SERVER-32597 Bump generic fCV references

20 files changed, 60 insertions, 73 deletions

diff --git a/src/mongo/db/catalog/coll_mod.cpp b/src/mongo/db/catalog/coll_mod.cpp
index 5775c04d4e1..4ef185fde2c 100644
--- a/src/mongo/db/catalog/coll_mod.cpp
+++ b/src/mongo/db/catalog/coll_mod.cpp
@@ -416,7 +416,7 @@ Status _collModInternal(OperationContext* opCtx,
             cce->addUUID(opCtx, uuid.get(), coll);
         } else if (!uuid && coll->uuid() &&
                    serverGlobalParams.featureCompatibility.getVersion() <
-                       ServerGlobalParams::FeatureCompatibility::Version::kFullyUpgradedTo36) {
+                       ServerGlobalParams::FeatureCompatibility::Version::kFullyDowngradedTo36) {
             log() << "Removing UUID " << coll->uuid().get().toString() << " from collection "
                   << coll->ns();
             CollectionCatalogEntry* cce = coll->getCatalogEntry();
diff --git a/src/mongo/db/catalog/database_impl.cpp b/src/mongo/db/catalog/database_impl.cpp
index d81fcef249e..7206621a5f5 100644
--- a/src/mongo/db/catalog/database_impl.cpp
+++ b/src/mongo/db/catalog/database_impl.cpp
@@ -772,16 +772,13 @@ Collection* DatabaseImpl::createCollection(OperationContext* opCtx,
 
     CollectionOptions optionsWithUUID = options;
     bool generatedUUID = false;
-    if (enableCollectionUUIDs && !optionsWithUUID.uuid &&
-        serverGlobalParams.featureCompatibility.isSchemaVersion36()) {
+    if (!optionsWithUUID.uuid) {
         auto coordinator = repl::ReplicationCoordinator::get(opCtx);
-        bool fullyUpgraded = serverGlobalParams.featureCompatibility.getVersion() >=
-            ServerGlobalParams::FeatureCompatibility::Version::kFullyUpgradedTo36;
         bool canGenerateUUID =
             (coordinator->getReplicationMode() != repl::ReplicationCoordinator::modeReplSet) ||
             coordinator->canAcceptWritesForDatabase(opCtx, nss.db()) || nss.isSystemDotProfile();
 
-        if (fullyUpgraded && !canGenerateUUID) {
+        if (!canGenerateUUID) {
             std::string msg = str::stream() << "Attempted to create a new collection " << nss.ns()
                                             << " without a UUID";
             severe() << msg;
diff --git a/src/mongo/db/catalog/index_spec_validate_test.cpp b/src/mongo/db/catalog/index_spec_validate_test.cpp
index 471f1a525ca..9af8fa54b01 100644
--- a/src/mongo/db/catalog/index_spec_validate_test.cpp
+++ b/src/mongo/db/catalog/index_spec_validate_test.cpp
@@ -401,7 +401,7 @@ TEST(IndexSpecValidateTest, AcceptsIndexVersionV1) {
 TEST(IndexSpecValidateTest, AcceptsIndexVersionV2Unique) {
     ServerGlobalParams::FeatureCompatibility featureCompatibility;
     featureCompatibility.setVersion(
-        ServerGlobalParams::FeatureCompatibility::Version::kFullyUpgradedTo36);
+        ServerGlobalParams::FeatureCompatibility::Version::kFullyUpgradedTo40);
 
