SERVER-42600 Implement the FCV 4.4 checkShardVersion protocol

15 files changed, 82 insertions, 52 deletions

diff --git a/src/mongo/db/commands/find_and_modify.cpp b/src/mongo/db/commands/find_and_modify.cpp
index b12ccc69717..6c8fde275fb 100644
--- a/src/mongo/db/commands/find_and_modify.cpp
+++ b/src/mongo/db/commands/find_and_modify.cpp
@@ -175,7 +175,7 @@ void appendCommandResponse(const PlanExecutor* exec,
     }
 }
 
-void assertCanWrite(OperationContext* opCtx, const NamespaceString& nsString) {
+void assertCanWrite(OperationContext* opCtx, const NamespaceString& nsString, bool isCollection) {
     uassert(ErrorCodes::NotMaster,
             str::stream() << "Not primary while running findAndModify command on collection "
                           << nsString.ns(),
@@ -183,7 +183,7 @@ void assertCanWrite(OperationContext* opCtx, const NamespaceString& nsString) {
 
     // Check for shard version match
     auto css = CollectionShardingState::get(opCtx, nsString);
-    css->checkShardVersionOrThrow(opCtx);
+    css->checkShardVersionOrThrow(opCtx, isCollection);
 }
 
 void recordStatsForTopCommand(OperationContext* opCtx) {
@@ -276,7 +276,7 @@ public:
                     autoColl.getDb());
 
             auto css = CollectionShardingState::get(opCtx, nsString);
-            css->checkShardVersionOrThrow(opCtx);
+            css->checkShardVersionOrThrow(opCtx, autoColl.getCollection());
 
             Collection* const collection = autoColl.getCollection();
             const auto exec =
@@ -301,7 +301,7 @@ public:
                     autoColl.getDb());
 
             auto css = CollectionShardingState::get(opCtx, nsString);
-            css->checkShardVersionOrThrow(opCtx);
+            css->checkShardVersionOrThrow(opCtx, autoColl.getCollection());
 
             Collection* const collection = autoColl.getCollection();
             const auto exec =
@@ -389,7 +389,7 @@ public:
                     CurOp::get(opCtx)->enter_inlock(nsString.ns().c_str(), dbProfilingLevel);
                 }
 
-                assertCanWrite(opCtx, nsString);
+                assertCanWrite(opCtx, nsString, autoColl.getCollection());
 
                 Collection* const collection = autoColl.getCollection();
                 checkIfTransactionOnCappedColl(collection, inTransaction);
@@ -455,7 +455,7 @@ public:
                     CurOp::get(opCtx)->enter_inlock(nsString.ns().c_str(), dbProfilingLevel);
                 }
 
-                assertCanWrite(opCtx, nsString);
+                assertCanWrite(opCtx, nsString, autoColl->getCollection());
 
                 Collection* collection = autoColl->getCollection();
 
@@ -472,7 +472,8 @@ public:
                     autoColl.reset();
                     autoDb.emplace(opCtx, dbName, MODE_X);
 
-                    assertCanWrite(opCtx, nsString);
+                    assertCanWrite(
+                        opCtx, nsString, autoDb->getDb()->getCollection(opCtx, nsString));
 
                     collection = autoDb->getDb()->getCollection(opCtx, nsString);
 
diff --git a/src/mongo/db/commands/mr.cpp b/src/mongo/db/commands/mr.cpp
index 805ea654158..e67f97700b9 100644
--- a/src/mongo/db/commands/mr.cpp
+++ b/src/mongo/db/commands/mr.cpp
@@ -1413,7 +1413,8 @@ bool runMapReduce(OperationContext* opCtx,
 
     const auto metadata = [&] {
         AutoGetCollectionForReadCommand autoColl(opCtx, config.nss);
-        return CollectionShardingState::get(opCtx, config.nss)->getOrphansFilter(opCtx);
+        return CollectionShardingState::get(opCtx, config.nss)
+            ->getOrphansFilter(opCtx, autoColl.getCollection());
     }();
 
