Revert "SERVER-24768 Add view cycle and depth checking"

This reverts commit 30a6aeb8ec685903818051866095f773c53a842a.

5 files changed, 24 insertions, 451 deletions

diff --git a/src/mongo/db/views/SConscript b/src/mongo/db/views/SConscript
index a82c893ee0d..ee25270984c 100644
--- a/src/mongo/db/views/SConscript
+++ b/src/mongo/db/views/SConscript
@@ -21,7 +21,6 @@ env.Library(
     source=[
         'view.cpp',
         'view_catalog.cpp',
-        'view_graph.cpp',
         'resolved_view.cpp',
     ],
     LIBDEPS=[
diff --git a/src/mongo/db/views/view_catalog.cpp b/src/mongo/db/views/view_catalog.cpp
index 33cc9737ad9..fa9f73cc209 100644
--- a/src/mongo/db/views/view_catalog.cpp
+++ b/src/mongo/db/views/view_catalog.cpp
@@ -38,10 +38,6 @@
 #include "mongo/base/string_data.h"
 #include "mongo/db/namespace_string.h"
 #include "mongo/db/operation_context.h"
-#include "mongo/db/pipeline/aggregation_request.h"
-#include "mongo/db/pipeline/document_source.h"
-#include "mongo/db/pipeline/expression_context.h"
-#include "mongo/db/pipeline/pipeline.h"
 #include "mongo/db/server_parameters.h"
 #include "mongo/db/storage/recovery_unit.h"
 #include "mongo/db/views/view.h"
@@ -55,6 +51,8 @@ namespace mongo {
 ExportedServerParameter<bool, ServerParameterType::kStartupOnly> enableViewsParameter(
     ServerParameterSet::getGlobal(), "enableViews", &enableViews);
 
+const std::uint32_t ViewCatalog::kMaxViewDepth = 20;
+
 Status ViewCatalog::reloadIfNeeded(OperationContext* txn) {
     stdx::lock_guard<stdx::mutex> lk(_mutex);
     return _reloadIfNeeded_inlock(txn);
@@ -79,83 +77,24 @@ Status ViewCatalog::_reloadIfNeeded_inlock(OperationContext* txn) {
     return status;
 }
 
-Status ViewCatalog::_createOrUpdateView_inlock(OperationContext* txn,
-                                               const NamespaceString& viewName,
-                                               const NamespaceString& viewOn,
-                                               const BSONArray& pipeline) {
+void ViewCatalog::_createOrUpdateView_inlock(OperationContext* txn,
+                                             const NamespaceString& viewName,
+                                             const NamespaceString& viewOn,
+                                             const BSONArray& pipeline) {
     invariant(_valid.load());
     BSONObj viewDef =
         BSON("_id" << viewName.ns() << "viewOn" << viewOn.coll() << "pipeline" << pipeline);
+    _durable->upsert(txn, viewName, viewDef);
 
     BSONObj ownedPipeline = pipeline.getOwned();
-    auto view = std::make_shared<ViewDefinition>(
+    _viewMap[viewName.ns()] = std::make_shared<ViewDefinition>(
         viewName.db(), viewName.coll(), viewOn.coll(), ownedPipeline);
-
-    // Check that the resulting dependency graph is acyclic and within the maximum depth.
-    Status graphStatus = _upsertIntoGraph(txn, *(view.get()));
-    if (!graphStatus.isOK()) {
-        return graphStatus;
-    }
-
-    _durable->upsert(txn, viewName, viewDef);
-    _viewMap[viewName.ns()] = view;
-    txn->recoveryUnit()->onRollback([this, viewName]() {
-        this->_viewMap.erase(viewName.ns());
-        this->_viewGraphNeedsRefresh = true;
-    });
+    txn->recoveryUnit()->onRollback([this, viewName]() { this->_viewMap.erase(viewName.ns()); });
 
     // We may get invalidated, but we're exclusively locked, so the change must be ours.
     txn->recoveryUnit()->onCommit([this]() { this->_valid.store(true); });
-    return Status::OK();
 }
 