     auto result = validateIndexSpec(kDefaultOpCtx,
                                     BSON("key" << BSON("field" << 1) << "name"
@@ -420,6 +420,7 @@ TEST(IndexSpecValidateTest, AcceptsIndexVersionV2Unique) {
                                         << "v"
                                         << 3)),
                       sorted(result.getValue()));
+    featureCompatibility.reset();
 }
 TEST(IndexSpecValidateTest, ReturnsAnErrorIfCollationIsNotAnObject) {
     ASSERT_EQ(ErrorCodes::TypeMismatch,
diff --git a/src/mongo/db/commands/dbcheck.cpp b/src/mongo/db/commands/dbcheck.cpp
index 08b062718d7..d0c1ee0673e 100644
--- a/src/mongo/db/commands/dbcheck.cpp
+++ b/src/mongo/db/commands/dbcheck.cpp
@@ -534,8 +534,6 @@ public:
                      const std::string& dbname,
                      const BSONObj& cmdObj,
                      BSONObjBuilder& result) {
-        uassert(40614, "dbCheck requires FeatureCompatibilityVersion >= 3.6", _hasCorrectFCV());
-
         auto job = getRun(opCtx, dbname, cmdObj);
         try {
             (new DbCheckJob(dbname, std::move(job)))->go();
@@ -547,12 +545,6 @@ public:
         result.append("ok", true);
         return true;
     }
-
-private:
-    bool _hasCorrectFCV(void) {
-        return serverGlobalParams.featureCompatibility.getVersion() >=
-            ServerGlobalParams::FeatureCompatibility::Version::kFullyUpgradedTo36;
-    }
 };
 
 MONGO_INITIALIZER(RegisterDbCheckCmd)(InitializerContext* context) {
diff --git a/src/mongo/db/commands/feature_compatibility_version.cpp b/src/mongo/db/commands/feature_compatibility_version.cpp
index e8147b511fc..60014e63785 100644
--- a/src/mongo/db/commands/feature_compatibility_version.cpp
+++ b/src/mongo/db/commands/feature_compatibility_version.cpp
@@ -166,7 +166,7 @@ StatusWith<ServerGlobalParams::FeatureCompatibility::Version> FeatureCompatibili
                                         << feature_compatibility_version::kDochubLink
                                         << ".");
         } else {
-            version = ServerGlobalParams::FeatureCompatibility::Version::kFullyUpgradedTo36;
+            version = ServerGlobalParams::FeatureCompatibility::Version::kFullyDowngradedTo36;
         }
     } else if (versionString == FeatureCompatibilityVersionCommandParser::kVersion40) {
         if (targetVersionString == FeatureCompatibilityVersionCommandParser::kVersion40 ||
@@ -276,7 +276,6 @@ void FeatureCompatibilityVersion::setIfCleanStartup(OperationContext* opCtx,
 