     bool shouldHaveData = false;
diff --git a/src/mongo/db/db_raii.cpp b/src/mongo/db/db_raii.cpp
index c851fcfcc9c..854b02fbdf6 100644
--- a/src/mongo/db/db_raii.cpp
+++ b/src/mongo/db/db_raii.cpp
@@ -316,13 +316,13 @@ AutoGetCollectionForReadCommand::AutoGetCollectionForReadCommand(
                     _autoCollForRead.getDb() ? _autoCollForRead.getDb()->getProfilingLevel()
                                              : kDoNotChangeProfilingLevel,
                     deadline) {
-    if (!_autoCollForRead.getView()) {
-        // Perform the check early so the query planner would be able to extract the correct
-        // shard key. Also make sure that version is compatible if query planner decides to
-        // use an empty plan.
-        auto css = CollectionShardingState::get(opCtx, _autoCollForRead.getNss());
-        css->checkShardVersionOrThrow(opCtx);
-    }
+
+    // Perform the check early so the query planner would be able to extract the correct
+    // shard key. Also make sure that version is compatible if query planner decides to
+    // use an empty plan.
+    invariant(!_autoCollForRead.getView() || !_autoCollForRead.getCollection());
+    auto css = CollectionShardingState::get(opCtx, _autoCollForRead.getNss());
+    css->checkShardVersionOrThrow(opCtx, _autoCollForRead.getCollection());
 }
 
 OldClientContext::OldClientContext(OperationContext* opCtx, const std::string& ns, bool doVersion)
@@ -344,7 +344,8 @@ OldClientContext::OldClientContext(OperationContext* opCtx, const std::string& n
                 break;
             default:
                 CollectionShardingState::get(_opCtx, NamespaceString(ns))
-                    ->checkShardVersionOrThrow(_opCtx);
+                    ->checkShardVersionOrThrow(_opCtx,
+                                               _db->getCollection(opCtx, NamespaceString(ns)));
                 break;
         }
     }
diff --git a/src/mongo/db/ops/write_ops_exec.cpp b/src/mongo/db/ops/write_ops_exec.cpp
index 6dd5bca5b4c..f5b9791cf00 100644
--- a/src/mongo/db/ops/write_ops_exec.cpp
+++ b/src/mongo/db/ops/write_ops_exec.cpp
@@ -193,12 +193,12 @@ private:
     repl::OpTime _opTimeAtLastOpStart;
 };
 
-void assertCanWrite_inlock(OperationContext* opCtx, const NamespaceString& ns) {
+void assertCanWrite_inlock(OperationContext* opCtx, const NamespaceString& ns, bool isCollection) {
     uassert(ErrorCodes::PrimarySteppedDown,
             str::stream() << "Not primary while writing to " << ns.ns(),
             repl::ReplicationCoordinator::get(opCtx->getServiceContext())
                 ->canAcceptWritesFor(opCtx, ns));
-    CollectionShardingState::get(opCtx, ns)->checkShardVersionOrThrow(opCtx);
+    CollectionShardingState::get(opCtx, ns)->checkShardVersionOrThrow(opCtx, isCollection);
 }
 
 void makeCollection(OperationContext* opCtx, const NamespaceString& ns) {
@@ -213,7 +213,7 @@ void makeCollection(OperationContext* opCtx, const NamespaceString& ns) {
         AutoGetOrCreateDb db(opCtx, ns.db(), MODE_IX);
         Lock::CollectionLock collLock(opCtx, ns, MODE_X);
 
-        assertCanWrite_inlock(opCtx, ns);
+        assertCanWrite_inlock(opCtx, ns, db.getDb()->getCollection(opCtx, ns));
         if (!db.getDb()->getCollection(opCtx, ns)) {  // someone else may have beat us to it.
             uassertStatusOK(userAllowedCreateNS(ns.db(), ns.coll()));
             WriteUnitOfWork wuow(opCtx);
@@ -390,7 +390,7 @@ bool insertBatchAndHandleErrors(OperationContext* opCtx,
         }
 
         curOp.raiseDbProfileLevel(collection->getDb()->getProfilingLevel());
-        assertCanWrite_inlock(opCtx, wholeOp.getNamespace());
+        assertCanWrite_inlock(opCtx, wholeOp.getNamespace(), collection->getCollection());
 
         CurOpFailpointHelpers::waitWhileFailPointEnabled(
             &hangWithLockDuringBatchInsert, opCtx, "hangWithLockDuringBatchInsert");
@@ -635,7 +635,7 @@ static SingleWriteResult performSingleUpdateOp(OperationContext* opCtx,
         curOp.raiseDbProfileLevel(collection->getDb()->getProfilingLevel());
     }
 
