Update upstream source from tag 'upstream/6.0.0'master

Update to upstream version '6.0.0'
with Debian dir 5604a80ec1c96ca76f25f40d78e6ef855abec322

8 files changed, 95 insertions, 204 deletions

diff --git a/src/mongo/db/views/SConscript b/src/mongo/db/views/SConscript
index 94d6b3edd39..a16bf79890a 100644
--- a/src/mongo/db/views/SConscript
+++ b/src/mongo/db/views/SConscript
@@ -17,7 +17,6 @@ env.Library(
         '$BUILD_DIR/mongo/db/audit',
         '$BUILD_DIR/mongo/db/catalog/database_holder',
         '$BUILD_DIR/mongo/db/multitenancy',
-        '$BUILD_DIR/mongo/db/views/view_catalog_helpers',
     ],
 )
 
diff --git a/src/mongo/db/views/durable_view_catalog.cpp b/src/mongo/db/views/durable_view_catalog.cpp
index e5281a8c63c..c96b7af6672 100644
--- a/src/mongo/db/views/durable_view_catalog.cpp
+++ b/src/mongo/db/views/durable_view_catalog.cpp
@@ -47,7 +47,6 @@
 #include "mongo/db/operation_context.h"
 #include "mongo/db/storage/record_data.h"
 #include "mongo/db/tenant_database_name.h"
-#include "mongo/db/views/view_catalog_helpers.h"
 #include "mongo/logv2/log.h"
 #include "mongo/stdx/unordered_set.h"
 #include "mongo/util/assert_util.h"
@@ -55,57 +54,6 @@
 
 namespace mongo {
 
-namespace {
-void validateViewDefinitionBSON(OperationContext* opCtx,
-                                const BSONObj& viewDefinition,
-                                StringData dbName) {
-    // Internal callers should always pass in a valid 'dbName' against which to compare the
-    // 'viewDefinition'.
-    invariant(NamespaceString::validDBName(dbName));
-
-    bool valid = true;
-
-    for (const BSONElement& e : viewDefinition) {
-        std::string name(e.fieldName());
-        valid &= name == "_id" || name == "viewOn" || name == "pipeline" || name == "collation" ||
-            name == "timeseries";
-    }
-
-    const auto viewName = viewDefinition["_id"].str();
-    const auto viewNameIsValid = NamespaceString::validCollectionComponent(viewName) &&
-        NamespaceString::validDBName(nsToDatabaseSubstring(viewName));
-    valid &= viewNameIsValid;
-
-    // Only perform validation via NamespaceString if the collection name has been determined to
-    // be valid. If not valid then the NamespaceString constructor will uassert.
-    if (viewNameIsValid) {
-        NamespaceString viewNss(viewName);
-        valid &= viewNss.isValid() && viewNss.db() == dbName;
-    }
-
-    valid &= NamespaceString::validCollectionName(viewDefinition["viewOn"].str());
-
-    const bool hasPipeline = viewDefinition.hasField("pipeline");
-    valid &= hasPipeline;
-    if (hasPipeline) {
-        valid &= viewDefinition["pipeline"].type() == mongo::Array;
-    }
-
-    valid &= (!viewDefinition.hasField("collation") ||
-              viewDefinition["collation"].type() == BSONType::Object);
-
-    valid &= !viewDefinition.hasField("timeseries") ||
-        viewDefinition["timeseries"].type() == BSONType::Object;
-
-    uassert(ErrorCodes::InvalidViewDefinition,
-            str::stream() << "found invalid view definition " << viewDefinition["_id"]
-                          << " while reading '"
-                          << NamespaceString(dbName, NamespaceString::kSystemDotViewsCollectionName)
-                          << "'",
-            valid);
-}
-}  // namespace
-
 // DurableViewCatalog
 
 void DurableViewCatalog::onExternalChange(OperationContext* opCtx, const NamespaceString& name) {
@@ -120,30 +68,6 @@ void DurableViewCatalog::onExternalChange(OperationContext* opCtx, const Namespa
     catalog->reloadViews(opCtx, name.db()).ignore();
 }
 