     // We then insert the featureCompatibilityVersion document into the "admin.system.version"
     // collection. The server parameter will be updated on commit by the op observer.
-    // TODO(SERVER-32597): If storeUpgradeVersion is true, kVersion38 should be stored.
     uassertStatusOK(storageInterface->insertDocument(
         opCtx,
         nss,
@@ -284,7 +283,7 @@ void FeatureCompatibilityVersion::setIfCleanStartup(OperationContext* opCtx,
             BSON("_id" << FeatureCompatibilityVersion::kParameterName
                        << FeatureCompatibilityVersion::kVersionField
                        << (storeUpgradeVersion
-                               ? FeatureCompatibilityVersionCommandParser::kVersion36
+                               ? FeatureCompatibilityVersionCommandParser::kVersion40
                                : FeatureCompatibilityVersionCommandParser::kVersion36)),
             Timestamp()},
         repl::OpTime::kUninitializedTerm));  // No timestamp or term because this write is not
@@ -328,7 +327,7 @@ void FeatureCompatibilityVersion::onInsertOrUpdate(OperationContext* opCtx, cons
         // Close all incoming connections from internal clients with binary versions lower than
         // ours. It would be desirable to close all outgoing connections to servers with lower
         // binary version, but it is not currently possible.
-        if (newVersion != ServerGlobalParams::FeatureCompatibility::Version::kFullyDowngradedTo34) {
+        if (newVersion != ServerGlobalParams::FeatureCompatibility::Version::kFullyDowngradedTo36) {
             opCtx->getServiceContext()->getServiceEntryPoint()->endAllSessions(
                 transport::Session::kLatestVersionInternalClientKeepOpen |
                 transport::Session::kExternalClientKeepOpen);
@@ -357,7 +356,7 @@ void FeatureCompatibilityVersion::onDropCollection(OperationContext* opCtx) {
           << FeatureCompatibilityVersionCommandParser::kVersion36;
     opCtx->recoveryUnit()->onCommit([]() {
         serverGlobalParams.featureCompatibility.setVersion(
-            ServerGlobalParams::FeatureCompatibility::Version::kFullyUpgradedTo36);
+            ServerGlobalParams::FeatureCompatibility::Version::kFullyDowngradedTo36);
         updateMinWireVersion();
     });
 }
@@ -372,7 +371,7 @@ void FeatureCompatibilityVersion::updateMinWireVersion() {
             spec.incomingInternalClient.minWireVersion = LATEST_WIRE_VERSION;
             spec.outgoing.minWireVersion = LATEST_WIRE_VERSION;
             return;
-        case ServerGlobalParams::FeatureCompatibility::Version::kFullyUpgradedTo36:
+        case ServerGlobalParams::FeatureCompatibility::Version::kFullyDowngradedTo36:
         case ServerGlobalParams::FeatureCompatibility::Version::kUpgradingTo36:
         case ServerGlobalParams::FeatureCompatibility::Version::kDowngradingTo34:
             spec.incomingInternalClient.minWireVersion = LATEST_WIRE_VERSION - 1;
@@ -471,7 +470,7 @@ public:
                     FeatureCompatibilityVersion::kTargetVersionField,
                     FeatureCompatibilityVersionCommandParser::kVersion36);
                 return;
-            case ServerGlobalParams::FeatureCompatibility::Version::kFullyUpgradedTo36:
+            case ServerGlobalParams::FeatureCompatibility::Version::kFullyDowngradedTo36:
                 featureCompatibilityVersionBuilder.append(
                     FeatureCompatibilityVersion::kVersionField,
                     FeatureCompatibilityVersionCommandParser::kVersion36);
diff --git a/src/mongo/db/commands/feature_compatibility_version.h b/src/mongo/db/commands/feature_compatibility_version.h
index 45a020c4762..aab764f7ea9 100644
--- a/src/mongo/db/commands/feature_compatibility_version.h
+++ b/src/mongo/db/commands/feature_compatibility_version.h
@@ -81,7 +81,7 @@ public:
                 return FeatureCompatibilityVersionCommandParser::kVersionUpgradingTo36;
             case ServerGlobalParams::FeatureCompatibility::Version::kDowngradingTo34:
                 return FeatureCompatibilityVersionCommandParser::kVersionDowngradingTo34;
-            case ServerGlobalParams::FeatureCompatibility::Version::kFullyUpgradedTo36:
+            case ServerGlobalParams::FeatureCompatibility::Version::kFullyDowngradedTo36:
                 return FeatureCompatibilityVersionCommandParser::kVersion36;
             case ServerGlobalParams::FeatureCompatibility::Version::kUpgradingTo40:
                 return FeatureCompatibilityVersionCommandParser::kVersionUpgradingTo40;
diff --git a/src/mongo/db/commands/feature_compatibility_version_command_parser.h b/src/mongo/db/commands/feature_compatibility_version_command_parser.h
index 9097f16385e..0f19576765e 100644
--- a/src/mongo/db/commands/feature_compatibility_version_command_parser.h
+++ b/src/mongo/db/commands/feature_compatibility_version_command_parser.h
@@ -39,7 +39,7 @@ template <typename T>
 class StatusWith;
 
 namespace feature_compatibility_version {
-constexpr StringData kDochubLink = "http://dochub.mongodb.org/core/3.6-feature-compatibility"_sd;
+constexpr StringData kDochubLink = "http://dochub.mongodb.org/core/4.0-feature-compatibility"_sd;
 }  // namespace feature_compatibility_version
 
