SERVER-32630 Ensure the fCV parameter is initialized before reading

12 files changed, 91 insertions, 71 deletions

diff --git a/src/mongo/db/catalog/database_impl.cpp b/src/mongo/db/catalog/database_impl.cpp
index ebbe30aee40..e6cc8ef537c 100644
--- a/src/mongo/db/catalog/database_impl.cpp
+++ b/src/mongo/db/catalog/database_impl.cpp
@@ -814,8 +814,10 @@ Collection* DatabaseImpl::createCollection(OperationContext* opCtx,
         if (collection->requiresIdIndex()) {
             if (optionsWithUUID.autoIndexId == CollectionOptions::YES ||
                 optionsWithUUID.autoIndexId == CollectionOptions::DEFAULT) {
+                // createCollection() may be called before the in-memory fCV parameter is
+                // initialized, so use the unsafe fCV getter here.
                 const auto featureCompatibilityVersion =
-                    serverGlobalParams.featureCompatibility.getVersion();
+                    serverGlobalParams.featureCompatibility.getVersionUnsafe();
                 IndexCatalog* ic = collection->getIndexCatalog();
                 fullIdIndexSpec = uassertStatusOK(ic->createIndexOnEmptyCollection(
                     opCtx,
diff --git a/src/mongo/db/catalog/index_spec_validate_test.cpp b/src/mongo/db/catalog/index_spec_validate_test.cpp
index 9af8fa54b01..44f4e48b32c 100644
--- a/src/mongo/db/catalog/index_spec_validate_test.cpp
+++ b/src/mongo/db/catalog/index_spec_validate_test.cpp
@@ -40,6 +40,7 @@
 #include "mongo/db/namespace_string.h"
 #include "mongo/db/query/collation/collator_interface_mock.h"
 #include "mongo/db/query/query_test_service_context.h"
+#include "mongo/db/server_options.h"
 #include "mongo/unittest/unittest.h"
 
 namespace mongo {
@@ -49,7 +50,6 @@ using index_key_validate::validateIndexSpec;
 using index_key_validate::validateIdIndexSpec;
 using index_key_validate::validateIndexSpecCollation;
 
-const ServerGlobalParams::FeatureCompatibility defaultFeatureCompatibility{};
 const NamespaceString kTestNamespace("test", "index_spec_validate");
 constexpr OperationContext* kDefaultOpCtx = nullptr;
 
@@ -71,7 +71,7 @@ TEST(IndexSpecValidateTest, ReturnsAnErrorIfKeyPatternIsNotAnObject) {
                                 BSON("key" << 1 << "name"
                                            << "indexName"),
                                 kTestNamespace,
-                                defaultFeatureCompatibility));
+                                serverGlobalParams.featureCompatibility));
     ASSERT_EQ(ErrorCodes::TypeMismatch,
               validateIndexSpec(kDefaultOpCtx,
                                 BSON("key"
@@ -79,13 +79,13 @@ TEST(IndexSpecValidateTest, ReturnsAnErrorIfKeyPatternIsNotAnObject) {
                                      << "name"
                                      << "indexName"),
                                 kTestNamespace,
-                                defaultFeatureCompatibility));
+                                serverGlobalParams.featureCompatibility));
     ASSERT_EQ(ErrorCodes::TypeMismatch,
               validateIndexSpec(kDefaultOpCtx,
                                 BSON("key" << BSONArray() << "name"
                                            << "indexName"),
                                 kTestNamespace,
-                                defaultFeatureCompatibility));
+                                serverGlobalParams.featureCompatibility));
 }
 
 TEST(IndexSpecValidateTest, ReturnsAnErrorIfFieldRepeatedInKeyPattern) {
@@ -94,7 +94,7 @@ TEST(IndexSpecValidateTest, ReturnsAnErrorIfFieldRepeatedInKeyPattern) {
                                 BSON("key" << BSON("field" << 1 << "field" << 1) << "name"
                                            << "indexName"),
                                 kTestNamespace,
-                                defaultFeatureCompatibility));
+                                serverGlobalParams.featureCompatibility));
     ASSERT_EQ(ErrorCodes::BadValue,
               validateIndexSpec(kDefaultOpCtx,
                                 BSON("key" << BSON("field" << 1 << "otherField" << -1 << "field"
@@ -102,7 +102,7 @@ TEST(IndexSpecValidateTest, ReturnsAnErrorIfFieldRepeatedInKeyPattern) {
                                            << "name"
                                            << "indexName"),
                                 kTestNamespace,
-                                defaultFeatureCompatibility));
+                                serverGlobalParams.featureCompatibility));
 }
 