-Status DurableViewCatalog::onExternalInsert(OperationContext* opCtx,
-                                            const BSONObj& doc,
-                                            const NamespaceString& name) {
-    try {
-        validateViewDefinitionBSON(opCtx, doc, name.db());
-    } catch (const DBException& e) {
-        return e.toStatus();
-    }
-
-    auto catalog = CollectionCatalog::get(opCtx);
-    NamespaceString viewName(doc.getStringField("_id"));
-    NamespaceString viewOn(name.db(), doc.getStringField("viewOn"));
-    BSONArray pipeline(doc.getObjectField("pipeline"));
-    BSONObj collation(doc.getObjectField("collation"));
-
-    return catalog->createView(opCtx,
-                               viewName,
-                               viewOn,
-                               pipeline,
-                               collation,
-                               view_catalog_helpers::validatePipeline,
-                               CollectionCatalog::ViewUpsertMode::kAlreadyDurableView);
-}
-
 void DurableViewCatalog::onSystemViewsCollectionDrop(OperationContext* opCtx,
                                                      const NamespaceString& name) {
     dassert(opCtx->lockState()->isDbLockedForMode(name.db(), MODE_IX));
@@ -203,9 +127,9 @@ void DurableViewCatalogImpl::_iterate(OperationContext* opCtx,
         try {
             viewDefinition = _validateViewDefinition(opCtx, record->data);
             uassertStatusOK(callback(viewDefinition));
-        } catch (const ExceptionFor<ErrorCodes::InvalidViewDefinition>&) {
+        } catch (const ExceptionFor<ErrorCodes::InvalidViewDefinition>& ex) {
             if (lookupBehavior == ViewCatalogLookupBehavior::kValidateViews) {
-                throw;
+                throw ex;
             }
         }
     }
@@ -218,9 +142,46 @@ BSONObj DurableViewCatalogImpl::_validateViewDefinition(OperationContext* opCtx,
     // decimal data even if decimal is disabled.
     fassert(40224, validateBSON(recordData.data(), recordData.size()));
     BSONObj viewDefinition = recordData.toBson();
-    std::string dbName(_db->name().dbName());
 
-    validateViewDefinitionBSON(opCtx, viewDefinition, dbName);
+    bool valid = true;
+
+    for (const BSONElement& e : viewDefinition) {
+        std::string name(e.fieldName());
+        valid &= name == "_id" || name == "viewOn" || name == "pipeline" || name == "collation" ||
+            name == "timeseries";
+    }
+
+    const auto viewName = viewDefinition["_id"].str();
+    const auto viewNameIsValid = NamespaceString::validCollectionComponent(viewName) &&
+        NamespaceString::validDBName(nsToDatabaseSubstring(viewName));
+    valid &= viewNameIsValid;
+
+    // Only perform validation via NamespaceString if the collection name has been determined to
+    // be valid. If not valid then the NamespaceString constructor will uassert.
+    if (viewNameIsValid) {
+        NamespaceString viewNss(viewName);
+        valid &= viewNss.isValid() && viewNss.db() == _db->name().dbName();
+    }
+
+    valid &= NamespaceString::validCollectionName(viewDefinition["viewOn"].str());
+
+    const bool hasPipeline = viewDefinition.hasField("pipeline");
+    valid &= hasPipeline;
+    if (hasPipeline) {
+        valid &= viewDefinition["pipeline"].type() == mongo::Array;
+    }
+
+    valid &= (!viewDefinition.hasField("collation") ||
+              viewDefinition["collation"].type() == BSONType::Object);
+
+    valid &= !viewDefinition.hasField("timeseries") ||
+        viewDefinition["timeseries"].type() == BSONType::Object;
+
+    uassert(ErrorCodes::InvalidViewDefinition,
+            str::stream() << "found invalid view definition " << viewDefinition["_id"]
+                          << " while reading '" << _db->getSystemViewsName() << "'",
+            valid);
+
     return viewDefinition;
 }
 
diff --git a/src/mongo/db/views/durable_view_catalog.h b/src/mongo/db/views/durable_view_catalog.h
index 6b938c6f54c..0546636225d 100644
--- a/src/mongo/db/views/durable_view_catalog.h
+++ b/src/mongo/db/views/durable_view_catalog.h
@@ -68,14 +68,6 @@ public:
     static void onExternalChange(OperationContext* opCtx, const NamespaceString& name);
 
     /**
-     * Thread-safe method to insert into the in-memory view catalog when there is an insert to
-     * 'system.views'.
-     */
-    static Status onExternalInsert(OperationContext* opCtx,
-                                   const BSONObj& doc,
-                                   const NamespaceString& name);
-
-    /**
      * Thread-safe method to clear the in-memory state of the view catalog when the 'system.views'
      * collection is dropped.
      */
diff --git a/src/mongo/db/views/resolved_view.cpp b/src/mongo/db/views/resolved_view.cpp
index 6795a874968..244d38a0b55 100644
--- a/src/mongo/db/views/resolved_view.cpp
+++ b/src/mongo/db/views/resolved_view.cpp
@@ -33,7 +33,6 @@
 