-Status ViewCatalog::_upsertIntoGraph(OperationContext* txn, const ViewDefinition& viewDef) {
-
-    // Performs the insert into the graph.
-    auto doInsert = [this, &txn](const ViewDefinition& viewDef, bool needsValidation) -> Status {
-        // Parse the pipeline for this view to get the namespaces it references.
-        AggregationRequest request(viewDef.viewOn(), viewDef.pipeline());
-        boost::intrusive_ptr<ExpressionContext> expCtx = new ExpressionContext(txn, request);
-        auto pipelineStatus = Pipeline::parse(viewDef.pipeline(), expCtx);
-        if (!pipelineStatus.isOK()) {
-            uassert(40255,
-                    str::stream() << "Invalid pipeline for existing view " << viewDef.name().ns()
-                                  << "; "
-                                  << pipelineStatus.getStatus().reason(),
-                    !needsValidation);
-            return pipelineStatus.getStatus();
-        }
-
-        std::vector<NamespaceString> refs = pipelineStatus.getValue()->getInvolvedCollections();
-        refs.push_back(viewDef.viewOn());
-
-        if (needsValidation) {
-            return _viewGraph.insertAndValidate(viewDef.name(), refs);
-        } else {
-            _viewGraph.insertWithoutValidating(viewDef.name(), refs);
-            return Status::OK();
-        }
-    };
-
-    if (_viewGraphNeedsRefresh) {
-        _viewGraph.clear();
-        for (auto&& iter : _viewMap) {
-            auto status = doInsert(*(iter.second.get()), false);
-            // If we cannot fully refresh the graph, we will keep '_viewGraphNeedsRefresh' true.
-            if (!status.isOK()) {
-                return status;
-            }
-        }
-        // Only if the inserts completed without error will we no longer need a refresh.
-        _viewGraphNeedsRefresh = false;
-    }
-
-    // Remove the view definition first in case this is an update. If it is not in the graph, it
-    // is simply a no-op.
-    _viewGraph.remove(viewDef.name());
-
-    return doInsert(viewDef, true);
-}
 
 Status ViewCatalog::createView(OperationContext* txn,
                                const NamespaceString& viewName,
@@ -177,7 +116,10 @@ Status ViewCatalog::createView(OperationContext* txn,
         return Status(ErrorCodes::InvalidNamespace,
                       str::stream() << "invalid name for 'viewOn': " << viewOn.coll());
 
-    return _createOrUpdateView_inlock(txn, viewName, viewOn, pipeline);
+    // TODO(SERVER-24768): Need to ensure view is correct and doesn't introduce a cycle.
+
+    _createOrUpdateView_inlock(txn, viewName, viewOn, pipeline);
+    return Status::OK();
 }
 
 Status ViewCatalog::modifyView(OperationContext* txn,
@@ -190,8 +132,7 @@ Status ViewCatalog::modifyView(OperationContext* txn,
         return Status(ErrorCodes::BadValue,
                       "View must be created on a view or collection in the same database");
 
-    ViewDefinition* viewPtr = _lookup_inlock(txn, viewName.ns());
-    if (!viewPtr)
+    if (!_lookup_inlock(txn, StringData(viewName.ns())))
         return Status(ErrorCodes::NamespaceNotFound,
                       str::stream() << "cannot modify missing view " << viewName.ns());
 
@@ -199,11 +140,8 @@ Status ViewCatalog::modifyView(OperationContext* txn,
         return Status(ErrorCodes::InvalidNamespace,
                       str::stream() << "invalid name for 'viewOn': " << viewOn.coll());
 
-    ViewDefinition savedDefinition = *viewPtr;
-    txn->recoveryUnit()->onRollback([this, txn, viewName, savedDefinition]() {
-        this->_viewMap[viewName.ns()] = std::make_shared<ViewDefinition>(savedDefinition);
-    });
-    return _createOrUpdateView_inlock(txn, viewName, viewOn, pipeline);
+    _createOrUpdateView_inlock(txn, viewName, viewOn, pipeline);
+    return Status::OK();
 }
 
 Status ViewCatalog::dropView(OperationContext* txn, const NamespaceString& viewName) {
@@ -220,10 +158,8 @@ Status ViewCatalog::dropView(OperationContext* txn, const NamespaceString& viewN
 
     invariant(_valid.load());
     _durable->remove(txn, viewName);
-    _viewGraph.remove(savedDefinition.name());
     _viewMap.erase(viewName.ns());
-    txn->recoveryUnit()->onRollback([this, txn, viewName, savedDefinition]() {
-        this->_viewGraphNeedsRefresh = true;
+    txn->recoveryUnit()->onRollback([this, viewName, savedDefinition]() {
         this->_viewMap[viewName.ns()] = std::make_shared<ViewDefinition>(savedDefinition);
     });
 