 TEST(IndexSpecValidateTest, ReturnsAnErrorIfKeyPatternIsNotPresent) {
@@ -111,7 +111,7 @@ TEST(IndexSpecValidateTest, ReturnsAnErrorIfKeyPatternIsNotPresent) {
                                 BSON("name"
                                      << "indexName"),
                                 kTestNamespace,
-                                defaultFeatureCompatibility));
+                                serverGlobalParams.featureCompatibility));
 }
 
 TEST(IndexSpecValidateTest, ReturnsAnErrorIfNameIsNotAString) {
@@ -119,7 +119,7 @@ TEST(IndexSpecValidateTest, ReturnsAnErrorIfNameIsNotAString) {
               validateIndexSpec(kDefaultOpCtx,
                                 BSON("key" << BSON("field" << 1) << "name" << 1),
                                 kTestNamespace,
-                                defaultFeatureCompatibility));
+                                serverGlobalParams.featureCompatibility));
 }
 
 TEST(IndexSpecValidateTest, ReturnsAnErrorIfNameIsNotPresent) {
@@ -127,7 +127,7 @@ TEST(IndexSpecValidateTest, ReturnsAnErrorIfNameIsNotPresent) {
               validateIndexSpec(kDefaultOpCtx,
                                 BSON("key" << BSON("field" << 1)),
                                 kTestNamespace,
-                                defaultFeatureCompatibility));
+                                serverGlobalParams.featureCompatibility));
 }
 
 TEST(IndexSpecValidateTest, ReturnsAnErrorIfNamespaceIsNotAString) {
@@ -138,7 +138,7 @@ TEST(IndexSpecValidateTest, ReturnsAnErrorIfNamespaceIsNotAString) {
                                            << "ns"
                                            << 1),
                                 kTestNamespace,
-                                defaultFeatureCompatibility));
+                                serverGlobalParams.featureCompatibility));
     ASSERT_EQ(ErrorCodes::TypeMismatch,
               validateIndexSpec(kDefaultOpCtx,
                                 BSON("key" << BSON("field" << 1) << "name"
@@ -146,7 +146,7 @@ TEST(IndexSpecValidateTest, ReturnsAnErrorIfNamespaceIsNotAString) {
                                            << "ns"
                                            << BSONObj()),
                                 kTestNamespace,
-                                defaultFeatureCompatibility));
+                                serverGlobalParams.featureCompatibility));
 }
 
 TEST(IndexSpecValidateTest, ReturnsAnErrorIfNamespaceIsEmptyString) {
@@ -157,7 +157,7 @@ TEST(IndexSpecValidateTest, ReturnsAnErrorIfNamespaceIsEmptyString) {
                                            << "ns"
                                            << ""),
                                 NamespaceString(),
-                                defaultFeatureCompatibility));
+                                serverGlobalParams.featureCompatibility));
 }
 
 TEST(IndexSpecValidateTest, ReturnsAnErrorIfNamespaceDoesNotMatch) {
@@ -168,7 +168,7 @@ TEST(IndexSpecValidateTest, ReturnsAnErrorIfNamespaceDoesNotMatch) {
                                            << "ns"
                                            << "some string"),
                                 kTestNamespace,
-                                defaultFeatureCompatibility));
+                                serverGlobalParams.featureCompatibility));
 
     // Verify that we reject the index specification when the "ns" field only contains the
     // collection name.
@@ -179,7 +179,7 @@ TEST(IndexSpecValidateTest, ReturnsAnErrorIfNamespaceDoesNotMatch) {
                                            << "ns"
                                            << kTestNamespace.coll()),
                                 kTestNamespace,
-                                defaultFeatureCompatibility));
+                                serverGlobalParams.featureCompatibility));
 }
 
