[Backport 2.x] Push down limit through eval

core/src/main/java/org/opensearch/sql/planner/optimizer/LogicalPlanOptimizer.java

@@ -12,6 +12,7 @@
 import java.util.List;
 import java.util.stream.Collectors;
 import org.opensearch.sql.planner.logical.LogicalPlan;
+import org.opensearch.sql.planner.optimizer.rule.EvalPushDown;
 import org.opensearch.sql.planner.optimizer.rule.MergeFilterAndFilter;
 import org.opensearch.sql.planner.optimizer.rule.PushFilterUnderSort;
 import org.opensearch.sql.planner.optimizer.rule.read.CreateTableScanBuilder;
@@ -46,6 +47,7 @@ public static LogicalPlanOptimizer create() {
              */
             new MergeFilterAndFilter(),
             new PushFilterUnderSort(),
+            EvalPushDown.PUSH_DOWN_LIMIT,
             /*
              * Phase 2: Transformations that rely on data source push down capability
              */

core/src/main/java/org/opensearch/sql/planner/optimizer/pattern/Patterns.java

@@ -12,6 +12,7 @@
 import java.util.Optional;
 import lombok.experimental.UtilityClass;
 import org.opensearch.sql.planner.logical.LogicalAggregation;
+import org.opensearch.sql.planner.logical.LogicalEval;
 import org.opensearch.sql.planner.logical.LogicalFilter;
 import org.opensearch.sql.planner.logical.LogicalHighlight;
 import org.opensearch.sql.planner.logical.LogicalLimit;
@@ -63,6 +64,10 @@ public static <T extends LogicalPlan> Pattern<LogicalProject> project(Pattern<T>
     return Pattern.typeOf(LogicalProject.class).with(source(pattern));
   }
 
+  public static Pattern<LogicalEval> evalCapture() {
+    return Pattern.typeOf(LogicalEval.class).capturedAs(Capture.newCapture());
+  }
+
   /** Pattern for {@link TableScanBuilder} and capture it meanwhile. */
   public static Pattern<TableScanBuilder> scanBuilder() {
     return Pattern.typeOf(TableScanBuilder.class).capturedAs(Capture.newCapture());

core/src/main/java/org/opensearch/sql/planner/optimizer/rule/EvalPushDown.java

@@ -0,0 +1,82 @@
+/*
+ * Copyright OpenSearch Contributors
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+package org.opensearch.sql.planner.optimizer.rule;
+
+import static org.opensearch.sql.planner.optimizer.pattern.Patterns.evalCapture;
+import static org.opensearch.sql.planner.optimizer.pattern.Patterns.limit;
+import static org.opensearch.sql.planner.optimizer.rule.EvalPushDown.EvalPushDownBuilder.match;
+
+import com.facebook.presto.matching.Capture;
+import com.facebook.presto.matching.Captures;
+import com.facebook.presto.matching.Pattern;
+import com.facebook.presto.matching.pattern.CapturePattern;
+import com.facebook.presto.matching.pattern.WithPattern;
+import java.util.List;
+import java.util.function.BiFunction;
+import lombok.Getter;
+import lombok.experimental.Accessors;
+import org.opensearch.sql.planner.logical.LogicalEval;
+import org.opensearch.sql.planner.logical.LogicalLimit;
+import org.opensearch.sql.planner.logical.LogicalPlan;
+import org.opensearch.sql.planner.optimizer.Rule;
+
+/**
+ * Rule template for all rules related to push down logical plans under eval, so these plans can
+ * avoid blocking by eval and may have chances to be pushed down into table scan by rules in {@link
+ * org.opensearch.sql.planner.optimizer.rule.read.TableScanPushDown}.
+ */
+public class EvalPushDown<T extends LogicalPlan> implements Rule<T> {
+
+  // TODO: Add more rules to push down sort and project
+  /** Push down optimize rule for limit operator. Transform `limit -> eval` to `eval -> limit` */
+  public static final Rule<LogicalLimit> PUSH_DOWN_LIMIT =
+      match(limit(evalCapture()))
+          .apply(
+              (limit, logicalEval) -> {
+                List<LogicalPlan> child = logicalEval.getChild();
+                limit.replaceChildPlans(child);
+                logicalEval.replaceChildPlans(List.of(limit));
+                return logicalEval;
+              });
+
+  private final Capture<LogicalEval> capture;
+
+  @Accessors(fluent = true)
+  @Getter
+  private final Pattern<T> pattern;
+
+  private final BiFunction<T, LogicalEval, LogicalPlan> pushDownFunction;
+
+  @SuppressWarnings("unchecked")
+  public EvalPushDown(
+      WithPattern<T> pattern, BiFunction<T, LogicalEval, LogicalPlan> pushDownFunction) {
+    this.pattern = pattern;
+    this.capture = ((CapturePattern<LogicalEval>) pattern.getPattern()).capture();
+    this.pushDownFunction = pushDownFunction;
+  }
+
+  @Override
+  public LogicalPlan apply(T plan, Captures captures) {
+    LogicalEval logicalEval = captures.get(capture);
+    return pushDownFunction.apply(plan, logicalEval);
+  }
+
+  static class EvalPushDownBuilder<T extends LogicalPlan> {
+
+    private WithPattern<T> pattern;
+
+    public static <T extends LogicalPlan> EvalPushDown.EvalPushDownBuilder<T> match(
+        Pattern<T> pattern) {
+      EvalPushDown.EvalPushDownBuilder<T> builder = new EvalPushDown.EvalPushDownBuilder<>();
+      builder.pattern = (WithPattern<T>) pattern;
+      return builder;
+    }
+
+    public EvalPushDown<T> apply(BiFunction<T, LogicalEval, LogicalPlan> pushDownFunction) {
+      return new EvalPushDown<>(pattern, pushDownFunction);
+    }
+  }
+}

