optimizer

src/mongo/db/query/SConscript

@@ -8,6 +8,7 @@ env.SConscript(
     dirs=[
         "collation",
         "datetime",
+        'optimizer',
     ],
     exports=[
         'env'

src/mongo/db/query/optimizer/SConscript

@@ -0,0 +1,26 @@
+# -*- mode: python -*-
+
+Import("env")
+
+env = env.Clone()
+
+env.Library(
+    target="optimizer",
+    source=[
+        "defs.cpp",
+        "node.cpp",
+    ],
+    LIBDEPS=[
+#        "$BUILD_DIR/mongo/base",
+    ],
+)
+
+env.CppUnitTest(
+    target='optimizer_test',
+    source=[
+        'optimizer_test.cpp',
+    ],
+    LIBDEPS=[
+        'optimizer',
+    ]
+)

src/mongo/db/query/optimizer/defs.cpp

@@ -0,0 +1,40 @@
+/**
+ *    Copyright (C) 2020-present MongoDB, Inc.
+ *
+ *    This program is free software: you can redistribute it and/or modify
+ *    it under the terms of the Server Side Public License, version 1,
+ *    as published by MongoDB, Inc.
+ *
+ *    This program is distributed in the hope that it will be useful,
+ *    but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *    Server Side Public License for more details.
+ *
+ *    You should have received a copy of the Server Side Public License
+ *    along with this program. If not, see
+ *    <http://www.mongodb.com/licensing/server-side-public-license>.
+ *
+ *    As a special exception, the copyright holders give permission to link the
+ *    code of portions of this program with the OpenSSL library under certain
+ *    conditions as described in each individual source file and distribute
+ *    linked combinations including the program with the OpenSSL library. You
+ *    must comply with the Server Side Public License in all respects for
+ *    all of the code used other than as permitted herein. If you modify file(s)
+ *    with this exception, you may extend this exception to your version of the
+ *    file(s), but you are not obligated to do so. If you do not wish to do so,
+ *    delete this exception statement from your version. If you delete this
+ *    exception statement from all source files in the program, then also delete
+ *    it in the license file.
+ */
+
+#include "mongo/db/query/optimizer/defs.h"
+
+namespace mongo::optimizer {
+
+Context::Context() : _nextNodeId(0) {}
+
+NodeIdType Context::getNextNodeId() {
+    return _nextNodeId++;
+}
+
+}  // namespace mongo::optimizer

src/mongo/db/query/optimizer/defs.h

@@ -0,0 +1,52 @@
+/**
+ *    Copyright (C) 2020-present MongoDB, Inc.
+ *
+ *    This program is free software: you can redistribute it and/or modify
+ *    it under the terms of the Server Side Public License, version 1,
+ *    as published by MongoDB, Inc.
+ *
+ *    This program is distributed in the hope that it will be useful,
+ *    but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *    Server Side Public License for more details.
+ *
+ *    You should have received a copy of the Server Side Public License
+ *    along with this program. If not, see
+ *    <http://www.mongodb.com/licensing/server-side-public-license>.
+ *
+ *    As a special exception, the copyright holders give permission to link the
+ *    code of portions of this program with the OpenSSL library under certain
+ *    conditions as described in each individual source file and distribute
+ *    linked combinations including the program with the OpenSSL library. You
+ *    must comply with the Server Side Public License in all respects for
+ *    all of the code used other than as permitted herein. If you modify file(s)
+ *    with this exception, you may extend this exception to your version of the
+ *    file(s), but you are not obligated to do so. If you do not wish to do so,
+ *    delete this exception statement from your version. If you delete this
+ *    exception statement from all source files in the program, then also delete
+ *    it in the license file.
+ */
+
+#pragma once
+
+#include <string>
+
+namespace mongo::optimizer {
+
+using FieldNameType = std::string;
+using CollectionNameType = std::string;
+using ProjectionName = std::string;
+
+using NodeIdType = uint64_t;
+
+class Context {
+public:
+    Context();
+
+    NodeIdType getNextNodeId();
+
+private:
+    NodeIdType _nextNodeId;
+};
+
+}  // namespace mongo::optimizer