@@ -252,7 +188,7 @@ StatusWith<ResolvedView> ViewCatalog::resolveView(OperationContext* txn,
     const NamespaceString* resolvedNss = &nss;
     std::vector<BSONObj> resolvedPipeline;
 
-    for (int i = 0; i < ViewGraph::kMaxViewDepth; i++) {
+    for (std::uint32_t i = 0; i < ViewCatalog::kMaxViewDepth; i++) {
         ViewDefinition* view = _lookup_inlock(txn, resolvedNss->ns());
         if (!view)
             return StatusWith<ResolvedView>({*resolvedNss, resolvedPipeline});
@@ -271,6 +207,6 @@ StatusWith<ResolvedView> ViewCatalog::resolveView(OperationContext* txn,
 
     return {ErrorCodes::ViewDepthLimitExceeded,
             str::stream() << "View depth too deep or view cycle detected; maximum depth is "
-                          << ViewGraph::kMaxViewDepth};
+                          << kMaxViewDepth};
 }
 }  // namespace mongo
diff --git a/src/mongo/db/views/view_catalog.h b/src/mongo/db/views/view_catalog.h
index 8dadf38c1c1..e96278c8ce9 100644
--- a/src/mongo/db/views/view_catalog.h
+++ b/src/mongo/db/views/view_catalog.h
@@ -41,7 +41,6 @@
 #include "mongo/db/views/durable_view_catalog.h"
 #include "mongo/db/views/resolved_view.h"
 #include "mongo/db/views/view.h"
-#include "mongo/db/views/view_graph.h"
 #include "mongo/stdx/mutex.h"
 #include "mongo/util/string_map.h"
 
@@ -58,6 +57,7 @@ class ViewCatalog {
 public:
     // TODO(SERVER-23700): Make this a unique_ptr once StringMap supports move-only types.
     using ViewMap = StringMap<std::shared_ptr<ViewDefinition>>;
+    static const std::uint32_t kMaxViewDepth;
 
     explicit ViewCatalog(DurableViewCatalog* durable) : _durable(durable) {}
 
@@ -133,19 +133,13 @@ public:
      */
     void invalidate() {
         _valid.store(false);
-        _viewGraphNeedsRefresh = true;
     }
 
 private:
-    Status _createOrUpdateView_inlock(OperationContext* txn,
-                                      const NamespaceString& viewName,
-                                      const NamespaceString& viewOn,
-                                      const BSONArray& pipeline);
-    /**
-     * Parses the view definition pipeline, attempts to upsert into the view graph, and refreshes
-     * the graph if necessary. Returns an error status if the resulting graph would be invalid.
-     */
-    Status _upsertIntoGraph(OperationContext* txn, const ViewDefinition& viewDef);
+    void _createOrUpdateView_inlock(OperationContext* txn,
+                                    const NamespaceString& viewName,
+                                    const NamespaceString& viewOn,
+                                    const BSONArray& pipeline);
 