 TEST(IndexSpecValidateTest, ReturnsIndexSpecWithNamespaceFilledInIfItIsNotPresent) {
@@ -189,7 +189,7 @@ TEST(IndexSpecValidateTest, ReturnsIndexSpecWithNamespaceFilledInIfItIsNotPresen
                                                << "v"
                                                << 1),
                                     kTestNamespace,
-                                    defaultFeatureCompatibility);
+                                    serverGlobalParams.featureCompatibility);
     ASSERT_OK(result.getStatus());
 
     // We don't care about the order of the fields in the resulting index specification.
@@ -203,7 +203,7 @@ TEST(IndexSpecValidateTest, ReturnsIndexSpecWithNamespaceFilledInIfItIsNotPresen
 
     // Verify that the index specification we returned is still considered valid.
     ASSERT_OK(validateIndexSpec(
-        kDefaultOpCtx, result.getValue(), kTestNamespace, defaultFeatureCompatibility));
+        kDefaultOpCtx, result.getValue(), kTestNamespace, serverGlobalParams.featureCompatibility));
 }
 
 TEST(IndexSpecValidateTest, ReturnsIndexSpecUnchangedIfNamespaceAndVersionArePresent) {
@@ -215,7 +215,7 @@ TEST(IndexSpecValidateTest, ReturnsIndexSpecUnchangedIfNamespaceAndVersionArePre
                                                << "v"
                                                << 1),
                                     kTestNamespace,
-                                    defaultFeatureCompatibility);
+                                    serverGlobalParams.featureCompatibility);
     ASSERT_OK(result.getStatus());
 
     // We don't care about the order of the fields in the resulting index specification.
@@ -236,7 +236,7 @@ TEST(IndexSpecValidateTest, ReturnsAnErrorIfVersionIsNotANumber) {
                                            << "v"
                                            << "not a number"),
                                 kTestNamespace,
-                                defaultFeatureCompatibility));
+                                serverGlobalParams.featureCompatibility));
     ASSERT_EQ(ErrorCodes::TypeMismatch,
               validateIndexSpec(kDefaultOpCtx,
                                 BSON("key" << BSON("field" << 1) << "name"
@@ -244,7 +244,7 @@ TEST(IndexSpecValidateTest, ReturnsAnErrorIfVersionIsNotANumber) {
                                            << "v"
                                            << BSONObj()),
                                 kTestNamespace,
-                                defaultFeatureCompatibility));
+                                serverGlobalParams.featureCompatibility));
 }
 
 TEST(IndexSpecValidateTest, ReturnsAnErrorIfVersionIsNotRepresentableAsInt) {
@@ -255,7 +255,7 @@ TEST(IndexSpecValidateTest, ReturnsAnErrorIfVersionIsNotRepresentableAsInt) {
                                            << "v"
                                            << 2.2),
                                 kTestNamespace,
-                                defaultFeatureCompatibility));
+                                serverGlobalParams.featureCompatibility));
     ASSERT_EQ(ErrorCodes::BadValue,
               validateIndexSpec(kDefaultOpCtx,
                                 BSON("key" << BSON("field" << 1) << "name"
@@ -263,7 +263,7 @@ TEST(IndexSpecValidateTest, ReturnsAnErrorIfVersionIsNotRepresentableAsInt) {
                                            << "v"
                                            << std::nan("1")),
                                 kTestNamespace,
-                                defaultFeatureCompatibility));
+                                serverGlobalParams.featureCompatibility));
     ASSERT_EQ(ErrorCodes::BadValue,
               validateIndexSpec(kDefaultOpCtx,
                                 BSON("key" << BSON("field" << 1) << "name"
@@ -271,7 +271,7 @@ TEST(IndexSpecValidateTest, ReturnsAnErrorIfVersionIsNotRepresentableAsInt) {
                                            << "v"
                                            << std::numeric_limits<double>::infinity()),
                                 kTestNamespace,
-                                defaultFeatureCompatibility));
+                                serverGlobalParams.featureCompatibility));
     ASSERT_EQ(ErrorCodes::BadValue,
               validateIndexSpec(kDefaultOpCtx,
                                 BSON("key" << BSON("field" << 1) << "name"
@@ -279,7 +279,7 @@ TEST(IndexSpecValidateTest, ReturnsAnErrorIfVersionIsNotRepresentableAsInt) {
                                            << "v"
                                            << std::numeric_limits<long long>::max()),
                                 kTestNamespace,
-                                defaultFeatureCompatibility));
+                                serverGlobalParams.featureCompatibility));
 }
 