src/mongo/db/query/optimizer/filter.h

@@ -0,0 +1,38 @@
+/**
+ *    Copyright (C) 2020-present MongoDB, Inc.
+ *
+ *    This program is free software: you can redistribute it and/or modify
+ *    it under the terms of the Server Side Public License, version 1,
+ *    as published by MongoDB, Inc.
+ *
+ *    This program is distributed in the hope that it will be useful,
+ *    but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *    Server Side Public License for more details.
+ *
+ *    You should have received a copy of the Server Side Public License
+ *    along with this program. If not, see
+ *    <http://www.mongodb.com/licensing/server-side-public-license>.
+ *
+ *    As a special exception, the copyright holders give permission to link the
+ *    code of portions of this program with the OpenSSL library under certain
+ *    conditions as described in each individual source file and distribute
+ *    linked combinations including the program with the OpenSSL library. You
+ *    must comply with the Server Side Public License in all respects for
+ *    all of the code used other than as permitted herein. If you modify file(s)
+ *    with this exception, you may extend this exception to your version of the
+ *    file(s), but you are not obligated to do so. If you do not wish to do so,
+ *    delete this exception statement from your version. If you delete this
+ *    exception statement from all source files in the program, then also delete
+ *    it in the license file.
+ */
+
+#pragma once
+
+#include <string>
+
+namespace mongo::optimizer {
+
+using FilterType = std::string;
+
+}  // namespace mongo::optimizer