     ViewDefinition* _lookup_inlock(OperationContext* txn, StringData ns);
     Status _reloadIfNeeded_inlock(OperationContext* txn);
@@ -154,7 +148,5 @@ private:
     ViewMap _viewMap;
     DurableViewCatalog* _durable;
     AtomicBool _valid;
-    ViewGraph _viewGraph;
-    bool _viewGraphNeedsRefresh = true;  // Defers initializing the graph until the first insert.
 };
 }  // namespace mongo
diff --git a/src/mongo/db/views/view_graph.cpp b/src/mongo/db/views/view_graph.cpp
deleted file mode 100644
index 27a19a9fbcd..00000000000
--- a/src/mongo/db/views/view_graph.cpp
+++ /dev/null
@@ -1,221 +0,0 @@
-/**
-*    Copyright (C) 2016 MongoDB Inc.
-*
-*    This program is free software: you can redistribute it and/or  modify
-*    it under the terms of the GNU Affero General Public License, version 3,
-*    as published by the Free Software Foundation.
-*
-*    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
-*    GNU Affero General Public License for more details.
-*
-*    You should have received a copy of the GNU Affero General Public License
-*    along with this program.  If not, see <http://www.gnu.org/licenses/>.
-*
-*    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 GNU Affero General 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/platform/basic.h"
-
-#include "mongo/db/views/view_graph.h"
-
-#include "mongo/db/views/view.h"
-
-namespace mongo {
-
-const int ViewGraph::kMaxViewDepth = 20;
-uint64_t ViewGraph::_idCounter = 0;
-
-void ViewGraph::clear() {
-    _graph.clear();
-    _namespaceIds.clear();
-}
-
-Status ViewGraph::insertAndValidate(const NamespaceString& viewNss,
-                                    const std::vector<NamespaceString>& refs) {
-    insertWithoutValidating(viewNss, refs);
-
-    // Perform validation on this newly inserted view. Note, if the graph was put in an invalid
-    // state through unvalidated inserts (e.g. if the user manually edits system.views)
-    // this may not necessarily be detected. We only check for errors introduced by this view.
-    uint64_t nodeId = _getNodeId(viewNss);
-
-    auto viewDepthLimitExceeded = [this, &viewNss]() -> Status {
-        this->remove(viewNss);
-        return Status(ErrorCodes::ViewDepthLimitExceeded,
-                      str::stream() << "View depth limit exceeded; maximum depth is "
-                                    << kMaxViewDepth);
-    };
-
-    // Check for cycles and get the height of the children.
-    HeightMap heightMap;
-    std::vector<uint64_t> cycleVertices;
-    ErrorCodes::Error childRes =
-        _getChildrenHeightAndCheckCycle(nodeId, nodeId, 0, &heightMap, &cycleVertices);
-    if (childRes == ErrorCodes::ViewDepthLimitExceeded) {
-        return viewDepthLimitExceeded();
-    } else if (childRes == ErrorCodes::GraphContainsCycle) {
-        // Make the error message with the namespaces of the cycle and remove the node.
-        str::stream ss;
-        ss << "View cycle detected: ";
-        for (auto cycleIter = cycleVertices.rbegin(); cycleIter != cycleVertices.rend();
-             cycleIter++) {
-            ss << _graph[*cycleIter].ns << " => ";
-        }
-        ss << viewNss.ns();
-        remove(viewNss);
-        return Status(ErrorCodes::GraphContainsCycle, ss);
-    }
-
-    // Subtract one since the child height includes the non-view leaf node(s).
-    int childrenHeight = heightMap[nodeId].height - 1;
-
-    // Get the height of the parents to obtain the diameter through this node.
-    heightMap.clear();
-    ErrorCodes::Error parentRes = _getParentsHeight(nodeId, 0, &heightMap);
-    if (parentRes == ErrorCodes::ViewDepthLimitExceeded) {
-        return viewDepthLimitExceeded();
-    }
-
-    // Check the combined heights of the children and parents.
-    int parentsHeight = heightMap[nodeId].height;
-    // Subtract one since the parent and children heights include the current node.
-    int diameter = parentsHeight + childrenHeight - 1;
-
-    if (diameter > kMaxViewDepth) {
-        return viewDepthLimitExceeded();
-    }
-
-    return Status::OK();
-}
-
-void ViewGraph::insertWithoutValidating(const NamespaceString& viewNss,
-                                        const std::vector<NamespaceString>& refs) {
-    uint64_t nodeId = _getNodeId(viewNss);
-    // Note, the parent pointers of this node are set when the parents are inserted.
-    // This sets the name and children pointers of the node for this view, as well as the parent
-    // pointers for its children.
-    Node* node = &(_graph[nodeId]);
-    invariant(node->children.empty());
-    node->ns = viewNss.ns();
-