-    assertCanWrite_inlock(opCtx, ns);
+    assertCanWrite_inlock(opCtx, ns, collection->getCollection());
 
     auto exec = uassertStatusOK(
         getExecutorUpdate(opCtx, &curOp.debug(), collection->getCollection(), &parsedUpdate));
@@ -871,7 +871,7 @@ static SingleWriteResult performSingleDeleteOp(OperationContext* opCtx,
         curOp.raiseDbProfileLevel(collection.getDb()->getProfilingLevel());
     }
 
-    assertCanWrite_inlock(opCtx, ns);
+    assertCanWrite_inlock(opCtx, ns, collection.getCollection());
 
     CurOpFailpointHelpers::waitWhileFailPointEnabled(
         &hangWithLockDuringBatchRemove, opCtx, "hangWithLockDuringBatchRemove");
diff --git a/src/mongo/db/pipeline/pipeline_d.cpp b/src/mongo/db/pipeline/pipeline_d.cpp
index 3efb9b5813f..bd7a5cf7739 100644
--- a/src/mongo/db/pipeline/pipeline_d.cpp
+++ b/src/mongo/db/pipeline/pipeline_d.cpp
@@ -127,7 +127,8 @@ StatusWith<unique_ptr<PlanExecutor, PlanExecutor::Deleter>> createRandomCursorEx
 
     // If the incoming operation is sharded, use the CSS to infer the filtering metadata for the
     // collection, otherwise treat it as unsharded
-    auto shardMetadata = CollectionShardingState::get(opCtx, coll->ns())->getOrphansFilter(opCtx);
+    auto shardMetadata =
+        CollectionShardingState::get(opCtx, coll->ns())->getOrphansFilter(opCtx, coll);
 
     // Because 'numRecords' includes orphan documents, our initial decision to optimize the $sample
     // cursor may have been mistaken. For sharded collections, build a TRIAL plan that will switch
diff --git a/src/mongo/db/pipeline/process_interface_shardsvr.cpp b/src/mongo/db/pipeline/process_interface_shardsvr.cpp
index 74508c4a10e..b9b69d4e9d9 100644
--- a/src/mongo/db/pipeline/process_interface_shardsvr.cpp
+++ b/src/mongo/db/pipeline/process_interface_shardsvr.cpp
@@ -206,8 +206,9 @@ unique_ptr<Pipeline, PipelineDeleter> MongoInterfaceShardServer::attachCursorSou
 
 std::unique_ptr<ShardFilterer> MongoInterfaceShardServer::getShardFilterer(
     const boost::intrusive_ptr<ExpressionContext>& expCtx) const {
-    auto shardingMetadata =
-        CollectionShardingState::get(expCtx->opCtx, expCtx->ns)->getOrphansFilter(expCtx->opCtx);
+    const bool aggNsIsCollection = expCtx->uuid != boost::none;
+    auto shardingMetadata = CollectionShardingState::get(expCtx->opCtx, expCtx->ns)
+                                ->getOrphansFilter(expCtx->opCtx, aggNsIsCollection);
     return std::make_unique<ShardFiltererImpl>(std::move(shardingMetadata));
 }
 
diff --git a/src/mongo/db/query/get_executor.cpp b/src/mongo/db/query/get_executor.cpp
index 7e8c0d1e9b4..804baeb123d 100644
--- a/src/mongo/db/query/get_executor.cpp
+++ b/src/mongo/db/query/get_executor.cpp
@@ -382,7 +382,8 @@ StatusWith<PrepareExecutionResult> prepareExecution(OperationContext* opCtx,
         if (plannerParams.options & QueryPlannerParams::INCLUDE_SHARD_FILTER) {
             root = std::make_unique<ShardFilterStage>(
                 opCtx,
-                CollectionShardingState::get(opCtx, canonicalQuery->nss())->getOrphansFilter(opCtx),
+                CollectionShardingState::get(opCtx, canonicalQuery->nss())
+                    ->getOrphansFilter(opCtx, collection),
                 ws,
                 root.release());
         }
diff --git a/src/mongo/db/query/stage_builder.cpp b/src/mongo/db/query/stage_builder.cpp
index 382e3652354..508690ae278 100644
--- a/src/mongo/db/query/stage_builder.cpp
+++ b/src/mongo/db/query/stage_builder.cpp
@@ -312,7 +312,8 @@ PlanStage* buildStages(OperationContext* opCtx,
             }
 