core/src/test/java/org/opensearch/sql/planner/optimizer/LogicalPlanOptimizerTest.java

@@ -15,6 +15,7 @@
 import static org.opensearch.sql.data.model.ExprValueUtils.longValue;
 import static org.opensearch.sql.data.type.ExprCoreType.*;
 import static org.opensearch.sql.planner.logical.LogicalPlanDSL.aggregation;
+import static org.opensearch.sql.planner.logical.LogicalPlanDSL.eval;
 import static org.opensearch.sql.planner.logical.LogicalPlanDSL.filter;
 import static org.opensearch.sql.planner.logical.LogicalPlanDSL.highlight;
 import static org.opensearch.sql.planner.logical.LogicalPlanDSL.limit;
@@ -43,6 +44,7 @@
 import org.opensearch.sql.ast.tree.Sort;
 import org.opensearch.sql.data.type.ExprType;
 import org.opensearch.sql.expression.DSL;
+import org.opensearch.sql.expression.Expression;
 import org.opensearch.sql.expression.NamedExpression;
 import org.opensearch.sql.expression.ReferenceExpression;
 import org.opensearch.sql.planner.logical.LogicalPaginate;
@@ -345,6 +347,27 @@ void table_scan_builder_support_offset_push_down_can_apply_its_rule() {
     assertEquals(project(tableScanBuilder), optimized);
   }
 
+  /** Limit - Eval --> Eval - Limit. */
+  @Test
+  void push_limit_under_eval() {
+    Pair<ReferenceExpression, Expression> evalExpr =
+        Pair.of(DSL.ref("name1", STRING), DSL.ref("name", STRING));
+    assertEquals(
+        eval(limit(tableScanBuilder, 10, 5), evalExpr),
+        optimize(limit(eval(relation("schema", table), evalExpr), 10, 5)));
+  }
+
+  /** Limit - Eval - Scan --> Eval - Scan. */
+  @Test
+  void push_limit_through_eval_into_scan() {
+    when(tableScanBuilder.pushDownLimit(any())).thenReturn(true);
+    Pair<ReferenceExpression, Expression> evalExpr =
+        Pair.of(DSL.ref("name1", STRING), DSL.ref("name", STRING));
+    assertEquals(
+        eval(tableScanBuilder, evalExpr),
+        optimize(limit(eval(relation("schema", table), evalExpr), 10, 5)));
+  }
+
   private LogicalPlan optimize(LogicalPlan plan) {
     final LogicalPlanOptimizer optimizer = LogicalPlanOptimizer.create();
     return optimizer.optimize(plan);

integ-test/src/test/java/org/opensearch/sql/ppl/ExplainIT.java

@@ -76,6 +76,19 @@ public void testSortPushDownExplain() throws Exception {
                 + "| fields age"));
   }
 
+  @Test
+  public void testLimitPushDownExplain() throws Exception {
+    String expected = loadFromFile("expectedOutput/ppl/explain_limit_push.json");
+
+    assertJsonEquals(
+        expected,
+        explainQueryToString(
+            "source=opensearch-sql_test_index_account"
+                + "| eval ageMinus = age - 30 "
+                + "| head 5 "
+                + "| fields ageMinus"));
+  }
+
   String loadFromFile(String filename) throws Exception {
     URI uri = Resources.getResource(filename).toURI();
     return new String(Files.readAllBytes(Paths.get(uri)));

integ-test/src/test/resources/expectedOutput/ppl/explain_limit_push.json

@@ -0,0 +1,27 @@
+{
+  "root": {
+    "name": "ProjectOperator",
+    "description": {
+      "fields": "[ageMinus]"
+    },
+    "children": [
+      {
+        "name": "EvalOperator",
+        "description": {
+          "expressions": {
+            "ageMinus": "-(age, 30)"
+          }
+        },
+        "children": [
+          {
+            "name": "OpenSearchIndexScan",
+            "description": {
+              "request": "OpenSearchQueryRequest(indexName=opensearch-sql_test_index_account, sourceBuilder={\"from\":0,\"size\":5,\"timeout\":\"1m\"}, searchDone=false)"
+            },
+            "children": []
+          }
+        ]
+      }
+    ]
+  }
+}