Add Close Cursor API in v2.

Signed-off-by: Yury-Fridlyand <yury.fridlyand@improving.com>

core/src/main/java/org/opensearch/sql/analysis/Analyzer.java

@@ -43,6 +43,7 @@
 import org.opensearch.sql.ast.expression.UnresolvedExpression;
 import org.opensearch.sql.ast.tree.AD;
 import org.opensearch.sql.ast.tree.Aggregation;
+import org.opensearch.sql.ast.tree.CloseCursor;
 import org.opensearch.sql.ast.tree.Dedupe;
 import org.opensearch.sql.ast.tree.Eval;
 import org.opensearch.sql.ast.tree.FetchCursor;
@@ -83,6 +84,7 @@
 import org.opensearch.sql.expression.parse.ParseExpression;
 import org.opensearch.sql.planner.logical.LogicalAD;
 import org.opensearch.sql.planner.logical.LogicalAggregation;
+import org.opensearch.sql.planner.logical.LogicalCloseCursor;
 import org.opensearch.sql.planner.logical.LogicalDedupe;
 import org.opensearch.sql.planner.logical.LogicalEval;
 import org.opensearch.sql.planner.logical.LogicalFetchCursor;
@@ -572,6 +574,17 @@ public LogicalPlan visitPaginate(Paginate paginate, AnalysisContext context) {
     return new LogicalPaginate(paginate.getPageSize(), List.of(child));
   }
 
+  @Override
+  public LogicalPlan visitFetchCursor(FetchCursor cursor, AnalysisContext context) {
+    return new LogicalFetchCursor(cursor.getCursor(),
+      dataSourceService.getDataSource(DEFAULT_DATASOURCE_NAME).getStorageEngine());
+  }
+
+  @Override
+  public LogicalPlan visitCloseCursor(CloseCursor closeCursor, AnalysisContext context) {
+    return new LogicalCloseCursor(closeCursor.getChild().get(0).accept(this, context));
+  }
+
   /**
    * The first argument is always "asc", others are optional.
    * Given nullFirst argument, use its value. Otherwise just use DEFAULT_ASC/DESC.
@@ -587,10 +600,4 @@ private SortOption analyzeSortOption(List<Argument> fieldArgs) {
     }
     return asc ? SortOption.DEFAULT_ASC : SortOption.DEFAULT_DESC;
   }
-
-  @Override
-  public LogicalPlan visitFetchCursor(FetchCursor cursor, AnalysisContext context) {
-    return new LogicalFetchCursor(cursor.getCursor(),
-      dataSourceService.getDataSource(DEFAULT_DATASOURCE_NAME).getStorageEngine());
-  }
 }

core/src/main/java/org/opensearch/sql/ast/AbstractNodeVisitor.java

@@ -41,6 +41,7 @@
 import org.opensearch.sql.ast.statement.Statement;
 import org.opensearch.sql.ast.tree.AD;
 import org.opensearch.sql.ast.tree.Aggregation;
+import org.opensearch.sql.ast.tree.CloseCursor;
 import org.opensearch.sql.ast.tree.Dedupe;
 import org.opensearch.sql.ast.tree.Eval;
 import org.opensearch.sql.ast.tree.FetchCursor;
@@ -302,6 +303,10 @@ public T visitPaginate(Paginate paginate, C context) {
   }
 
   public T visitFetchCursor(FetchCursor cursor, C context) {
-    return visit(cursor, context);
+    return visitChildren(cursor, context);
+  }
+
+  public T visitCloseCursor(CloseCursor closeCursor, C context) {
+    return visitChildren(closeCursor, context);
   }
 }

