Github user sudheeshkatkam commented on a diff in the pull request:
https://github.com/apache/drill/pull/193#discussion_r45138996
--- Diff:
exec/java-exec/src/main/java/org/apache/drill/exec/planner/logical/DrillDirectScanRel.java
---
@@ -0,0 +1,111 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements. See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership. The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.drill.exec.planner.logical;
+
+import com.google.common.collect.Iterators;
+import org.apache.calcite.plan.RelOptCluster;
+import org.apache.calcite.plan.RelTraitSet;
+import org.apache.calcite.rel.AbstractRelNode;
+import org.apache.calcite.rel.RelWriter;
+import org.apache.calcite.rel.type.RelDataType;
+import org.apache.drill.common.logical.data.LogicalOperator;
+import org.apache.drill.exec.physical.base.PhysicalOperator;
+import org.apache.drill.exec.planner.physical.DrillScanPrel;
+import org.apache.drill.exec.planner.physical.PhysicalPlanCreator;
+import org.apache.drill.exec.planner.physical.PlannerSettings;
+import org.apache.drill.exec.planner.physical.Prel;
+import org.apache.drill.exec.planner.physical.PrelUtil;
+import org.apache.drill.exec.planner.physical.visitor.PrelVisitor;
+import org.apache.drill.exec.record.BatchSchema;
+import org.apache.drill.exec.store.direct.DirectGroupScan;
+
+import java.io.IOException;
+import java.util.Iterator;
+
+/**
+ * Logical and physical RelNode representing a {@link DirectGroupScan}.
This is not backed by a {@link DrillTable},
+ * unlike {@link DrillScanRel}.
+ */
+public class DrillDirectScanRel extends AbstractRelNode implements
DrillScanPrel, DrillRel {
--- End diff --
@jinfengni I'll post the patch with Values approach.
@julianhyde That makes sense.
@jacques-n Since we use data to encode types in Values, pushing Limit
(specially zero) into into Values requires a sizable change (?). Also, I think
[there is a
bug](https://github.com/apache/drill/blob/master/exec/java-exec/src/main/java/org/apache/drill/exec/planner/logical/DrillValuesRel.java#L141)
since Calcite allows for creating a LogicalValues [with types and without
literals](https://github.com/apache/calcite/blob/master/core/src/main/java/org/apache/calcite/rel/logical/LogicalValues.java#L101),
and Drill does not handle this case.
Regarding the above approach (putting a limit 0 on top of scan), I think
fast schema wasn't sufficient because there was only one record batch during
execution (extreme case). Right now, I do not see any specific issue there.
Regarding the note, can you expand on what you mean? Change the visitor
pattern to a logical rule? Or is there a logical rule that conflicts with this
change, and this shorter path should be avoided?
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