src/mongo/db/query/optimizer/node.cpp

@@ -0,0 +1,211 @@
+/**
+ *    Copyright (C) 2020-present MongoDB, Inc.
+ *
+ *    This program is free software: you can redistribute it and/or modify
+ *    it under the terms of the Server Side Public License, version 1,
+ *    as published by MongoDB, Inc.
+ *
+ *    This program is distributed in the hope that it will be useful,
+ *    but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *    Server Side Public License for more details.
+ *
+ *    You should have received a copy of the Server Side Public License
+ *    along with this program. If not, see
+ *    <http://www.mongodb.com/licensing/server-side-public-license>.
+ *
+ *    As a special exception, the copyright holders give permission to link the
+ *    code of portions of this program with the OpenSSL library under certain
+ *    conditions as described in each individual source file and distribute
+ *    linked combinations including the program with the OpenSSL library. You
+ *    must comply with the Server Side Public License in all respects for
+ *    all of the code used other than as permitted herein. If you modify file(s)
+ *    with this exception, you may extend this exception to your version of the
+ *    file(s), but you are not obligated to do so. If you do not wish to do so,
+ *    delete this exception statement from your version. If you delete this
+ *    exception statement from all source files in the program, then also delete
+ *    it in the license file.
+ */
+
+#include "mongo/db/query/optimizer/node.h"
+#include "mongo/db/query/optimizer/visitor.h"
+
+namespace mongo::optimizer {
+
+Node::Node(Context& ctx) : _nodeId(ctx.getNextNodeId()), _children() {}
+
+Node::Node(Context& ctx, NodePtr child) : _nodeId(ctx.getNextNodeId()) {
+    _children.push_back(std::move(child));
+}
+
+Node::Node(Context& ctx, std::vector<NodePtr> children)
+    : _nodeId(ctx.getNextNodeId()), _children(std::move(children)) {}
+
+void Node::generateMemoBase(std::ostringstream& os) {
+    os << "NodeId: " << _nodeId << "\n";
+}
+
+std::string Node::generateMemo() {
+    std::ostringstream os;
+
+    class MemoVisitor: public AbstractVisitor
+    {
+    protected:
+        void visit(ScanNode& node) override {
+            node.generateMemoInternal(os);
+        }
+        void visit(MultiJoinNode& node) override {
+            node.generateMemoInternal(os);
+        }
+        void visit(UnionNode& node) override {
+            node.generateMemoInternal(os);
+        }
+        void visit(GroupByNode& node) override {
+            node.generateMemoInternal(os);
+        }
+        void visit(UnwindNode& node) override {
+            node.generateMemoInternal(os);
+        }
+        void visit(WindNode& node) override {
+            node.generateMemoInternal(os);
+        }
+    public:
+        std::ostringstream os;
+    };
+
+    MemoVisitor visitor;
+    visitPreOrder(visitor);
+    return visitor.os.str();
+}
+
+void Node::visitPreOrder(AbstractVisitor& visitor) {
+    visit(visitor);
+    for (const NodePtr& ptr: _children) {
+        ptr->visitPreOrder(visitor);
+    }
+}
+
+NodePtr ScanNode::create(Context& ctx, CollectionNameType collectionName) {
+    return NodePtr(new ScanNode(ctx, std::move(collectionName)));
+}
+
+ScanNode::ScanNode(Context& ctx, CollectionNameType collectionName)
+    : Node(ctx), _collectionName(std::move(collectionName)) {}
+
+void ScanNode::generateMemoInternal(std::ostringstream& os) {
+    Node::generateMemoBase(os);
+    os << "Scan" << "\n";
+}
+
+void ScanNode::visit(AbstractVisitor& visitor) {
+    visitor.visit(*this);
+}
+
+NodePtr MultiJoinNode::create(Context& ctx,
+                              FilterSet filterSet,
+                              ProjectionMap projectionMap,
+                              std::vector<NodePtr> children) {
+    return NodePtr(new MultiJoinNode(
+        ctx, std::move(filterSet), std::move(projectionMap), std::move(children)));
+}
+
+MultiJoinNode::MultiJoinNode(Context& ctx,
+                             FilterSet filterSet,
+                             ProjectionMap projectionMap,
+                             std::vector<NodePtr> children)
+    : Node(ctx, std::move(children)),
+      _filterSet(std::move(filterSet)),
+      _projectionMap(std::move(projectionMap)) {}
+
+void MultiJoinNode::generateMemoInternal(std::ostringstream& os) {
+    Node::generateMemoBase(os);
+    os << "MultiJoin" << "\n";
+}
+
+void MultiJoinNode::visit(AbstractVisitor& visitor) {
+    visitor.visit(*this);
+}
+
+NodePtr UnionNode::create(Context& ctx, std::vector<NodePtr> children) {
+    return NodePtr(new UnionNode(ctx, std::move(children)));
+}
+
+UnionNode::UnionNode(Context& ctx, std::vector<NodePtr> children)
+    : Node(ctx, std::move(children)) {}
+
+void UnionNode::generateMemoInternal(std::ostringstream& os) {
+    Node::generateMemoBase(os);
+    os << "Union" << "\n";
+}
+
+void UnionNode::visit(AbstractVisitor& visitor) {
+    visitor.visit(*this);
+}
+
+NodePtr GroupByNode::create(Context& ctx,
+                            GroupByNode::GroupByVector groupByVector,
+                            GroupByNode::ProjectionMap projectionMap,
+                            NodePtr child) {
+    return NodePtr(
+        new GroupByNode(ctx, std::move(groupByVector), std::move(projectionMap), std::move(child)));
+}
+
+GroupByNode::GroupByNode(Context& ctx,
+                         GroupByNode::GroupByVector groupByVector,
+                         GroupByNode::ProjectionMap projectionMap,
+                         NodePtr child)
+    : Node(ctx, std::move(child)),
+      _groupByVector(std::move(groupByVector)),
+      _projectionMap(std::move(projectionMap)) {}
+
+void GroupByNode::generateMemoInternal(std::ostringstream& os) {
+    Node::generateMemoBase(os);
+    os << "GroupBy" << "\n";
+}
+
+void GroupByNode::visit(AbstractVisitor& visitor) {
+    visitor.visit(*this);
+}
+
+NodePtr UnwindNode::create(Context& ctx,
+                           ProjectionName projectionName,
+                           const bool retainNonArrays,
+                           NodePtr child) {
+    return NodePtr(
+        new UnwindNode(ctx, std::move(projectionName), retainNonArrays, std::move(child)));
+}
+
+UnwindNode::UnwindNode(Context& ctx,
+                       ProjectionName projectionName,
+                       const bool retainNonArrays,
+                       NodePtr child)
+    : Node(ctx, std::move(child)),
+      _projectionName(std::move(projectionName)),
+      _retainNonArrays(retainNonArrays) {}
+
+void UnwindNode::generateMemoInternal(std::ostringstream& os) {
+    Node::generateMemoBase(os);
+    os << "Unwind" << "\n";
+}
+
+void UnwindNode::visit(AbstractVisitor& visitor) {
+    visitor.visit(*this);
+}
+
+NodePtr WindNode::create(Context& ctx, ProjectionName projectionName, NodePtr child) {
+    return NodePtr(new WindNode(ctx, std::move(projectionName), std::move(child)));
+}
+
+WindNode::WindNode(Context& ctx, ProjectionName projectionName, NodePtr child)
+    : Node(ctx, std::move(child)), _projectionName(std::move(projectionName)) {}
+
+void WindNode::generateMemoInternal(std::ostringstream& os) {
+    Node::generateMemoBase(os);
+    os << "Wind" << "\n";
+}
+
+void WindNode::visit(AbstractVisitor& visitor) {
+    visitor.visit(*this);
+}
+
+}  // namespace mongo::optimizer