core/src/main/java/org/opensearch/sql/ast/tree/CloseCursor.java

@@ -0,0 +1,38 @@
+/*
+ * Copyright OpenSearch Contributors
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+package org.opensearch.sql.ast.tree;
+
+import java.util.List;
+import org.opensearch.sql.ast.AbstractNodeVisitor;
+import org.opensearch.sql.ast.Node;
+
+/**
+ * AST node to represent close cursor operation.
+ * Actually a wrapper to the AST.
+ */
+public class CloseCursor extends UnresolvedPlan {
+
+  /**
+   * An instance of {@link FetchCursor}.
+   */
+  private UnresolvedPlan cursor;
+
+  @Override
+  public <T, C> T accept(AbstractNodeVisitor<T, C> nodeVisitor, C context) {
+    return nodeVisitor.visitCloseCursor(this, context);
+  }
+
+  @Override
+  public UnresolvedPlan attach(UnresolvedPlan child) {
+    this.cursor = child;
+    return this;
+  }
+
+  @Override
+  public List<? extends Node> getChild() {
+    return List.of(cursor);
+  }
+}

core/src/main/java/org/opensearch/sql/executor/execution/CommandPlan.java

@@ -0,0 +1,53 @@
+/*
+ * SPDX-License-Identifier: Apache-2.0
+ *
+ * The OpenSearch Contributors require contributions made to
+ * this file be licensed under the Apache-2.0 license or a
+ * compatible open source license.
+ */
+
+package org.opensearch.sql.executor.execution;
+
+import org.opensearch.sql.ast.tree.UnresolvedPlan;
+import org.opensearch.sql.common.response.ResponseListener;
+import org.opensearch.sql.executor.ExecutionEngine;
+import org.opensearch.sql.executor.QueryId;
+import org.opensearch.sql.executor.QueryService;
+
+/**
+ * Query plan which does not reflect a search query being executed.
+ * It contains a command or an action, for example, a DDL query.
+ */
+public class CommandPlan extends AbstractPlan {
+
+  /**
+   * The query plan ast.
+   */
+  protected final UnresolvedPlan plan;
+
+  /**
+   * Query service.
+   */
+  protected final QueryService queryService;
+
+  protected final ResponseListener<ExecutionEngine.QueryResponse> listener;
+
+  /** Constructor. */
+  public CommandPlan(QueryId queryId, UnresolvedPlan plan, QueryService queryService,
+                     ResponseListener<ExecutionEngine.QueryResponse> listener) {
+    super(queryId);
+    this.plan = plan;
+    this.queryService = queryService;
+    this.listener = listener;
+  }
+
+  @Override
+  public void execute() {
+    queryService.execute(plan, listener);
+  }
+
+  @Override
+  public void explain(ResponseListener<ExecutionEngine.ExplainResponse> listener) {
+    throw new UnsupportedOperationException("CommandPlan does not support explain");
+  }
+}

core/src/main/java/org/opensearch/sql/executor/execution/QueryPlan.java

@@ -18,9 +18,7 @@
 import org.opensearch.sql.executor.QueryService;
 
 /**
- * Query plan. Which includes.
- *
- * <p>select query.
+ * Query plan which includes a <em>select</em> query.
  */
 public class QueryPlan extends AbstractPlan {
 

core/src/main/java/org/opensearch/sql/executor/execution/QueryPlanFactory.java

@@ -17,6 +17,7 @@
 import org.opensearch.sql.ast.statement.Explain;
 import org.opensearch.sql.ast.statement.Query;
 import org.opensearch.sql.ast.statement.Statement;
+import org.opensearch.sql.ast.tree.CloseCursor;
 import org.opensearch.sql.ast.tree.FetchCursor;
 import org.opensearch.sql.ast.tree.UnresolvedPlan;
 import org.opensearch.sql.common.response.ResponseListener;
@@ -88,6 +89,15 @@ boolean canConvertToCursor(UnresolvedPlan plan) {
     return plan.accept(new CanPaginateVisitor(), null);
   }
 