 class FeatureCompatibilityVersionCommandParser {
diff --git a/src/mongo/db/commands/set_feature_compatibility_version_command.cpp b/src/mongo/db/commands/set_feature_compatibility_version_command.cpp
index ca26df5dcff..e9b510d4120 100644
--- a/src/mongo/db/commands/set_feature_compatibility_version_command.cpp
+++ b/src/mongo/db/commands/set_feature_compatibility_version_command.cpp
@@ -198,7 +198,7 @@ public:
                         ServerGlobalParams::FeatureCompatibility::Version::kUpgradingTo40);
 
             if (actualVersion ==
-                ServerGlobalParams::FeatureCompatibility::Version::kFullyUpgradedTo36) {
+                ServerGlobalParams::FeatureCompatibility::Version::kFullyDowngradedTo36) {
                 // Set the client's last opTime to the system last opTime so no-ops wait for
                 // writeConcern.
                 repl::ReplClientInfo::forClient(opCtx->getClient())
diff --git a/src/mongo/db/commands/validate.cpp b/src/mongo/db/commands/validate.cpp
index 7e021018029..eb7a3175ee9 100644
--- a/src/mongo/db/commands/validate.cpp
+++ b/src/mongo/db/commands/validate.cpp
@@ -210,7 +210,8 @@ public:
             ServerGlobalParams::FeatureCompatibility::Version version =
                 serverGlobalParams.featureCompatibility.getVersion();
 
-            if (version >= ServerGlobalParams::FeatureCompatibility::Version::kFullyUpgradedTo36) {
+            if (version >=
+                ServerGlobalParams::FeatureCompatibility::Version::kFullyDowngradedTo36) {
                 // All collections must have a UUID.
                 if (!opts.uuid) {
                     results.errors.push_back(str::stream() << "UUID missing on collection "
@@ -218,15 +219,6 @@ public:
                                                            << " but SchemaVersion=3.6");
                     results.valid = false;
                 }
-            } else if (version ==
-                       ServerGlobalParams::FeatureCompatibility::Version::kFullyDowngradedTo34) {
-                // All collections must not have a UUID.
-                if (opts.uuid) {
-                    results.errors.push_back(str::stream() << "UUID present in collection "
-                                                           << nss.ns()
-                                                           << " but SchemaVersion=3.4");
-                    results.valid = false;
-                }
             }
         }
 
diff --git a/src/mongo/db/db.cpp b/src/mongo/db/db.cpp
index e50cf0ecfc8..24a7ef71828 100644
--- a/src/mongo/db/db.cpp
+++ b/src/mongo/db/db.cpp
@@ -830,11 +830,9 @@ void shutdownTask() {
             opCtx = uniqueOpCtx.get();
         }
 
-        // TODO: Upgrade this check so that this block only runs when (FCV != kFullyUpgradedTo38).
-        // See SERVER-32589.
         if (serverGlobalParams.featureCompatibility.getVersion() !=
-            ServerGlobalParams::FeatureCompatibility::Version::kFullyUpgradedTo36) {
-            // If we are in fCV 3.6, drop the 'checkpointTimestamp' collection so if we downgrade
+            ServerGlobalParams::FeatureCompatibility::Version::kFullyUpgradedTo40) {
+            // If we are in latest fCV, drop the 'checkpointTimestamp' collection so if we downgrade
             // and then upgrade again, we do not trust a stale 'checkpointTimestamp'.
             log(LogComponent::kReplication)
                 << "shutdown: removing checkpointTimestamp collection...";
diff --git a/src/mongo/db/repl/idempotency_test.cpp b/src/mongo/db/repl/idempotency_test.cpp
index 56866630784..a1e2eb215c2 100644
--- a/src/mongo/db/repl/idempotency_test.cpp
+++ b/src/mongo/db/repl/idempotency_test.cpp
@@ -192,9 +192,7 @@ void RandomizedIdempotencyTest::runIdempotencyTestCase() {
     }
 }
 