 TEST(IndexSpecValidateTest, ReturnsAnErrorIfVersionIsV0) {
@@ -290,7 +290,7 @@ TEST(IndexSpecValidateTest, ReturnsAnErrorIfVersionIsV0) {
                                            << "v"
                                            << 0),
                                 kTestNamespace,
-                                defaultFeatureCompatibility));
+                                serverGlobalParams.featureCompatibility));
 }
 
 TEST(IndexSpecValidateTest, ReturnsAnErrorIfVersionIsUnsupported) {
@@ -304,7 +304,7 @@ TEST(IndexSpecValidateTest, ReturnsAnErrorIfVersionIsUnsupported) {
                                            << BSON("locale"
                                                    << "en")),
                                 kTestNamespace,
-                                defaultFeatureCompatibility));
+                                serverGlobalParams.featureCompatibility));
 
     ASSERT_EQ(ErrorCodes::CannotCreateIndex,
               validateIndexSpec(kDefaultOpCtx,
@@ -313,7 +313,7 @@ TEST(IndexSpecValidateTest, ReturnsAnErrorIfVersionIsUnsupported) {
                                            << "v"
                                            << -3LL),
                                 kTestNamespace,
-                                defaultFeatureCompatibility));
+                                serverGlobalParams.featureCompatibility));
 }
 
 TEST(IndexSpecValidateTest, AcceptsIndexVersionsThatAreAllowedForCreation) {
@@ -323,7 +323,7 @@ TEST(IndexSpecValidateTest, AcceptsIndexVersionsThatAreAllowedForCreation) {
                                                << "v"
                                                << 1),
                                     kTestNamespace,
-                                    defaultFeatureCompatibility);
+                                    serverGlobalParams.featureCompatibility);
     ASSERT_OK(result.getStatus());
 
     // We don't care about the order of the fields in the resulting index specification.
@@ -341,7 +341,7 @@ TEST(IndexSpecValidateTest, AcceptsIndexVersionsThatAreAllowedForCreation) {
                                           << "v"
                                           << 2LL),
                                kTestNamespace,
-                               defaultFeatureCompatibility);
+                               serverGlobalParams.featureCompatibility);
     ASSERT_OK(result.getStatus());
 
     // We don't care about the order of the fields in the resulting index specification.
@@ -361,7 +361,7 @@ TEST(IndexSpecValidateTest, DefaultIndexVersionIsV2) {
                                                << "ns"
                                                << kTestNamespace.ns()),
                                     kTestNamespace,
-                                    defaultFeatureCompatibility);
+                                    serverGlobalParams.featureCompatibility);
     ASSERT_OK(result.getStatus());
 
     // We don't care about the order of the fields in the resulting index specification.
@@ -375,7 +375,7 @@ TEST(IndexSpecValidateTest, DefaultIndexVersionIsV2) {
 
     // Verify that the index specification we returned is still considered valid.
     ASSERT_OK(validateIndexSpec(
-        kDefaultOpCtx, result.getValue(), kTestNamespace, defaultFeatureCompatibility));
+        kDefaultOpCtx, result.getValue(), kTestNamespace, serverGlobalParams.featureCompatibility));
 }
 
 TEST(IndexSpecValidateTest, AcceptsIndexVersionV1) {
@@ -385,7 +385,7 @@ TEST(IndexSpecValidateTest, AcceptsIndexVersionV1) {
                                                << "v"
                                                << 1),
                                     kTestNamespace,
-                                    defaultFeatureCompatibility);
+                                    serverGlobalParams.featureCompatibility);
     ASSERT_OK(result.getStatus());
 
     // We don't care about the order of the fields in the resulting index specification.
@@ -399,17 +399,13 @@ TEST(IndexSpecValidateTest, AcceptsIndexVersionV1) {
 }
 