 #include "mongo/base/init.h"
 #include "mongo/bson/bsonobjbuilder.h"
-#include "mongo/db/pipeline/document_source_coll_stats.h"
 #include "mongo/db/pipeline/document_source_index_stats.h"
 #include "mongo/db/pipeline/document_source_internal_convert_bucket_index_stats.h"
 #include "mongo/db/pipeline/document_source_internal_unpack_bucket.h"
@@ -92,22 +91,11 @@ ResolvedView ResolvedView::fromBSON(const BSONObj& commandResponseObj) {
         mixedSchema = boost::optional<bool>(mixedSchemaElem.boolean());
     }
 
-    boost::optional<bool> usesExtendedRange = boost::none;
-    if (auto usesExtendedRangeElem = viewDef[kTimeseriesUsesExtendedRange]) {
-        uassert(6646910,
-                str::stream() << "view definition must have " << kTimeseriesUsesExtendedRange
-                              << " of type bool or no such field",
-                usesExtendedRangeElem.type() == BSONType::Bool);
-
-        usesExtendedRange = boost::optional<bool>(usesExtendedRangeElem.boolean());
-    }
-
     return {NamespaceString(viewDef["ns"].valueStringData()),
             std::move(pipeline),
             std::move(collationSpec),
             std::move(timeseriesOptions),
-            std::move(mixedSchema),
-            std::move(usesExtendedRange)};
+            std::move(mixedSchema)};
 }
 
 void ResolvedView::serialize(BSONObjBuilder* builder) const {
@@ -121,10 +109,6 @@ void ResolvedView::serialize(BSONObjBuilder* builder) const {
     // Only serialize if it doesn't contain mixed data.
     if ((_timeseriesMayContainMixedData && !(*_timeseriesMayContainMixedData)))
         subObj.append(kTimeseriesMayContainMixedData, *_timeseriesMayContainMixedData);
-
-    if ((_timeseriesUsesExtendedRange && (*_timeseriesUsesExtendedRange)))
-        subObj.append(kTimeseriesUsesExtendedRange, *_timeseriesUsesExtendedRange);
-
     if (!_defaultCollation.isEmpty()) {
         subObj.append("collation", _defaultCollation);
     }
@@ -134,48 +118,46 @@ std::shared_ptr<const ErrorExtraInfo> ResolvedView::parse(const BSONObj& cmdRepl
     return std::make_shared<ResolvedView>(fromBSON(cmdReply));
 }
 