-    for (const NamespaceString& childNss : refs) {
-        uint64_t childId = _getNodeId(childNss);
-        node->children.insert(childId);
-        _graph[childId].parents.insert(nodeId);
-    }
-}
-
-void ViewGraph::remove(const NamespaceString& viewNss) {
-    uint64_t nodeId = _getNodeId(viewNss);
-    Node* node = &(_graph[nodeId]);
-
-    // Remove self-reference pointers if they exist.
-    node->children.erase(nodeId);
-    node->parents.erase(nodeId);
-
-    // Remove child->parent pointers.
-    for (uint64_t childId : node->children) {
-        Node* childNode = &(_graph[childId]);
-        childNode->parents.erase(nodeId);
-        // If the child has no remaining references or children, remove it.
-        if (childNode->parents.size() == 0 && childNode->children.size() == 0) {
-            _graph.erase(childId);
-            _namespaceIds.erase(childNode->ns);
-        }
-    }
-
-    // Remove all child pointers since this view no longer references anything.
-    node->children.clear();
-
-    // Only remove node if there are no remaining references to this node.
-    if (node->parents.size() == 0) {
-        _graph.erase(nodeId);
-        _namespaceIds.erase(node->ns);
-    }
-}
-
-ErrorCodes::Error ViewGraph::_getParentsHeight(uint64_t currentId,
-                                               int currentDepth,
-                                               HeightMap* heightMap) {
-    const Node& currentNode = _graph[currentId];
-    int maxHeightOfParents = 0;
-
-    // Return early if we've already exceeded the maximum depth. This will also be triggered if
-    // we're traversing a cycle introduced through unvalidated inserts.
-    if (currentDepth > kMaxViewDepth) {
-        return ErrorCodes::ViewDepthLimitExceeded;
-    }
-
-    for (uint64_t parentId : currentNode.parents) {
-        if (!(*heightMap)[parentId].checked) {
-            auto res = _getParentsHeight(parentId, currentDepth + 1, heightMap);
-            if (res != ErrorCodes::OK) {
-                return res;
-            }
-        }
-        maxHeightOfParents = std::max(maxHeightOfParents, (*heightMap)[parentId].height);
-    }
-
-    (*heightMap)[currentId].checked = true;
-    (*heightMap)[currentId].height = maxHeightOfParents + 1;
-
-    return ErrorCodes::OK;
-}
-
-ErrorCodes::Error ViewGraph::_getChildrenHeightAndCheckCycle(uint64_t startingId,
-                                                             uint64_t currentId,
-                                                             int currentDepth,
-                                                             HeightMap* heightMap,
-                                                             std::vector<uint64_t>* cycleIds) {
-    // Check children of current node.
-    const Node& currentNode = _graph[currentId];
-    if (currentDepth > 0 && currentId == startingId) {
-        return ErrorCodes::GraphContainsCycle;
-    }
-
-    // Return early if we've already exceeded the maximum depth. This will also be triggered if
-    // we're traversing a cycle introduced through unvalidated inserts.
-    if (currentDepth > kMaxViewDepth) {
-        return ErrorCodes::ViewDepthLimitExceeded;
-    }
-
-    int maxHeightOfChildren = 0;
-    for (uint64_t childId : currentNode.children) {
-        if (!(*heightMap)[childId].checked) {
-            auto res = _getChildrenHeightAndCheckCycle(
-                startingId, childId, currentDepth + 1, heightMap, cycleIds);
-            if (res == ErrorCodes::GraphContainsCycle) {
-                cycleIds->push_back(currentId);
-                return res;
-            } else if (res != ErrorCodes::OK) {
-                return res;
-            }
-        }
-        maxHeightOfChildren = std::max(maxHeightOfChildren, (*heightMap)[childId].height);
-    }
-
-    (*heightMap)[currentId].checked = true;
-    (*heightMap)[currentId].height = maxHeightOfChildren + 1;
-    return ErrorCodes::OK;
-}
-
-uint64_t ViewGraph::_getNodeId(const NamespaceString& nss) {
-    if (_namespaceIds.find(nss.ns()) == _namespaceIds.end()) {
-        _namespaceIds[nss.ns()] = _idCounter++;
-    }
-    return _namespaceIds[nss.ns()];
-}
-
-}  // namespace mongo
diff --git a/src/mongo/db/views/view_graph.h b/src/mongo/db/views/view_graph.h
deleted file mode 100644
index 20214444d2c..00000000000
--- a/src/mongo/db/views/view_graph.h
+++ /dev/null
@@ -1,133 +0,0 @@
-/**
-*    Copyright (C) 2016 MongoDB Inc.
-*
-*    This program is free software: you can redistribute it and/or  modify
-*    it under the terms of the GNU Affero General Public License, version 3,
-*    as published by the Free Software Foundation.