             auto css = CollectionShardingState::get(opCtx, collection->ns());
-            return new ShardFilterStage(opCtx, css->getOrphansFilter(opCtx), ws, childStage);
+            return new ShardFilterStage(
+                opCtx, css->getOrphansFilter(opCtx, collection), ws, childStage);
         }
         case STAGE_DISTINCT_SCAN: {
             const DistinctNode* dn = static_cast<const DistinctNode*>(root);
diff --git a/src/mongo/db/s/collection_metadata_filtering_test.cpp b/src/mongo/db/s/collection_metadata_filtering_test.cpp
index 34ff588020f..da000652d40 100644
--- a/src/mongo/db/s/collection_metadata_filtering_test.cpp
+++ b/src/mongo/db/s/collection_metadata_filtering_test.cpp
@@ -139,7 +139,7 @@ TEST_F(CollectionMetadataFilteringTest, FilterDocumentsInTheFuture) {
 
         AutoGetCollection autoColl(operationContext(), kNss, MODE_IS);
         auto* const css = CollectionShardingState::get(operationContext(), kNss);
-        testFn(css->getOrphansFilter(operationContext()));
+        testFn(css->getOrphansFilter(operationContext(), true /* isCollection */));
     }
 
     {
@@ -169,7 +169,7 @@ TEST_F(CollectionMetadataFilteringTest, FilterDocumentsInThePast) {
 
         AutoGetCollection autoColl(operationContext(), kNss, MODE_IS);
         auto* const css = CollectionShardingState::get(operationContext(), kNss);
-        testFn(css->getOrphansFilter(operationContext()));
+        testFn(css->getOrphansFilter(operationContext(), true /* isCollection */));
     }
 
     {
@@ -207,7 +207,7 @@ TEST_F(CollectionMetadataFilteringTest, FilterDocumentsTooFarInThePastThrowsStal
 
         AutoGetCollection autoColl(operationContext(), kNss, MODE_IS);
         auto* const css = CollectionShardingState::get(operationContext(), kNss);
-        testFn(css->getOrphansFilter(operationContext()));
+        testFn(css->getOrphansFilter(operationContext(), true /* isCollection */));
     }
 
     {
diff --git a/src/mongo/db/s/collection_sharding_state.cpp b/src/mongo/db/s/collection_sharding_state.cpp
index feb519090e3..02b5406f625 100644
--- a/src/mongo/db/s/collection_sharding_state.cpp
+++ b/src/mongo/db/s/collection_sharding_state.cpp
@@ -37,10 +37,14 @@
 #include "mongo/db/s/operation_sharding_state.h"
 #include "mongo/db/s/sharded_connection_info.h"
 #include "mongo/s/stale_exception.h"
+#include "mongo/util/fail_point_service.h"
 #include "mongo/util/log.h"
 #include "mongo/util/string_map.h"
 
 namespace mongo {
+
+MONGO_FAIL_POINT_DEFINE(useFCV44CheckShardVersionProtocol);
+
 namespace {
 
 class CollectionShardingStateMap {
@@ -159,9 +163,10 @@ void CollectionShardingState::report(OperationContext* opCtx, BSONObjBuilder* bu
     collectionsMap->report(opCtx, builder);
 }
 
-ScopedCollectionMetadata CollectionShardingState::getOrphansFilter(OperationContext* opCtx) {
+ScopedCollectionMetadata CollectionShardingState::getOrphansFilter(OperationContext* opCtx,
+                                                                   bool isCollection) {
     const auto atClusterTime = repl::ReadConcernArgs::get(opCtx).getArgsAtClusterTime();
-    auto optMetadata = _getMetadataWithVersionCheckAt(opCtx, atClusterTime);
+    auto optMetadata = _getMetadataWithVersionCheckAt(opCtx, atClusterTime, isCollection);
 
     if (!optMetadata)
         return {kUnshardedCollection};
@@ -194,12 +199,14 @@ boost::optional<ChunkVersion> CollectionShardingState::getCurrentShardVersionIfK
     return metadata->getCollVersion();
 }
 