src/mongo/db/query/optimizer/node.h

@@ -0,0 +1,191 @@
+/**
+ *    Copyright (C) 2020-present MongoDB, Inc.
+ *
+ *    This program is free software: you can redistribute it and/or modify
+ *    it under the terms of the Server Side Public License, version 1,
+ *    as published by MongoDB, Inc.
+ *
+ *    This program is distributed in the hope that it will be useful,
+ *    but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *    Server Side Public License for more details.
+ *
+ *    You should have received a copy of the Server Side Public License
+ *    along with this program. If not, see
+ *    <http://www.mongodb.com/licensing/server-side-public-license>.
+ *
+ *    As a special exception, the copyright holders give permission to link the
+ *    code of portions of this program with the OpenSSL library under certain
+ *    conditions as described in each individual source file and distribute
+ *    linked combinations including the program with the OpenSSL library. You
+ *    must comply with the Server Side Public License in all respects for
+ *    all of the code used other than as permitted herein. If you modify file(s)
+ *    with this exception, you may extend this exception to your version of the
+ *    file(s), but you are not obligated to do so. If you do not wish to do so,
+ *    delete this exception statement from your version. If you delete this
+ *    exception statement from all source files in the program, then also delete
+ *    it in the license file.
+ */
+
+#pragma once
+
+#include <memory>
+#include <sstream>
+#include <string>
+#include <unordered_map>
+#include <unordered_set>
+#include <utility>
+#include <vector>
+
+#include "mongo/db/query/optimizer/defs.h"
+#include "mongo/db/query/optimizer/filter.h"
+#include "mongo/db/query/optimizer/projection.h"
+#include "mongo/db/query/optimizer/props.h"
+
+
+namespace mongo::optimizer {
+
+class Node;
+using NodePtr = std::unique_ptr<Node>;
+
+class AbstractVisitor;
+
+class Node {
+    friend class AbstractVisitor;
+
+protected:
+    explicit Node(Context& ctx);
+    explicit Node(Context& ctx, NodePtr child);
+    explicit Node(Context& ctx, std::vector<NodePtr> children);
+
+    virtual void generateMemoBase(std::ostringstream& os);
+
+    virtual void visit(AbstractVisitor& visitor) = 0;
+
+    virtual void visitPreOrder(AbstractVisitor& visitor) final;
+
+    // clone
+public:
+    Node() = delete;
+
+    virtual std::string generateMemo() final;
+
+private:
+    const NodeIdType _nodeId;
+    std::vector<NodePtr> _children;
+};
+
+class ScanNode : public Node {
+public:
+    static NodePtr create(Context& ctx, CollectionNameType collectionName);
+
+    void generateMemoInternal(std::ostringstream& os);
+
+protected:
+    void visit(AbstractVisitor& visitor) override;
+
+private:
+    explicit ScanNode(Context& ctx, CollectionNameType collectionName);
+
+    const CollectionNameType _collectionName;
+};
+
+class MultiJoinNode : public Node {
+public:
+    using FilterSet = std::unordered_set<FilterType>;
+    using ProjectionMap = std::unordered_map<ProjectionName, ProjectionType>;
+
+    static NodePtr create(Context& ctx,
+                          FilterSet filterSet,
+                          ProjectionMap projectionMap,
+                          std::vector<NodePtr> children);
+
+    void generateMemoInternal(std::ostringstream& os);
+
+protected:
+    void visit(AbstractVisitor& visitor) override;
+
+private:
+    explicit MultiJoinNode(Context& ctx,
+                           FilterSet filterSet,
+                           ProjectionMap projectionMap,
+                           std::vector<NodePtr> children);
+
+    FilterSet _filterSet;
+    ProjectionMap _projectionMap;
+};
+
+class UnionNode : public Node {
+public:
+    static NodePtr create(Context& ctx, std::vector<NodePtr> children);
+
+    void generateMemoInternal(std::ostringstream& os);
+
+protected:
+    void visit(AbstractVisitor& visitor) override;
+
+private:
+    explicit UnionNode(Context& ctx, std::vector<NodePtr> children);
+};
+
+class GroupByNode : public Node {
+public:
+    using GroupByVector = std::vector<ProjectionName>;
+    using ProjectionMap = std::unordered_map<ProjectionName, ProjectionType>;
+
+    static NodePtr create(Context& ctx,
+                          GroupByVector groupByVector,
+                          ProjectionMap projectionMap,
+                          NodePtr child);
+
+    void generateMemoInternal(std::ostringstream& os);
+
+protected:
+    void visit(AbstractVisitor& visitor) override;
+
+private:
+    explicit GroupByNode(Context& ctx,
+                         GroupByVector groupByVector,
+                         ProjectionMap projectionMap,
+                         NodePtr child);
+
+    GroupByVector _groupByVector;
+    ProjectionMap _projectionMap;
+};
+
+class UnwindNode : public Node {
+public:
+    static NodePtr create(Context& ctx,
+                          ProjectionName projectionName,
+                          bool retainNonArrays,
+                          NodePtr child);
+
+    void generateMemoInternal(std::ostringstream& os);
+
+protected:
+
+    void visit(AbstractVisitor& visitor) override;
+
+private:
+    UnwindNode(Context& ctx, ProjectionName projectionName, bool retainNonArrays, NodePtr child);
+
+    const ProjectionName _projectionName;
+    const bool _retainNonArrays;
+};
+
+class WindNode : public Node {
+public:
+    static NodePtr create(Context& ctx, ProjectionName projectionName, NodePtr child);
+
+    void generateMemoInternal(std::ostringstream& os);
+
+protected:
+    void visit(AbstractVisitor& visitor) override;
+
+private:
+    WindNode(Context& ctx, ProjectionName projectionName, NodePtr child);
+
+    const ProjectionName _projectionName;
+};
+
+}  // namespace mongo::optimizer