-TEST_F(RandomizedIdempotencyTest, CheckUpdateSequencesAreIdempotentWhenFCV36) {
-    serverGlobalParams.featureCompatibility.setVersion(
-        ServerGlobalParams::FeatureCompatibility::Version::kFullyUpgradedTo36);
+TEST_F(RandomizedIdempotencyTest, CheckUpdateSequencesAreIdempotent) {
     runIdempotencyTestCase();
 }
 
diff --git a/src/mongo/db/repl/initial_syncer.cpp b/src/mongo/db/repl/initial_syncer.cpp
index ed6a2086060..5e5cb8635c7 100644
--- a/src/mongo/db/repl/initial_syncer.cpp
+++ b/src/mongo/db/repl/initial_syncer.cpp
@@ -680,8 +680,10 @@ void InitialSyncer::_fcvFetcherCallback(const StatusWith<Fetcher::QueryResponse>
     }
 
     auto version = fCVParseSW.getValue();
-    if (version > ServerGlobalParams::FeatureCompatibility::Version::kFullyDowngradedTo34 &&
-        version < ServerGlobalParams::FeatureCompatibility::Version::kFullyUpgradedTo36) {
+
+    // Changing the featureCompatibilityVersion during initial sync is unsafe.
+    if (version > ServerGlobalParams::FeatureCompatibility::Version::kFullyDowngradedTo36 &&
+        version < ServerGlobalParams::FeatureCompatibility::Version::kFullyUpgradedTo40) {
         onCompletionGuard->setResultAndCancelRemainingWork_inlock(
             lock,
             Status(ErrorCodes::IncompatibleServerVersion,
diff --git a/src/mongo/db/repl/initial_syncer_test.cpp b/src/mongo/db/repl/initial_syncer_test.cpp
index 2d959fb8a5c..91d79e87e72 100644
--- a/src/mongo/db/repl/initial_syncer_test.cpp
+++ b/src/mongo/db/repl/initial_syncer_test.cpp
@@ -1542,24 +1542,24 @@ TEST_F(InitialSyncerTest,
 TEST_F(InitialSyncerTest,
        InitialSyncerReturnsIncompatibleServerVersionWhenFCVFetcherReturnsUpgradeTargetVersion) {
     auto docs = {BSON("_id" << FeatureCompatibilityVersion::kParameterName << "version"
-                            << FeatureCompatibilityVersionCommandParser::kVersion34
+                            << FeatureCompatibilityVersionCommandParser::kVersion36
                             << "targetVersion"
-                            << FeatureCompatibilityVersionCommandParser::kVersion36)};
+                            << FeatureCompatibilityVersionCommandParser::kVersion40)};
     runInitialSyncWithBadFCVResponse(docs, ErrorCodes::IncompatibleServerVersion);
 }
 
 TEST_F(InitialSyncerTest,
        InitialSyncerReturnsIncompatibleServerVersionWhenFCVFetcherReturnsDowngradeTargetVersion) {
     auto docs = {BSON("_id" << FeatureCompatibilityVersion::kParameterName << "version"
-                            << FeatureCompatibilityVersionCommandParser::kVersion34
+                            << FeatureCompatibilityVersionCommandParser::kVersion36
                             << "targetVersion"
-                            << FeatureCompatibilityVersionCommandParser::kVersion34)};
+                            << FeatureCompatibilityVersionCommandParser::kVersion36)};
     runInitialSyncWithBadFCVResponse(docs, ErrorCodes::IncompatibleServerVersion);
 }
 
 TEST_F(InitialSyncerTest, InitialSyncerReturnsBadValueWhenFCVFetcherReturnsNoVersion) {
     auto docs = {BSON("_id" << FeatureCompatibilityVersion::kParameterName << "targetVersion"
-                            << FeatureCompatibilityVersionCommandParser::kVersion34)};
+                            << FeatureCompatibilityVersionCommandParser::kVersion36)};
     runInitialSyncWithBadFCVResponse(docs, ErrorCodes::BadValue);
 }
 