 TEST(IndexSpecValidateTest, AcceptsIndexVersionV2Unique) {
-    ServerGlobalParams::FeatureCompatibility featureCompatibility;
-    featureCompatibility.setVersion(
-        ServerGlobalParams::FeatureCompatibility::Version::kFullyUpgradedTo40);
-
     auto result = validateIndexSpec(kDefaultOpCtx,
                                     BSON("key" << BSON("field" << 1) << "name"
                                                << "indexName"
                                                << "v"
                                                << 3),
                                     kTestNamespace,
-                                    featureCompatibility);
+                                    serverGlobalParams.featureCompatibility);
     ASSERT_OK(result.getStatus());
 
     // We don't care about the order of the fields in the resulting index specification.
@@ -420,7 +416,6 @@ TEST(IndexSpecValidateTest, AcceptsIndexVersionV2Unique) {
                                         << "v"
                                         << 3)),
                       sorted(result.getValue()));
-    featureCompatibility.reset();
 }
 TEST(IndexSpecValidateTest, ReturnsAnErrorIfCollationIsNotAnObject) {
     ASSERT_EQ(ErrorCodes::TypeMismatch,
@@ -430,7 +425,7 @@ TEST(IndexSpecValidateTest, ReturnsAnErrorIfCollationIsNotAnObject) {
                                            << "collation"
                                            << 1),
                                 kTestNamespace,
-                                defaultFeatureCompatibility));
+                                serverGlobalParams.featureCompatibility));
     ASSERT_EQ(ErrorCodes::TypeMismatch,
               validateIndexSpec(kDefaultOpCtx,
                                 BSON("key" << BSON("field" << 1) << "name"
@@ -438,7 +433,7 @@ TEST(IndexSpecValidateTest, ReturnsAnErrorIfCollationIsNotAnObject) {
                                            << "collation"
                                            << "not an object"),
                                 kTestNamespace,
-                                defaultFeatureCompatibility));
+                                serverGlobalParams.featureCompatibility));
     ASSERT_EQ(ErrorCodes::TypeMismatch,
               validateIndexSpec(kDefaultOpCtx,
                                 BSON("key" << BSON("field" << 1) << "name"
@@ -446,7 +441,7 @@ TEST(IndexSpecValidateTest, ReturnsAnErrorIfCollationIsNotAnObject) {
                                            << "collation"
                                            << BSONArray()),
                                 kTestNamespace,
-                                defaultFeatureCompatibility));
+                                serverGlobalParams.featureCompatibility));
 }
 
 TEST(IndexSpecValidateTest, ReturnsAnErrorIfCollationIsEmpty) {
@@ -457,7 +452,7 @@ TEST(IndexSpecValidateTest, ReturnsAnErrorIfCollationIsEmpty) {
                                            << "collation"
                                            << BSONObj()),
                                 kTestNamespace,
-                                defaultFeatureCompatibility));
+                                serverGlobalParams.featureCompatibility));
 }
 
 TEST(IndexSpecValidateTest, ReturnsAnErrorIfCollationIsPresentAndVersionIsLessThanV2) {
@@ -471,7 +466,7 @@ TEST(IndexSpecValidateTest, ReturnsAnErrorIfCollationIsPresentAndVersionIsLessTh
                                            << "v"
                                            << 1),
                                 kTestNamespace,
-                                defaultFeatureCompatibility));
+                                serverGlobalParams.featureCompatibility));
 }
 
 TEST(IndexSpecValidateTest, AcceptsAnyNonEmptyObjectValueForCollation) {
@@ -484,7 +479,7 @@ TEST(IndexSpecValidateTest, AcceptsAnyNonEmptyObjectValueForCollation) {
                                                << BSON("locale"
                                                        << "simple")),
                                     kTestNamespace,
-                                    defaultFeatureCompatibility);
+                                    serverGlobalParams.featureCompatibility);
     ASSERT_OK(result.getStatus());
 
     // We don't care about the order of the fields in the resulting index specification.
@@ -507,7 +502,7 @@ TEST(IndexSpecValidateTest, AcceptsAnyNonEmptyObjectValueForCollation) {
                                           << "collation"
                                           << BSON("unknownCollationOption" << true)),
                                kTestNamespace,
-                               defaultFeatureCompatibility);
+                               serverGlobalParams.featureCompatibility);
     ASSERT_OK(result.getStatus());
 