src/mongo/db/query/optimizer/optimizer_test.cpp

@@ -0,0 +1,45 @@
+/**
+ *    Copyright (C) 2020-present MongoDB, Inc.
+ *
+ *    This program is free software: you can redistribute it and/or modify
+ *    it under the terms of the Server Side Public License, version 1,
+ *    as published by MongoDB, Inc.
+ *
+ *    This program is distributed in the hope that it will be useful,
+ *    but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *    Server Side Public License for more details.
+ *
+ *    You should have received a copy of the Server Side Public License
+ *    along with this program. If not, see
+ *    <http://www.mongodb.com/licensing/server-side-public-license>.
+ *
+ *    As a special exception, the copyright holders give permission to link the
+ *    code of portions of this program with the OpenSSL library under certain
+ *    conditions as described in each individual source file and distribute
+ *    linked combinations including the program with the OpenSSL library. You
+ *    must comply with the Server Side Public License in all respects for
+ *    all of the code used other than as permitted herein. If you modify file(s)
+ *    with this exception, you may extend this exception to your version of the
+ *    file(s), but you are not obligated to do so. If you do not wish to do so,
+ *    delete this exception statement from your version. If you delete this
+ *    exception statement from all source files in the program, then also delete
+ *    it in the license file.
+ */
+
+#include "mongo/db/query/optimizer/node.h"
+#include "mongo/unittest/unittest.h"
+
+namespace mongo::optimizer {
+namespace {
+
+TEST(Optimizer, Basic) {
+    Context ctx;
+
+    NodePtr ptr = ScanNode::create(ctx, "test");
+    const std::string& s = ptr->generateMemo();
+    NodePtr ptr1 = ScanNode::create(ctx, "test");
+}
+
+}  // namespace
+}  // namespace mongo::optimizer