+  /**
+   * Creates a {@link CloseCursor} command on a cursor.
+   */
+  public AbstractPlan createCloseCursor(String cursor,
+      ResponseListener<ExecutionEngine.QueryResponse> queryResponseListener) {
+    return new CommandPlan(QueryId.queryId(), new CloseCursor().attach(new FetchCursor(cursor)),
+        queryService, queryResponseListener);
+  }
+
   @Override
   public AbstractPlan visitQuery(
       Query node,

core/src/main/java/org/opensearch/sql/planner/DefaultImplementor.java

@@ -3,11 +3,11 @@
  * SPDX-License-Identifier: Apache-2.0
  */
 
-
 package org.opensearch.sql.planner;
 
 import org.opensearch.sql.executor.pagination.PlanSerializer;
 import org.opensearch.sql.planner.logical.LogicalAggregation;
+import org.opensearch.sql.planner.logical.LogicalCloseCursor;
 import org.opensearch.sql.planner.logical.LogicalDedupe;
 import org.opensearch.sql.planner.logical.LogicalEval;
 import org.opensearch.sql.planner.logical.LogicalFetchCursor;
@@ -25,6 +25,7 @@
 import org.opensearch.sql.planner.logical.LogicalValues;
 import org.opensearch.sql.planner.logical.LogicalWindow;
 import org.opensearch.sql.planner.physical.AggregationOperator;
+import org.opensearch.sql.planner.physical.CursorCloseOperator;
 import org.opensearch.sql.planner.physical.DedupeOperator;
 import org.opensearch.sql.planner.physical.EvalOperator;
 import org.opensearch.sql.planner.physical.FilterOperator;
@@ -155,6 +156,11 @@ public PhysicalPlan visitFetchCursor(LogicalFetchCursor plan, C context) {
     return new PlanSerializer(plan.getEngine()).convertToPlan(plan.getCursor());
   }
 
+  @Override
+  public PhysicalPlan visitCloseCursor(LogicalCloseCursor node, C context) {
+    return new CursorCloseOperator(visitChild(node, context));
+  }
+
   protected PhysicalPlan visitChild(LogicalPlan node, C context) {
     // Logical operators visited here must have a single child
     return node.getChild().get(0).accept(this, context);

core/src/main/java/org/opensearch/sql/planner/logical/LogicalCloseCursor.java

@@ -0,0 +1,28 @@
+/*
+ * Copyright OpenSearch Contributors
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+package org.opensearch.sql.planner.logical;
+
+import java.util.List;
+import lombok.EqualsAndHashCode;
+import lombok.ToString;
+
+/**
+ * A logical plan node which wraps {@link org.opensearch.sql.planner.LogicalCursor}
+ * and represent a cursor close operation.
+ */
+@ToString
+@EqualsAndHashCode(callSuper = false)
+public class LogicalCloseCursor extends LogicalPlan {
+
+  public LogicalCloseCursor(LogicalPlan child) {
+    super(List.of(child));
+  }
+
+  @Override
+  public <R, C> R accept(LogicalPlanNodeVisitor<R, C> visitor, C context) {
+    return visitor.visitCloseCursor(this, context);
+  }
+}

core/src/main/java/org/opensearch/sql/planner/logical/LogicalFetchCursor.java

@@ -13,6 +13,9 @@
 import org.opensearch.sql.planner.logical.LogicalPlanNodeVisitor;
 import org.opensearch.sql.storage.StorageEngine;
 
+/**
+ * A plan node which represents operation of fetching a next page from the cursor.
+ */
 @EqualsAndHashCode(callSuper = false)
 @ToString
 public class LogicalFetchCursor extends LogicalPlan {

core/src/main/java/org/opensearch/sql/planner/logical/LogicalPlanNodeVisitor.java

@@ -112,4 +112,8 @@ public R visitPaginate(LogicalPaginate plan, C context) {
   public R visitFetchCursor(LogicalFetchCursor plan, C context) {
     return visitNode(plan, context);
   }
+
+  public R visitCloseCursor(LogicalCloseCursor plan, C context) {
+    return visitNode(plan, context);
+  }
 }

