[GitHub] [calcite] rubenada commented on a change in pull request #2109: [CALCITE-3920] Improve ORDER BY computation in Enumerable convention by exploiting LIMIT

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rubenada commented on a change in pull request #2109:
URL: https://github.com/apache/calcite/pull/2109#discussion_r469934497



##########
File path: core/src/main/java/org/apache/calcite/adapter/enumerable/EnumerableLimitSort.java
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@@ -0,0 +1,146 @@
+/*
+ * 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.calcite.adapter.enumerable;
+
+import org.apache.calcite.linq4j.tree.BlockBuilder;
+import org.apache.calcite.linq4j.tree.Expression;
+import org.apache.calcite.linq4j.tree.Expressions;
+import org.apache.calcite.plan.RelOptCluster;
+import org.apache.calcite.plan.RelOptCost;
+import org.apache.calcite.plan.RelOptPlanner;
+import org.apache.calcite.plan.RelTraitSet;
+import org.apache.calcite.rel.RelCollation;
+import org.apache.calcite.rel.RelNode;
+import org.apache.calcite.rel.core.Sort;
+import org.apache.calcite.rel.metadata.RelMetadataQuery;
+import org.apache.calcite.rex.RexLiteral;
+import org.apache.calcite.rex.RexNode;
+import org.apache.calcite.util.BuiltInMethod;
+import org.apache.calcite.util.Pair;
+
+import static org.apache.calcite.adapter.enumerable.EnumerableLimit.getExpression;
+
+/**
+ * Implementation of {@link org.apache.calcite.rel.core.Sort} in
+ * {@link org.apache.calcite.adapter.enumerable.EnumerableConvention enumerable calling convention}.
+ * It optimizes sorts that have a limit and an optional offset.
+ */
+public class EnumerableLimitSort extends Sort implements EnumerableRel {
+
+  /**
+   * Creates an EnumerableLimitSort.
+   *
+   * <p>Use {@link #create} unless you know what you're doing.
+   */
+  public EnumerableLimitSort(
+      RelOptCluster cluster,
+      RelTraitSet traitSet,
+      RelNode input,
+      RelCollation collation,
+      RexNode offset,
+      RexNode fetch) {
+    super(cluster, traitSet, input, collation, offset, fetch);
+    assert this.getConvention() instanceof EnumerableConvention;
+    assert this.getConvention() == input.getConvention();
+  }
+
+  /** Creates an EnumerableLimitSort. */
+  public static EnumerableLimitSort create(
+      RelNode input,
+      RelCollation collation,
+      RexNode offset,
+      RexNode fetch) {
+    final RelOptCluster cluster = input.getCluster();
+    final RelTraitSet traitSet = cluster.traitSetOf(EnumerableConvention.INSTANCE).replace(
+        collation);
+    return new EnumerableLimitSort(cluster, traitSet, input, collation, offset, fetch);
+  }
+
+  @Override public EnumerableLimitSort copy(
+      RelTraitSet traitSet,
+      RelNode newInput,
+      RelCollation newCollation,
+      RexNode offset,
+      RexNode fetch) {
+    return new EnumerableLimitSort(
+        this.getCluster(),
+        traitSet,
+        newInput,
+        newCollation,
+        offset,
+        fetch);
+  }
+
+  @Override public Result implement(EnumerableRelImplementor implementor, Prefer pref) {
+    final BlockBuilder builder = new BlockBuilder();
+    final EnumerableRel child = (EnumerableRel) this.getInput();
+    final Result result = implementor.visitChild(this, 0, child, pref);
+    final PhysType physType = PhysTypeImpl.of(
+        implementor.getTypeFactory(),
+        this.getRowType(),
+        result.format);
+    Expression childExp = builder.append("child", result.block);

Review comment:
       minor: for consistency reasons inside this method, please declare all variables as "final" (if they are effectively final)




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