src/mongo/db/query/optimizer/projection.h

@@ -0,0 +1,38 @@
+/**
+ *    Copyright (C) 2020-present MongoDB, Inc.
+ *
+ *    This program is free software: you can redistribute it and/or modify
+ *    it under the terms of the Server Side Public License, version 1,
+ *    as published by MongoDB, Inc.
+ *
+ *    This program is distributed in the hope that it will be useful,
+ *    but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *    Server Side Public License for more details.
+ *
+ *    You should have received a copy of the Server Side Public License
+ *    along with this program. If not, see
+ *    <http://www.mongodb.com/licensing/server-side-public-license>.
+ *
+ *    As a special exception, the copyright holders give permission to link the
+ *    code of portions of this program with the OpenSSL library under certain
+ *    conditions as described in each individual source file and distribute
+ *    linked combinations including the program with the OpenSSL library. You
+ *    must comply with the Server Side Public License in all respects for
+ *    all of the code used other than as permitted herein. If you modify file(s)
+ *    with this exception, you may extend this exception to your version of the
+ *    file(s), but you are not obligated to do so. If you do not wish to do so,
+ *    delete this exception statement from your version. If you delete this
+ *    exception statement from all source files in the program, then also delete
+ *    it in the license file.
+ */
+
+#pragma once
+
+#include <string>
+
+namespace mongo::optimizer {
+
+using ProjectionType = std::string;
+
+}  // namespace mongo::optimizer

src/mongo/db/query/optimizer/props.h

@@ -0,0 +1,38 @@
+/**
+ *    Copyright (C) 2020-present MongoDB, Inc.
+ *
+ *    This program is free software: you can redistribute it and/or modify
+ *    it under the terms of the Server Side Public License, version 1,
+ *    as published by MongoDB, Inc.
+ *
+ *    This program is distributed in the hope that it will be useful,
+ *    but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *    Server Side Public License for more details.
+ *
+ *    You should have received a copy of the Server Side Public License
+ *    along with this program. If not, see
+ *    <http://www.mongodb.com/licensing/server-side-public-license>.
+ *
+ *    As a special exception, the copyright holders give permission to link the
+ *    code of portions of this program with the OpenSSL library under certain
+ *    conditions as described in each individual source file and distribute
+ *    linked combinations including the program with the OpenSSL library. You
+ *    must comply with the Server Side Public License in all respects for
+ *    all of the code used other than as permitted herein. If you modify file(s)
+ *    with this exception, you may extend this exception to your version of the
+ *    file(s), but you are not obligated to do so. If you do not wish to do so,
+ *    delete this exception statement from your version. If you delete this
+ *    exception statement from all source files in the program, then also delete
+ *    it in the license file.
+ */
+
+#pragma once
+
+#include <string>
+
+namespace mongo::optimizer {
+
+using LogicalProperties = std::string;
+
+}  // namespace mongo::optimizer

src/mongo/db/query/optimizer/visitor.h

@@ -0,0 +1,46 @@
+/**
+ *    Copyright (C) 2020-present MongoDB, Inc.
+ *
+ *    This program is free software: you can redistribute it and/or modify
+ *    it under the terms of the Server Side Public License, version 1,
+ *    as published by MongoDB, Inc.
+ *
+ *    This program is distributed in the hope that it will be useful,
+ *    but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *    Server Side Public License for more details.
+ *
+ *    You should have received a copy of the Server Side Public License
+ *    along with this program. If not, see
+ *    <http://www.mongodb.com/licensing/server-side-public-license>.
+ *
+ *    As a special exception, the copyright holders give permission to link the
+ *    code of portions of this program with the OpenSSL library under certain
+ *    conditions as described in each individual source file and distribute
+ *    linked combinations including the program with the OpenSSL library. You
+ *    must comply with the Server Side Public License in all respects for
+ *    all of the code used other than as permitted herein. If you modify file(s)
+ *    with this exception, you may extend this exception to your version of the
+ *    file(s), but you are not obligated to do so. If you do not wish to do so,
+ *    delete this exception statement from your version. If you delete this
+ *    exception statement from all source files in the program, then also delete
+ *    it in the license file.
+ */
+
+#pragma once
+
+#include <string>
+
+namespace mongo::optimizer {
+
+class AbstractVisitor {
+public:
+    virtual void visit(ScanNode& node) = 0;
+    virtual void visit(MultiJoinNode& node) = 0;
+    virtual void visit(UnionNode& node) = 0;
+    virtual void visit(GroupByNode& node) = 0;
+    virtual void visit(UnwindNode& node) = 0;
+    virtual void visit(WindNode& node) = 0;
+};
+
+}  // namespace mongo::optimizer