-*
-*    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
-*    GNU Affero General Public License for more details.
-*
-*    You should have received a copy of the GNU Affero General Public License
-*    along with this program.  If not, see <http://www.gnu.org/licenses/>.
-*
-*    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 GNU Affero General 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 <unordered_map>
-#include <unordered_set>
-#include <vector>
-
-#include "mongo/base/status.h"
-#include "mongo/db/namespace_string.h"
-#include "mongo/util/string_map.h"
-
-namespace mongo {
-class ViewDefinition;
-
-/**
- * Validates that the graph of view dependencies is acyclic and within the allowed depth.
- * Each node is represented by an integer id, and stores integer ids for its parents and children
- * in the graph.
- *
- * This is owned and managed by the ViewCatalog.
- */
-class ViewGraph {
-    MONGO_DISALLOW_COPYING(ViewGraph);
-
-public:
-    static const int kMaxViewDepth;
-
-    ViewGraph() = default;
-
-    /**
-     * Called when a view is added to the catalog. 'refs' are a list of namespaces that the view
-     * represented by 'viewNss' references in its viewOn or pipeline. Checks if this view introduces
-     * a cycle or max diameter. If an error is detected, it will not insert.
-     */
-    Status insertAndValidate(const NamespaceString& viewNss,
-                             const std::vector<NamespaceString>& refs);
-
-    /**
-     * Called when view definitions are being reloaded from the catalog (e.g. on restart of mongod).
-     * Does the same as insertAndValidate except does not check for cycles or max diameter.
-     */
-    void insertWithoutValidating(const NamespaceString& viewNss,
-                                 const std::vector<NamespaceString>& refs);
-
-    /**
-     * Called when a view is removed from the catalog. If the view does not exist in the graph it is
-     * a no-op. The view may also have a cycle or max diameter through it.
-     */
-    void remove(const NamespaceString& viewNss);
-
-    /**
-     * Deletes the view graph and all references to namespaces.
-     */
-    void clear();
-
-private:
-    // A graph node represents a namespace. The parent-child relation is defined as a parent
-    // references the child either through viewOn or in $lookup/$graphLookup/$facet in its pipeline.
-    // E.g. the command {create: "a", viewOn: "b", pipeline: [{$lookup: {from: "c"}}]}
-    // means the node for "a" is a parent of nodes for "b" and "c" since it references them.
-    struct Node {
-        // Note, a view may refer to the same child more than once, but we only need to know the
-        // set of children and parents, since we do not need to traverse duplicates.
-        std::unordered_set<uint64_t> parents;
-        std::unordered_set<uint64_t> children;
-        std::string ns;
-    };
-
-    // Bookkeeping for graph traversals.
-    struct NodeHeight {
-        bool checked = false;
-        int height = 0;
-    };
-
-    using HeightMap = std::unordered_map<uint64_t, NodeHeight>;
-
-    /**
-     * Recursively traverses parents of this node and computes their heights. Returns an error
-     * if the maximum depth is exceeded.
-     */
-    ErrorCodes::Error _getParentsHeight(uint64_t currentId, int currentDepth, HeightMap* heightMap);
-
-    /**
-     * Recursively traverses children of the starting node and computes their heights. Returns an
-     * error if the maximum depth is exceeded or a cycle is detected through the starting node.
-     */
-    ErrorCodes::Error _getChildrenHeightAndCheckCycle(uint64_t startingId,
-                                                      uint64_t currentId,
-                                                      int currentDepth,
-                                                      HeightMap* heightMap,
-                                                      std::vector<uint64_t>* cycleIds);
-
-    /**
-     * Gets the id for this namespace, and creates an id if it doesn't exist.
-     */
-    uint64_t _getNodeId(const NamespaceString& ns);
-
-    // Maps namespaces to an internal node id. A mapping exists for every namespace referenced,
-    // i.e. existing views, collections, and non-existing namespaces.
-    StringMap<uint64_t> _namespaceIds;
-
-    // Maps node ids to nodes. There is a 1-1 correspondance with _namespaceIds, hence the lifetime
-    // of a node is the same as the lifetime as its corresponding node id.
-    std::unordered_map<uint64_t, Node> _graph;
-    static uint64_t _idCounter;
-};
-}  // namespace mongo