-void CollectionShardingState::checkShardVersionOrThrow(OperationContext* opCtx) {
-    (void)_getMetadataWithVersionCheckAt(opCtx, boost::none);
+void CollectionShardingState::checkShardVersionOrThrow(OperationContext* opCtx, bool isCollection) {
+    (void)_getMetadataWithVersionCheckAt(opCtx, boost::none, isCollection);
 }
 
 boost::optional<ScopedCollectionMetadata> CollectionShardingState::_getMetadataWithVersionCheckAt(
-    OperationContext* opCtx, const boost::optional<mongo::LogicalTime>& atClusterTime) {
+    OperationContext* opCtx,
+    const boost::optional<mongo::LogicalTime>& atClusterTime,
+    bool isCollection) {
     const auto optReceivedShardVersion = getOperationReceivedVersion(opCtx, _nss);
 
     if (!optReceivedShardVersion)
@@ -218,8 +225,22 @@ boost::optional<ScopedCollectionMetadata> CollectionShardingState::_getMetadataW
 
     auto metadata = _getMetadata(atClusterTime);
     auto wantedShardVersion = ChunkVersion::UNSHARDED();
-    if (metadata && (*metadata)->isSharded()) {
-        wantedShardVersion = (*metadata)->getShardVersion();
+
+    if (MONGO_FAIL_POINT(useFCV44CheckShardVersionProtocol)) {
+        LOG(0) << "Received shardVersion: " << receivedShardVersion << " for " << _nss.ns();
+        if (isCollection) {
+            LOG(0) << "Namespace " << _nss.ns() << " is collection, "
+                   << (metadata ? "have shardVersion cached" : "don't know shardVersion");
+            uassert(StaleConfigInfo(_nss, receivedShardVersion, wantedShardVersion),
+                    "don't know shardVersion",
+                    metadata);
+            wantedShardVersion = (*metadata)->getShardVersion();
+        }
+        LOG(0) << "Wanted shardVersion: " << wantedShardVersion << " for " << _nss.ns();
+    } else {
+        if (metadata && (*metadata)->isSharded()) {
+            wantedShardVersion = (*metadata)->getShardVersion();
+        }
     }
 
     auto criticalSectionSignal = [&] {
diff --git a/src/mongo/db/s/collection_sharding_state.h b/src/mongo/db/s/collection_sharding_state.h
index 906c366b8fb..cc246dacdab 100644
--- a/src/mongo/db/s/collection_sharding_state.h
+++ b/src/mongo/db/s/collection_sharding_state.h
@@ -97,7 +97,7 @@ public:
      *
      * The returned object is safe to access even after the collection lock has been dropped.
      */
-    ScopedCollectionMetadata getOrphansFilter(OperationContext* opCtx);
+    ScopedCollectionMetadata getOrphansFilter(OperationContext* opCtx, bool isCollection);
 
     /**
      * See the comments for 'getOrphansFilter' above for more information on this method.
@@ -120,7 +120,7 @@ public:
      * version of the collection and if not, throws StaleConfigException populated with the received
      * and wanted versions.
      */
-    void checkShardVersionOrThrow(OperationContext* opCtx);
+    void checkShardVersionOrThrow(OperationContext* opCtx, bool isCollection);
 
     /**
      * Methods to control the collection's critical section. Methods listed below must be called
@@ -161,7 +161,9 @@ private:
      * atClusterTime if specified.
      */
     boost::optional<ScopedCollectionMetadata> _getMetadataWithVersionCheckAt(
-        OperationContext* opCtx, const boost::optional<mongo::LogicalTime>& atClusterTime);
+        OperationContext* opCtx,
+        const boost::optional<mongo::LogicalTime>& atClusterTime,
+        bool isCollection);
 
     // Object-wide ResourceMutex to protect changes to the CollectionShardingRuntime or objects
     // held within. Use only the CollectionShardingRuntimeLock to lock this mutex.
diff --git a/src/mongo/db/s/get_shard_version_command.cpp b/src/mongo/db/s/get_shard_version_command.cpp
index 87ea9653eb1..4dcc90be124 100644
--- a/src/mongo/db/s/get_shard_version_command.cpp
+++ b/src/mongo/db/s/get_shard_version_command.cpp
@@ -106,7 +106,8 @@ public:
             result.appendTimestamp("mine", 0);
         }
 
-        AutoGetCollection autoColl(opCtx, nss, MODE_IS);
+        AutoGetCollection autoColl(
+            opCtx, nss, MODE_IS, AutoGetCollection::ViewMode::kViewsPermitted);
         auto* const css = CollectionShardingRuntime::get(opCtx, nss);
 
         const auto optMetadata = css->getCurrentMetadataIfKnown();
diff --git a/src/mongo/db/s/op_observer_sharding_impl.cpp b/src/mongo/db/s/op_observer_sharding_impl.cpp
index 606d8ae7dfc..a76bbd1bcb2 100644
--- a/src/mongo/db/s/op_observer_sharding_impl.cpp
+++ b/src/mongo/db/s/op_observer_sharding_impl.cpp
@@ -55,7 +55,7 @@ void assertIntersectingChunkHasNotMoved(OperationContext* opCtx,
     if (!repl::ReadConcernArgs::get(opCtx).getArgsAtClusterTime())
         return;
 