-void ResolvedView::handleTimeseriesRewrites(std::vector<BSONObj>* resolvedPipeline) const {
-    // Stages that are constrained to be the first stage of the pipeline ($collStats, $indexStats)
-    // require special handling since $_internalUnpackBucket is the first stage.
-    if (resolvedPipeline->size() >= 2 &&
-        (*resolvedPipeline)[0][DocumentSourceInternalUnpackBucket::kStageNameInternal] &&
-        ((*resolvedPipeline)[1][DocumentSourceIndexStats::kStageName] ||
-         (*resolvedPipeline)[1][DocumentSourceCollStats::kStageName])) {
-        //  Normally for a regular read, $_internalUnpackBucket unpacks the buckets entries into
-        //  time-series document format and then passes the time-series documents on through the
-        //  pipeline. Instead, for $indexStats, we need to read the buckets collection's index
-        //  stats unmodified and then pass the results through an additional stage to specially
-        //  convert them to the time-series collection's schema, and then onward. We grab the
-        //  $_internalUnpackBucket stage's time-series collection schema options and pass them
-        //  into the $_internalConvertBucketIndexStats stage to use for schema conversion.
-        if ((*resolvedPipeline)[1][DocumentSourceIndexStats::kStageName]) {
-            auto unpackStage = (*resolvedPipeline)[0];
-            (*resolvedPipeline)[0] = (*resolvedPipeline)[1];
-            BSONObjBuilder builder;
-            for (const auto& elem :
-                 unpackStage[DocumentSourceInternalUnpackBucket::kStageNameInternal].Obj()) {
-                if (elem.fieldNameStringData() == timeseries::kTimeFieldName ||
-                    elem.fieldNameStringData() == timeseries::kMetaFieldName) {
-                    builder.append(elem);
-                }
-            }
-            (*resolvedPipeline)[1] =
-                BSON(DocumentSourceInternalConvertBucketIndexStats::kStageName << builder.obj());
-        } else {
-            auto collStatsStage = (*resolvedPipeline)[1];
-            BSONObjBuilder builder;
-            for (const auto& elem : collStatsStage[DocumentSourceCollStats::kStageName].Obj()) {
+AggregateCommandRequest ResolvedView::asExpandedViewAggregation(
+    const AggregateCommandRequest& request) const {
+    // Perform the aggregation on the resolved namespace.  The new pipeline consists of two parts:
+    // first, 'pipeline' in this ResolvedView; then, the pipeline in 'request'.
+    std::vector<BSONObj> resolvedPipeline;
+    resolvedPipeline.reserve(_pipeline.size() + request.getPipeline().size());
+    resolvedPipeline.insert(resolvedPipeline.end(), _pipeline.begin(), _pipeline.end());
+    resolvedPipeline.insert(
+        resolvedPipeline.end(), request.getPipeline().begin(), request.getPipeline().end());
+
+    // $indexStats needs special handling for time-series-collections. Normally for a regular read,
+    // $_internalUnpackBucket unpacks the buckets entries into time-series document format and then
+    // passes the time-series documents on through the pipeline. Instead we need to read the buckets
+    // collection's index stats unmodified and then pass the results through an additional stage to
+    // specially convert them to the time-series collection's schema, and then onward. There is no
+    // need for the $_internalUnpackBucket stage with $indexStats, so we remove it.
+    if (resolvedPipeline.size() >= 2 &&
+        resolvedPipeline[0][DocumentSourceInternalUnpackBucket::kStageNameInternal] &&
+        resolvedPipeline[1][DocumentSourceIndexStats::kStageName]) {
+        // Clear the $_internalUnpackBucket stage.
+        auto unpackStage = resolvedPipeline[0];
+        resolvedPipeline[0] = resolvedPipeline[1];
+
+        // Grab the $_internalUnpackBucket stage's time-series collection schema options and pass
+        // them into the $_internalConvertBucketIndexStats stage to use for schema conversion.
+        BSONObjBuilder builder;
+        for (const auto& elem :
+             unpackStage[DocumentSourceInternalUnpackBucket::kStageNameInternal].Obj()) {
+            if (elem.fieldNameStringData() == timeseries::kTimeFieldName ||
+                elem.fieldNameStringData() == timeseries::kMetaFieldName) {
                 builder.append(elem);
             }
-            builder.append("$_requestOnTimeseriesView", true);
-            (*resolvedPipeline)[1] = BSON(DocumentSourceCollStats::kStageName << builder.obj());
-            // For $collStats, we directly read the collection stats from the buckets
-            // collection, and skip $_internalUnpackBucket.
-            resolvedPipeline->erase(resolvedPipeline->begin());
         }
-    } else if (serverGlobalParams.featureCompatibility.isGreaterThanOrEqualTo(
+        resolvedPipeline[1] =
+            BSON(DocumentSourceInternalConvertBucketIndexStats::kStageName << builder.obj());
+    } else if (resolvedPipeline.size() >= 1 &&
+               resolvedPipeline[0][DocumentSourceInternalUnpackBucket::kStageNameInternal] &&
+               serverGlobalParams.featureCompatibility.isGreaterThanOrEqualTo(
                    multiversion::FeatureCompatibilityVersion::kVersion_5_2)) {
-        auto unpackStage = (*resolvedPipeline)[0];
+        auto unpackStage = resolvedPipeline[0];
 
         BSONObjBuilder builder;
         for (const auto& elem :
@@ -184,31 +166,11 @@ void ResolvedView::handleTimeseriesRewrites(std::vector<BSONObj>* resolvedPipeli
         }
         builder.append(DocumentSourceInternalUnpackBucket::kAssumeNoMixedSchemaData,
                        ((_timeseriesMayContainMixedData && !(*_timeseriesMayContainMixedData))));
-
-        builder.append(DocumentSourceInternalUnpackBucket::kUsesExtendedRange,
-                       ((_timeseriesUsesExtendedRange && *_timeseriesUsesExtendedRange)));
-
-        (*resolvedPipeline)[0] =
+        resolvedPipeline[0] =
             BSON(DocumentSourceInternalUnpackBucket::kStageNameInternal << builder.obj());
     }
-}
-
-AggregateCommandRequest ResolvedView::asExpandedViewAggregation(
-    const AggregateCommandRequest& request) const {
-    // Perform the aggregation on the resolved namespace.  The new pipeline consists of two parts:
-    // first, 'pipeline' in this ResolvedView; then, the pipeline in 'request'.
-    std::vector<BSONObj> resolvedPipeline;
-    resolvedPipeline.reserve(_pipeline.size() + request.getPipeline().size());
-    resolvedPipeline.insert(resolvedPipeline.end(), _pipeline.begin(), _pipeline.end());
-    resolvedPipeline.insert(
-        resolvedPipeline.end(), request.getPipeline().begin(), request.getPipeline().end());
-
-    if (resolvedPipeline.size() >= 1 &&
-        resolvedPipeline[0][DocumentSourceInternalUnpackBucket::kStageNameInternal]) {
-        handleTimeseriesRewrites(&resolvedPipeline);
-    }
 