@@ -1582,7 +1582,7 @@ TEST_F(InitialSyncerTest, InitialSyncerSucceedsWhenFCVFetcherReturnsOldVersion)
         processSuccessfulLastOplogEntryFetcherResponse({makeOplogEntryObj(1)});
 
         auto docs = {BSON("_id" << FeatureCompatibilityVersion::kParameterName << "version"
-                                << FeatureCompatibilityVersionCommandParser::kVersion34)};
+                                << FeatureCompatibilityVersionCommandParser::kVersion36)};
         processSuccessfulFCVFetcherResponse(docs);
         ASSERT_TRUE(net->hasReadyRequests());
     }
diff --git a/src/mongo/db/repl/sync_tail_test_fixture.cpp b/src/mongo/db/repl/sync_tail_test_fixture.cpp
index 4953a93ec41..3109ff4da05 100644
--- a/src/mongo/db/repl/sync_tail_test_fixture.cpp
+++ b/src/mongo/db/repl/sync_tail_test_fixture.cpp
@@ -94,8 +94,11 @@ void SyncTailTest::setUp() {
                    OplogApplication::Mode oplogApplicationMode) { return Status::OK(); };
     _incOps = [this]() { _opsApplied++; };
 
+    // Initialize the featureCompatibilityVersion server parameter. This is necessary because this
+    // test fixture does not create a featureCompatibilityVersion document from which to initialize
+    // the server parameter.
     serverGlobalParams.featureCompatibility.setVersion(
-        ServerGlobalParams::FeatureCompatibility::Version::kFullyUpgradedTo36);
+        ServerGlobalParams::FeatureCompatibility::Version::kFullyUpgradedTo40);
 }
 
 void SyncTailTest::tearDown() {
diff --git a/src/mongo/db/s/config/sharding_catalog_manager_shard_operations.cpp b/src/mongo/db/s/config/sharding_catalog_manager_shard_operations.cpp
index 7988dd87cdc..ec37ae9e83e 100644
--- a/src/mongo/db/s/config/sharding_catalog_manager_shard_operations.cpp
+++ b/src/mongo/db/s/config/sharding_catalog_manager_shard_operations.cpp
@@ -339,13 +339,13 @@ StatusWith<ShardType> ShardingCatalogManager::_validateHostAsShard(
                                                 << " as a shard");
     }
     if (serverGlobalParams.featureCompatibility.getVersion() >
-        ServerGlobalParams::FeatureCompatibility::Version::kFullyUpgradedTo36) {
+        ServerGlobalParams::FeatureCompatibility::Version::kFullyDowngradedTo36) {
         // If FCV 4.0, or upgrading to / downgrading from, wire version must be LATEST.
         invariant(maxWireVersion == WireVersion::LATEST_WIRE_VERSION);
     } else if (serverGlobalParams.featureCompatibility.getVersion() >
                    ServerGlobalParams::FeatureCompatibility::Version::kFullyDowngradedTo34 &&
                serverGlobalParams.featureCompatibility.getVersion() <=
-                   ServerGlobalParams::FeatureCompatibility::Version::kFullyUpgradedTo36) {
+                   ServerGlobalParams::FeatureCompatibility::Version::kFullyDowngradedTo36) {
         // If FCV 3.6, or upgrading to / downgrading from, wire version must be v3.6
         // LATEST_WIRE_VERSION or greater.
         invariant(maxWireVersion >= WireVersion::LATEST_WIRE_VERSION - 1);
diff --git a/src/mongo/db/server_options.h b/src/mongo/db/server_options.h
index 478fdbab935..e0a34ddb39c 100644
--- a/src/mongo/db/server_options.h
+++ b/src/mongo/db/server_options.h
@@ -163,7 +163,7 @@ struct ServerGlobalParams {
          *             use the 3.6 format, and existing entries may have either the
          *             3.4 or 3.6 format
          *
-         * kFullyUpgradedTo36
+         * kFullyDowngradedTo36
          * (3.6, Unset): 3.6 features are available, and new and existing storage
          *               engine entries use the 3.6 format
          *
@@ -176,9 +176,9 @@ struct ServerGlobalParams {
          * (Unset, Unset): This is the case on startup before the fCV document is
          *                 loaded into memory. isVersionInitialized() will return
          *                 false, and getVersion() will return the default
-         *                 (kFullyUpgradedTo36).
+         *                 (kFullyDowngradedTo36).
          *
-         * TODO: update this comment to 3.6/4.0 when FCV 3.4 is removed (SERVER-32597).
+         * TODO: update this comment to 3.6/4.0 when FCV 3.4 is removed (SERVER-33179).
          */
         enum class Version {
             // The order of these enums matter, higher upgrades having higher values, so that
@@ -188,7 +188,7 @@ struct ServerGlobalParams {
             kFullyDowngradedTo34 = 1,
             kDowngradingTo34 = 2,
             kUpgradingTo36 = 3,
-            kFullyUpgradedTo36 = 4,
+            kFullyDowngradedTo36 = 4,
             kDowngradingTo36 = 5,
             kUpgradingTo40 = 6,
             kFullyUpgradedTo40 = 7,
@@ -208,7 +208,7 @@ struct ServerGlobalParams {
          */
         const Version getVersion() const {
             Version v = _version.load();
-            return (v == Version::kUnsetDefault36Behavior) ? Version::kFullyUpgradedTo36 : v;
+            return (v == Version::kUnsetDefault36Behavior) ? Version::kFullyDowngradedTo36 : v;
         }
 