-    const auto metadata = csr->getOrphansFilter(opCtx);
+    const auto metadata = csr->getOrphansFilter(opCtx, true /* isCollection */);
     if (!metadata->isSharded())
         return;
 
@@ -105,7 +105,7 @@ void OpObserverShardingImpl::shardObserveInsertOp(OperationContext* opCtx,
         return;
     }
 
-    csr->checkShardVersionOrThrow(opCtx);
+    csr->checkShardVersionOrThrow(opCtx, true /* isCollection */);
 
     if (inMultiDocumentTransaction) {
         assertIntersectingChunkHasNotMoved(opCtx, csr, insertedDoc);
@@ -127,7 +127,7 @@ void OpObserverShardingImpl::shardObserveUpdateOp(OperationContext* opCtx,
                                                   const repl::OpTime& prePostImageOpTime,
                                                   const bool inMultiDocumentTransaction) {
     auto* const csr = CollectionShardingRuntime::get(opCtx, nss);
-    csr->checkShardVersionOrThrow(opCtx);
+    csr->checkShardVersionOrThrow(opCtx, true /* isCollection */);
 
     if (inMultiDocumentTransaction) {
         assertIntersectingChunkHasNotMoved(opCtx, csr, postImageDoc);
@@ -148,7 +148,7 @@ void OpObserverShardingImpl::shardObserveDeleteOp(OperationContext* opCtx,
                                                   const repl::OpTime& preImageOpTime,
                                                   const bool inMultiDocumentTransaction) {
     auto* const csr = CollectionShardingRuntime::get(opCtx, nss);
-    csr->checkShardVersionOrThrow(opCtx);
+    csr->checkShardVersionOrThrow(opCtx, true /* isCollection */);
 
     if (inMultiDocumentTransaction) {
         assertIntersectingChunkHasNotMoved(opCtx, csr, documentKey);
diff --git a/src/mongo/db/s/operation_sharding_state.cpp b/src/mongo/db/s/operation_sharding_state.cpp
index 3284b5e825c..0a726714fd6 100644
--- a/src/mongo/db/s/operation_sharding_state.cpp
+++ b/src/mongo/db/s/operation_sharding_state.cpp
@@ -110,7 +110,8 @@ bool OperationShardingState::hasShardVersion() const {
     return _globalUnshardedShardVersion || !_shardVersions.empty();
 }
 
-ChunkVersion OperationShardingState::getShardVersion(const NamespaceString& nss) const {
+boost::optional<ChunkVersion> OperationShardingState::getShardVersion(
+    const NamespaceString& nss) const {
     if (_globalUnshardedShardVersion) {
         return ChunkVersion::UNSHARDED();
     }
@@ -119,9 +120,8 @@ ChunkVersion OperationShardingState::getShardVersion(const NamespaceString& nss)
     if (it != _shardVersions.end()) {
         return it->second;
     }
-    // If the client did not send a shardVersion for the requested namespace, assume the client
-    // expected the namespace to be unsharded.
-    return ChunkVersion::UNSHARDED();
+
+    return boost::none;
 }
 
 bool OperationShardingState::hasDbVersion() const {
diff --git a/src/mongo/db/s/operation_sharding_state.h b/src/mongo/db/s/operation_sharding_state.h
index c24b451e274..d99227e0254 100644
--- a/src/mongo/db/s/operation_sharding_state.h
+++ b/src/mongo/db/s/operation_sharding_state.h
@@ -108,10 +108,9 @@ public:
      * operation. Documents in chunks which did not belong on this shard at this shard version
      * will be filtered out.
      *
-     * Returns ChunkVersion::UNSHARDED() if this operation has no shard version information
-     * for the requested namespace.
+     * Returns ChunkVersion::UNSHARDED() if setGlobalUnshardedShardVersion has been called.
      */
-    ChunkVersion getShardVersion(const NamespaceString& nss) const;
+    boost::optional<ChunkVersion> getShardVersion(const NamespaceString& nss) const;
 
     /**
      * Returns true if the client sent a databaseVersion for any namespace.