core/src/main/java/org/opensearch/sql/planner/physical/CursorCloseOperator.java

@@ -0,0 +1,62 @@
+/*
+ * Copyright OpenSearch Contributors
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+package org.opensearch.sql.planner.physical;
+
+import java.util.List;
+import lombok.RequiredArgsConstructor;
+import org.opensearch.sql.data.model.ExprValue;
+import org.opensearch.sql.executor.ExecutionEngine;
+
+/**
+ * A plan node which blocks issuing a request in {@link #open} and
+ * getting results in {@link #hasNext}, but doesn't block releasing resources in {@link #close}.
+ * Designed to be on top of the deserialized tree.
+ */
+@RequiredArgsConstructor
+public class CursorCloseOperator extends PhysicalPlan {
+
+  // Entire deserialized from cursor plan tree
+  private final PhysicalPlan input;
+
+  @Override
+  public <R, C> R accept(PhysicalPlanNodeVisitor<R, C> visitor, C context) {
+    return visitor.visitCursorClose(this, context);
+  }
+
+  @Override
+  public boolean hasNext() {
+    return false;
+  }
+
+  @Override
+  public ExprValue next() {
+    throw new IllegalStateException();
+  }
+
+  @Override
+  public List<PhysicalPlan> getChild() {
+    return List.of(input);
+  }
+
+  /**
+   * Provides an empty schema, because this plan node is always located on the top of the tree.
+   */
+  @Override
+  public ExecutionEngine.Schema schema() {
+    return new ExecutionEngine.Schema(List.of());
+  }
+
+  // TODO remove
+  @Override
+  public long getTotalHits() {
+    return 0;
+  }
+
+  @Override
+  public void open() {
+    // no-op, no search should be invoked.
+  }
+}

core/src/main/java/org/opensearch/sql/planner/physical/PhysicalPlanNodeVisitor.java

@@ -92,4 +92,8 @@ public R visitAD(PhysicalPlan node, C context) {
   public R visitML(PhysicalPlan node, C context) {
     return visitNode(node, context);
   }
+
+  public R visitCursorClose(CursorCloseOperator node, C context) {
+    return visitNode(node, context);
+  }
 }

core/src/test/java/org/opensearch/sql/analysis/AnalyzerTest.java

@@ -7,6 +7,7 @@
 package org.opensearch.sql.analysis;
 
 import static java.util.Collections.emptyList;
+import static org.junit.jupiter.api.Assertions.assertAll;
 import static org.junit.jupiter.api.Assertions.assertEquals;
 import static org.junit.jupiter.api.Assertions.assertThrows;
 import static org.junit.jupiter.api.Assertions.assertTrue;
@@ -75,6 +76,7 @@
 import org.opensearch.sql.ast.expression.ScoreFunction;
 import org.opensearch.sql.ast.expression.SpanUnit;
 import org.opensearch.sql.ast.tree.AD;
+import org.opensearch.sql.ast.tree.CloseCursor;
 import org.opensearch.sql.ast.tree.FetchCursor;
 import org.opensearch.sql.ast.tree.Kmeans;
 import org.opensearch.sql.ast.tree.ML;
@@ -91,6 +93,7 @@
 import org.opensearch.sql.expression.function.OpenSearchFunctions;
 import org.opensearch.sql.expression.window.WindowDefinition;
 import org.opensearch.sql.planner.logical.LogicalAD;
+import org.opensearch.sql.planner.logical.LogicalCloseCursor;
 import org.opensearch.sql.planner.logical.LogicalFetchCursor;
 import org.opensearch.sql.planner.logical.LogicalFilter;
 import org.opensearch.sql.planner.logical.LogicalMLCommons;
@@ -1651,4 +1654,14 @@ void visit_cursor() {
     assertEquals(new LogicalFetchCursor("test",
         dataSourceService.getDataSource("@opensearch").getStorageEngine()), actual);
   }
+
+  @Test
+  public void visit_close_cursor() {
+    var analyzed = analyze(new CloseCursor().attach(new FetchCursor("pewpew")));
+    assertAll(
+        () -> assertTrue(analyzed instanceof LogicalCloseCursor),
+        () -> assertTrue(analyzed.getChild().get(0) instanceof LogicalFetchCursor),
+        () -> assertEquals("pewpew", ((LogicalFetchCursor) analyzed.getChild().get(0)).getCursor())
+    );
+  }
 }