     // We don't care about the order of the fields in the resulting index specification.
@@ -532,7 +527,7 @@ TEST(IndexSpecValidateTest, AcceptsIndexSpecIfCollationIsPresentAndVersionIsEqua
                                                << BSON("locale"
                                                        << "en")),
                                     kTestNamespace,
-                                    defaultFeatureCompatibility);
+                                    serverGlobalParams.featureCompatibility);
     ASSERT_OK(result.getStatus());
 
     // We don't care about the order of the fields in the resulting index specification.
@@ -557,7 +552,7 @@ TEST(IndexSpecValidateTest, ReturnsAnErrorIfUnknownFieldIsPresentInSpecV2) {
                                                << "unknownField"
                                                << 1),
                                     kTestNamespace,
-                                    defaultFeatureCompatibility);
+                                    serverGlobalParams.featureCompatibility);
     ASSERT_EQ(ErrorCodes::InvalidIndexSpecificationOption, result);
 }
 
@@ -570,7 +565,7 @@ TEST(IndexSpecValidateTest, ReturnsAnErrorIfUnknownFieldIsPresentInSpecV1) {
                                                << "unknownField"
                                                << 1),
                                     kTestNamespace,
-                                    defaultFeatureCompatibility);
+                                    serverGlobalParams.featureCompatibility);
     ASSERT_EQ(ErrorCodes::InvalidIndexSpecificationOption, result);
 }
 
@@ -802,7 +797,7 @@ TEST(IndexSpecPartialFilterTest, FailsIfPartialFilterIsNotAnObject) {
                                                << "partialFilterExpression"
                                                << 1),
                                     kTestNamespace,
-                                    defaultFeatureCompatibility);
+                                    serverGlobalParams.featureCompatibility);
     ASSERT_EQ(result.getStatus(), ErrorCodes::TypeMismatch);
 }
 
@@ -813,7 +808,7 @@ TEST(IndexSpecPartialFilterTest, FailsIfPartialFilterContainsBannedFeature) {
                                                << "partialFilterExpression"
                                                << BSON("$isolated" << 1)),
                                     kTestNamespace,
-                                    defaultFeatureCompatibility);
+                                    serverGlobalParams.featureCompatibility);
     ASSERT_EQ(result.getStatus(), ErrorCodes::QueryFeatureNotAllowed);
 }
 
@@ -824,7 +819,7 @@ TEST(IndexSpecPartialFilterTest, AcceptsValidPartialFilterExpression) {
                                                << "partialFilterExpression"
                                                << BSON("a" << 1)),
                                     kTestNamespace,
-                                    defaultFeatureCompatibility);
+                                    serverGlobalParams.featureCompatibility);
     ASSERT_OK(result.getStatus());
 }
 
diff --git a/src/mongo/db/commands/feature_compatibility_version.cpp b/src/mongo/db/commands/feature_compatibility_version.cpp
index 43c4bbd4d6a..e9b98c38c63 100644
--- a/src/mongo/db/commands/feature_compatibility_version.cpp
+++ b/src/mongo/db/commands/feature_compatibility_version.cpp
@@ -147,8 +147,10 @@ void FeatureCompatibilityVersion::onInsertOrUpdate(OperationContext* opCtx, cons
 
     // To avoid extra log messages when the targetVersion is set/unset, only log when the version
     // changes.
-    auto oldVersion = serverGlobalParams.featureCompatibility.getVersion();
-    if (oldVersion != newVersion) {
+    bool isDifferent = serverGlobalParams.featureCompatibility.isVersionInitialized()
+        ? serverGlobalParams.featureCompatibility.getVersion() != newVersion
+        : true;
+    if (isDifferent) {
         log() << "setting featureCompatibilityVersion to "
               << FeatureCompatibilityVersionParser::toString(newVersion);
     }
diff --git a/src/mongo/db/db.cpp b/src/mongo/db/db.cpp
index 683d2f3e347..d52ef2343f2 100644
--- a/src/mongo/db/db.cpp
+++ b/src/mongo/db/db.cpp
@@ -839,10 +839,12 @@ void shutdownTask() {
             opCtx = uniqueOpCtx.get();
         }
 