         void reset() {
@@ -221,7 +221,7 @@ struct ServerGlobalParams {
 
         // This determines whether to give Collections UUIDs upon creation.
         const bool isSchemaVersion36() {
-            return (getVersion() >= Version::kFullyUpgradedTo36 ||
+            return (getVersion() >= Version::kFullyDowngradedTo36 ||
                     getVersion() == Version::kUpgradingTo36);
         }
 
diff --git a/src/mongo/dbtests/dbtests.cpp b/src/mongo/dbtests/dbtests.cpp
index 77e1e4f5a48..3cf58407b53 100644
--- a/src/mongo/dbtests/dbtests.cpp
+++ b/src/mongo/dbtests/dbtests.cpp
@@ -130,7 +130,7 @@ int dbtestsMain(int argc, char** argv, char** envp) {
     mongo::dbtests::initWireSpec();
     mongo::runGlobalInitializersOrDie(argc, argv, envp);
     serverGlobalParams.featureCompatibility.setVersion(
-        ServerGlobalParams::FeatureCompatibility::Version::kFullyUpgradedTo36);
+        ServerGlobalParams::FeatureCompatibility::Version::kFullyUpgradedTo40);
     repl::ReplSettings replSettings;
     replSettings.setOplogSizeBytes(10 * 1024 * 1024);
     ServiceContext* service = getGlobalServiceContext();
diff --git a/src/mongo/s/commands/cluster_set_feature_compatibility_version_cmd.cpp b/src/mongo/s/commands/cluster_set_feature_compatibility_version_cmd.cpp
index 6897d50c498..ff753df8c69 100644
--- a/src/mongo/s/commands/cluster_set_feature_compatibility_version_cmd.cpp
+++ b/src/mongo/s/commands/cluster_set_feature_compatibility_version_cmd.cpp
@@ -41,15 +41,14 @@ namespace mongo {
 namespace {
 