-    AggregateCommandRequest expandedRequest{_namespace, std::move(resolvedPipeline)};
+    AggregateCommandRequest expandedRequest{_namespace, resolvedPipeline};
 
     if (request.getExplain()) {
         expandedRequest.setExplain(request.getExplain());
@@ -230,9 +192,6 @@ AggregateCommandRequest ResolvedView::asExpandedViewAggregation(
             }
         }
         expandedRequest.setHint(rewritten);
-
-        // JLR Possibly need to handle inappropriately forcing clustered here. Will likely be
-        // handled by removing the _id predicate, however.
     } else {
         expandedRequest.setHint(request.getHint());
     }
diff --git a/src/mongo/db/views/resolved_view.h b/src/mongo/db/views/resolved_view.h
index a68ed1d5b1e..c0b3ae3d503 100644
--- a/src/mongo/db/views/resolved_view.h
+++ b/src/mongo/db/views/resolved_view.h
@@ -48,19 +48,15 @@ public:
                  std::vector<BSONObj> pipeline,
                  BSONObj defaultCollation,
                  boost::optional<TimeseriesOptions> timeseriesOptions = boost::none,
-                 boost::optional<bool> timeseriesMayContainMixedData = boost::none,
-                 boost::optional<bool> timeseriesUsesExtendedRange = boost::none)
+                 boost::optional<bool> timeseriesMayContainMixedData = boost::none)
         : _namespace(collectionNs),
           _pipeline(std::move(pipeline)),
           _defaultCollation(std::move(defaultCollation)),
           _timeseriesOptions(timeseriesOptions),
-          _timeseriesMayContainMixedData(timeseriesMayContainMixedData),
-          _timeseriesUsesExtendedRange(timeseriesUsesExtendedRange) {}
+          _timeseriesMayContainMixedData(timeseriesMayContainMixedData) {}
 
     static ResolvedView fromBSON(const BSONObj& commandResponseObj);
 
-    void handleTimeseriesRewrites(std::vector<BSONObj>* resolvedPipeline) const;
-
     /**
      * Convert an aggregation command on a view to the equivalent command against the view's
      * underlying collection.
@@ -80,16 +76,10 @@ public:
         return _defaultCollation;
     }
 
-    bool timeseries() const {
-        return _timeseriesOptions.has_value();
-    }
-
     // ErrorExtraInfo API
     static constexpr auto code = ErrorCodes::CommandOnShardedViewNotSupportedOnMongod;
     static constexpr StringData kTimeseriesMayContainMixedData = "timeseriesMayContainMixedData"_sd;
     static constexpr StringData kTimeseriesOptions = "timeseriesOptions"_sd;
-    static constexpr StringData kTimeseriesUsesExtendedRange = "timeseriesUsesExtendedRange"_sd;
-
     void serialize(BSONObjBuilder* bob) const final;
     static std::shared_ptr<const ErrorExtraInfo> parse(const BSONObj&);
 
@@ -97,17 +87,16 @@ private:
     NamespaceString _namespace;
     std::vector<BSONObj> _pipeline;
 
-    // The default collation associated with this view. An empty object means that the default
-    // is the simple collation.
+    // The default collation associated with this view. An empty object means that the default is
+    // the simple collation.
     //
     // Currently all operations which run over a view must use the default collation. This means
-    // that operations on the view which do not specify a collation inherit the default.
-    // Operations on the view which specify any other collation fail with a user error.
+    // that operations on the view which do not specify a collation inherit the default. Operations
+    // on the view which specify any other collation fail with a user error.
     BSONObj _defaultCollation;
 
     boost::optional<TimeseriesOptions> _timeseriesOptions;
     boost::optional<bool> _timeseriesMayContainMixedData;
-    boost::optional<bool> _timeseriesUsesExtendedRange;
 };
 
