO(DRILL-3993): Use RelBuilder to create a limit node to allow for
applying this optimization in potentially
+ * any of the transformations, but currently this can be applied after Drill
logical transformation, and before
+ * Drill physical transformation.
+ */
+ public static DrillRel addLimitOnTopOfLeafNodes(final DrillRel rel) {
+ final Pointer<Boolean> isUnsupported = new Pointer<>(false);
+
+ // to visit unsupported functions
+ final RexShuttle unsupportedFunctionsVisitor = new RexShuttle() {
+ @Override
+ public RexNode visitCall(RexCall call) {
+ final SqlOperator operator = call.getOperator();
+ if (isUnsupportedScalarFunction(operator)) {
+ isUnsupported.value = true;
+ return call;
+ }
+ return super.visitCall(call);
+ }
+ };
+
+ // to visit unsupported operators
+ final RelShuttle unsupportedOperationsVisitor = new RelShuttleImpl() {
+ @Override
+ public RelNode visit(RelNode other) {
+ if (other instanceof DrillUnionRelBase) {
+ isUnsupported.value = true;
+ return other;
+ } else if (other instanceof DrillProjectRelBase) {
+ other.accept(unsupportedFunctionsVisitor);
Review comment:
Should we also add a check for `isUnsupported` value before calling
`other.accept()` to consider a case when rel node has several inputs and one of
the previous inputs already changed `isUnsupported` value?
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