 /**
- * Sets the minimum allowed version for the cluster. If it is 3.4, then shards should not use 3.6
- * features. Similarly, if 3.6, shards will not use 4.0 features.
+ * Sets the minimum allowed version for the cluster. If it is the last stable
+ * featureCompatibilityVersion, then shards will not use latest featureCompatibilityVersion
+ * features.
  *
  * Format:
  * {
  *   setFeatureCompatibilityVersion: <string version>
  * }
- *
- * TODO: update this comment when FCV 3.4 is removed (SERVER-32597).
  */
 class SetFeatureCompatibilityVersionCmd : public BasicCommand {
 public:
@@ -68,7 +67,7 @@ public:
     }
 
     std::string help() const override {
-        // TODO: update this comment when FCV 3.4 is removed (SERVER-32597).
+        // TODO: update this comment when FCV 3.4 is removed (SERVER-33179).
         return str::stream()
             << "Set the API version for the cluster. If set to \""
             << FeatureCompatibilityVersionCommandParser::kVersion34
diff --git a/src/mongo/s/server.cpp b/src/mongo/s/server.cpp
index d4673afd1cc..c03b7a920df 100644
--- a/src/mongo/s/server.cpp
+++ b/src/mongo/s/server.cpp
@@ -524,12 +524,15 @@ MONGO_INITIALIZER_GENERAL(ForkServer, ("EndStartupOptionHandling"), ("default"))
     return Status::OK();
 }
 
-// We set the featureCompatibilityVersion to 3.6 in the mongos and rely on the shards to reject
-// usages of new features if their featureCompatibilityVersion is lower.
-MONGO_INITIALIZER_WITH_PREREQUISITES(SetFeatureCompatibilityVersion36, ("EndStartupOptionStorage"))
+// Initialize the featureCompatibilityVersion server parameter since mongos does not have a
+// featureCompatibilityVersion document from which to initialize the parameter. The parameter is set
+// to the latest version because there is no feature gating that currently occurs at the mongos
+// level. The shards are responsible for rejecting usages of new features if their
+// featureCompatibilityVersion is lower.
+MONGO_INITIALIZER_WITH_PREREQUISITES(SetFeatureCompatibilityVersion40, ("EndStartupOptionStorage"))
 (InitializerContext* context) {
     serverGlobalParams.featureCompatibility.setVersion(
-        ServerGlobalParams::FeatureCompatibility::Version::kFullyUpgradedTo36);
+        ServerGlobalParams::FeatureCompatibility::Version::kFullyUpgradedTo40);
     return Status::OK();
 }
 
diff --git a/src/mongo/shell/dbshell.cpp b/src/mongo/shell/dbshell.cpp
index fea0aefc995..eef4859804a 100644
--- a/src/mongo/shell/dbshell.cpp
+++ b/src/mongo/shell/dbshell.cpp
@@ -92,12 +92,15 @@ static AtomicBool atPrompt(false);  // can eval before getting to prompt
 namespace {
 const auto kDefaultMongoURL = "mongodb://127.0.0.1:27017"_sd;
 
-// We set the featureCompatibilityVersion to 3.6 in the mongo shell and rely on the server to reject
-// usages of new features if its featureCompatibilityVersion is lower.
-MONGO_INITIALIZER_WITH_PREREQUISITES(SetFeatureCompatibilityVersion36, ("EndStartupOptionSetup"))
+// Initialize the featureCompatibilityVersion server parameter since the mongo shell does not have a
+// featureCompatibilityVersion document from which to initialize the parameter. The parameter is set
+// to the latest version because there is no feature gating that currently occurs at the mongo shell
+// level. The server is responsible for rejecting usages of new features if its
+// featureCompatibilityVersion is lower.
+MONGO_INITIALIZER_WITH_PREREQUISITES(SetFeatureCompatibilityVersion40, ("EndStartupOptionSetup"))
 (InitializerContext* context) {
     mongo::serverGlobalParams.featureCompatibility.setVersion(
-        ServerGlobalParams::FeatureCompatibility::Version::kFullyUpgradedTo36);
+        ServerGlobalParams::FeatureCompatibility::Version::kFullyUpgradedTo40);
     return Status::OK();
 }
 const auto kAuthParam = "authSource"s;