Enable push down optimization by default

integ-test/src/test/java/org/opensearch/sql/calcite/standalone/CalcitePPLIntegTestCase.java

@@ -104,7 +104,7 @@ private Settings defaultSettings() {
               .put(Key.FIELD_TYPE_TOLERANCE, true)
               .put(Key.CALCITE_ENGINE_ENABLED, true)
               .put(Key.CALCITE_FALLBACK_ALLOWED, false)
-              .put(Key.CALCITE_PUSHDOWN_ENABLED, false)
+              .put(Key.CALCITE_PUSHDOWN_ENABLED, true)
               .build();
 
       @Override

opensearch/src/main/java/org/opensearch/sql/opensearch/planner/physical/OpenSearchProjectIndexScanRule.java

@@ -67,15 +67,17 @@ public Void visitInputRef(RexInputRef inputRef) {
           }
         };
     visitor.visitEach(project.getProjects());
+    // Only do push down when an actual projection happens
+    if (!selectedColumns.isEmpty() && selectedColumns.size() != scan.getRowType().getFieldCount()) {
+      Mapping mapping = Mappings.target(selectedColumns, scan.getRowType().getFieldCount());
+      CalciteOpenSearchIndexScan newScan = scan.pushDownProject(selectedColumns);
+      final List<RexNode> newProjectRexNodes = RexUtil.apply(mapping, project.getProjects());
 
-    Mapping mapping = Mappings.target(selectedColumns, scan.getRowType().getFieldCount());
-    CalciteOpenSearchIndexScan newScan = scan.pushDownProject(selectedColumns);
-    final List<RexNode> newProjectRexNodes = RexUtil.apply(mapping, project.getProjects());
-
-    if (RexUtil.isIdentity(newProjectRexNodes, newScan.getRowType())) {
-      call.transformTo(newScan);
-    } else {
-      call.transformTo(call.builder().push(newScan).project(newProjectRexNodes).build());
+      if (RexUtil.isIdentity(newProjectRexNodes, newScan.getRowType())) {
+        call.transformTo(newScan);
+      } else {
+        call.transformTo(call.builder().push(newScan).project(newProjectRexNodes).build());
+      }
     }
   }
 

opensearch/src/main/java/org/opensearch/sql/opensearch/setting/OpenSearchSettings.java

@@ -102,7 +102,7 @@ public class OpenSearchSettings extends Settings {
   public static final Setting<?> CALCITE_PUSHDOWN_ENABLED_SETTING =
       Setting.boolSetting(
           Key.CALCITE_PUSHDOWN_ENABLED.getKeyValue(),
-          false,
+          true,
           Setting.Property.NodeScope,
           Setting.Property.Dynamic);
 

opensearch/src/main/java/org/opensearch/sql/opensearch/storage/scan/CalciteOpenSearchIndexScan.java

@@ -24,6 +24,7 @@
 import org.apache.calcite.plan.RelOptTable;
 import org.apache.calcite.plan.RelTraitSet;
 import org.apache.calcite.rel.RelNode;
+import org.apache.calcite.rel.RelWriter;
 import org.apache.calcite.rel.core.Filter;
 import org.apache.calcite.rel.type.RelDataType;
 import org.apache.calcite.rel.type.RelDataTypeFactory;
@@ -96,6 +97,12 @@ public RelNode copy(RelTraitSet traitSet, List<RelNode> inputs) {
     return new CalciteOpenSearchIndexScan(getCluster(), table, osIndex);
   }
 
+  @Override
+  public RelWriter explainTerms(RelWriter pw) {
+    return super.explainTerms(pw)
+        .itemIf("PushDownContext", pushDownContext, !pushDownContext.isEmpty());
+  }
+
   @Override
   public void register(RelOptPlanner planner) {
     super.register(planner);
@@ -147,7 +154,12 @@ public CalciteOpenSearchIndexScan pushDownFilter(Filter filter) {
       CalciteOpenSearchIndexScan newScan = this.copyWithNewSchema(filter.getRowType());
       List<String> schema = this.getRowType().getFieldNames();
       QueryBuilder filterBuilder = PredicateAnalyzer.analyze(filter.getCondition(), schema);
-      newScan.pushDownContext.add(requestBuilder -> requestBuilder.pushDownFilter(filterBuilder));
+      newScan.pushDownContext.add(
+          PushDownAction.of(
+              PushDownType.FILTER,
+              filter.getCondition(),
+              requestBuilder -> requestBuilder.pushDownFilter(filterBuilder)));
+
       // TODO: handle the case where condition contains a score function
       return newScan;
     } catch (Exception e) {
@@ -169,18 +181,47 @@ public CalciteOpenSearchIndexScan pushDownProject(List<Integer> selectedColumns)
     RelDataType newSchema = builder.build();
     CalciteOpenSearchIndexScan newScan = this.copyWithNewSchema(newSchema);
     newScan.pushDownContext.add(
-        requestBuilder -> requestBuilder.pushDownProjectStream(newSchema.getFieldNames().stream()));
+        PushDownAction.of(
+            PushDownType.PROJECT,
+            newSchema.getFieldNames(),
+            requestBuilder ->
+                requestBuilder.pushDownProjectStream(newSchema.getFieldNames().stream())));
     return newScan;
   }
 
+  // TODO: should we consider equivalent among PushDownContexts with different push down sequence?
   static class PushDownContext extends ArrayDeque<PushDownAction> {
     @Override
     public PushDownContext clone() {
       return (PushDownContext) super.clone();
     }
   }
 
-  private interface PushDownAction {
+  private enum PushDownType {
+    FILTER,
+    PROJECT,
+    // AGGREGATION,
+    // SORT,
+    // LIMIT,
+    // HIGHLIGHT,
+    // NESTED
+  }
+
+  private record PushDownAction(PushDownType type, Object digest, AbstractAction action) {
+    static PushDownAction of(PushDownType type, Object digest, AbstractAction action) {
+      return new PushDownAction(type, digest, action);
+    }
+
+    public String toString() {
+      return type + ":" + digest;
+    }
+
+    void apply(OpenSearchRequestBuilder requestBuilder) {
+      action.apply(requestBuilder);
+    }
+  }
+
+  private interface AbstractAction {
     void apply(OpenSearchRequestBuilder requestBuilder);
   }
 }