 }  // namespace mongo
diff --git a/src/mongo/db/views/view_catalog_helpers.cpp b/src/mongo/db/views/view_catalog_helpers.cpp
index 04218b48ef8..018fad8437d 100644
--- a/src/mongo/db/views/view_catalog_helpers.cpp
+++ b/src/mongo/db/views/view_catalog_helpers.cpp
@@ -150,7 +150,6 @@ StatusWith<ResolvedView> resolveView(OperationContext* opCtx,
     int depth = 0;
     boost::optional<bool> mixedData = boost::none;
     boost::optional<TimeseriesOptions> tsOptions = boost::none;
-    boost::optional<bool> hasExtendedRange = boost::none;
 
     for (; depth < ViewGraph::kMaxViewDepth; depth++) {
         auto view = catalog->lookupView(opCtx, *resolvedNss);
@@ -174,8 +173,7 @@ StatusWith<ResolvedView> resolveView(OperationContext* opCtx,
                  std::move(resolvedPipeline),
                  collation ? std::move(collation.get()) : CollationSpec::kSimpleSpec,
                  tsOptions,
-                 mixedData,
-                 hasExtendedRange});
+                 mixedData});
         }
 
         resolvedNss = &view->viewOn();
@@ -195,7 +193,6 @@ StatusWith<ResolvedView> resolveView(OperationContext* opCtx,
             if (tsCollection) {
                 mixedData = tsCollection->getTimeseriesBucketsMayHaveMixedSchemaData();
                 tsOptions = tsCollection->getTimeseriesOptions();
-                hasExtendedRange = tsCollection->getRequiresTimeseriesExtendedRangeSupport();
             }
         }
 
diff --git a/src/mongo/db/views/view_graph.cpp b/src/mongo/db/views/view_graph.cpp
index 716dd4e9d32..4282a0469a4 100644
--- a/src/mongo/db/views/view_graph.cpp
+++ b/src/mongo/db/views/view_graph.cpp
@@ -126,9 +126,10 @@ void ViewGraph::insertWithoutValidating(const ViewDefinition& view,
     // pointers for its children.
     Node* node = &(_graph[nodeId]);
     invariant(node->children.empty());
+    invariant(!static_cast<bool>(node->collator));
 
     node->size = pipelineSize;
-    node->collator = CollatorInterface::cloneCollator(view.defaultCollator());
+    node->collator = view.defaultCollator();
 
     for (const NamespaceString& childNss : refs) {
         uint64_t childId = _getNodeId(childNss);
@@ -164,7 +165,7 @@ void ViewGraph::remove(const NamespaceString& viewNss) {
     // This node no longer represents a view, so its children must be cleared and its collator
     // unset.
     node->children.clear();
-    node->collator = nullptr;
+    node->collator = boost::none;
 
     // Only remove node if there are no remaining references to this node.
     if (node->parents.size() == 0) {
diff --git a/src/mongo/db/views/view_graph.h b/src/mongo/db/views/view_graph.h
index 98fefdb91dc..2653f1b5aa1 100644
--- a/src/mongo/db/views/view_graph.h
+++ b/src/mongo/db/views/view_graph.h
@@ -105,18 +105,11 @@ private:
     // This node represents a view namespace if and only if 'children' is nonempty and 'collator' is
     // set.
     struct Node {
-        Node() = default;
-        Node(const Node& other)
-            : ns(other.ns), children(other.children), parents(other.parents), size(other.size) {
-            if (other.collator) {
-                collator = CollatorInterface::cloneCollator(other.collator.get());
-            }
-        }
-
         /**
          * Returns true if this node represents a view.
          */
         bool isView() const {
+            invariant(children.empty() == !static_cast<bool>(collator));
             return !children.empty();
         }
 
@@ -131,10 +124,10 @@ private:
         // Represents the views that depend on this namespace.
         stdx::unordered_set<uint64_t> parents;
 
-        // When set to nullptr, the view either has the binary collation or this namespace is not a
-        // view and we don't care about its collator. Verify if view with isView. ViewGraph owns the
-        // collator in order to keep pointer alive after insertion.
-        std::unique_ptr<const CollatorInterface> collator;
+        // When set, this is an unowned pointer to the view's collation, or nullptr if the view has
+        // the binary collation. When not set, this namespace is not a view and we don't care about
+        // its collator.
+        boost::optional<const CollatorInterface*> collator;
 
         // The size of this view's "pipeline", in bytes.
         int size = 0;