-        if (serverGlobalParams.featureCompatibility.getVersion() !=
-            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'.
+        if (serverGlobalParams.featureCompatibility.isVersionInitialized() &&
+            serverGlobalParams.featureCompatibility.getVersion() ==
+                ServerGlobalParams::FeatureCompatibility::Version::kFullyDowngradedTo36) {
+            // If we are fully downgraded, drop the 'checkpointTimestamp' collection. Otherwise a
+            // 3.6 binary can apply operations without updating the 'checkpointTimestamp',
+            // corrupting data.
             log(LogComponent::kReplication)
                 << "shutdown: removing checkpointTimestamp collection...";
             Status status =
diff --git a/src/mongo/db/repl/replication_coordinator_impl.cpp b/src/mongo/db/repl/replication_coordinator_impl.cpp
index a794d12932e..07acdf5be45 100644
--- a/src/mongo/db/repl/replication_coordinator_impl.cpp
+++ b/src/mongo/db/repl/replication_coordinator_impl.cpp
@@ -2535,10 +2535,11 @@ ReplicationCoordinatorImpl::_updateMemberStateFromTopologyCoordinator_inlock(
     }
 
     log() << "transition to " << newState << " from " << _memberState << rsLog;
-    // Initializes the featureCompatibilityVersion to the default value, because arbiters do not
-    // receive the replicated version.
+    // Initializes the featureCompatibilityVersion to the latest value, because arbiters do not
+    // receive the replicated version. This is to avoid bugs like SERVER-32639.
     if (newState.arbiter()) {
-        serverGlobalParams.featureCompatibility.reset();
+        serverGlobalParams.featureCompatibility.setVersion(
+            ServerGlobalParams::FeatureCompatibility::Version::kFullyUpgradedTo40);
     }
 
     _memberState = newState;
diff --git a/src/mongo/db/server_options.h b/src/mongo/db/server_options.h
index 7c146b7b063..5e4e934e2b0 100644
--- a/src/mongo/db/server_options.h
+++ b/src/mongo/db/server_options.h
@@ -199,10 +199,21 @@ struct ServerGlobalParams {
         }
 
         /**
-         * This safe getter for the featureCompatibilityVersion returns a default value when the
-         * version has not yet been set.
+         * This safe getter for the featureCompatibilityVersion parameter ensures the parameter has
+         * been initialized with a meaningful value.
          */
         const Version getVersion() const {
+            invariant(isVersionInitialized());
+            return _version.load();
+        }
+
+        /**
+         * This unsafe getter for the featureCompatibilityVersion parameter returns the last-stable
+         * featureCompatibilityVersion value if the parameter has not yet been initialized with a
+         * meaningful value. This getter should only be used if the parameter is intentionally read
+         * prior to the creation/parsing of the featureCompatibilityVersion document.
+         */
+        const Version getVersionUnsafe() const {
             Version v = _version.load();
             return (v == Version::kUnsetDefault36Behavior) ? Version::kFullyDowngradedTo36 : v;
         }
diff --git a/src/mongo/db/service_context_d_test_fixture.cpp b/src/mongo/db/service_context_d_test_fixture.cpp
index 4f69e5eb7b9..d42641381e9 100644
--- a/src/mongo/db/service_context_d_test_fixture.cpp
+++ b/src/mongo/db/service_context_d_test_fixture.cpp
@@ -51,6 +51,7 @@
 namespace mongo {
 
 void ServiceContextMongoDTest::setUp() {
+    Test::setUp();
     Client::initThread(getThreadName());
 
     auto const serviceContext = getServiceContext();
@@ -86,6 +87,7 @@ void ServiceContextMongoDTest::tearDown() {
     ON_BLOCK_EXIT([&] { Client::destroy(); });
     auto opCtx = cc().makeOperationContext();
     _dropAllDBs(opCtx.get());
+    Test::tearDown();
 }
 
 ServiceContext* ServiceContextMongoDTest::getServiceContext() {
diff --git a/src/mongo/db/storage/wiredtiger/wiredtiger_kv_engine.cpp b/src/mongo/db/storage/wiredtiger/wiredtiger_kv_engine.cpp
index a3381606ecf..a365149462e 100644
--- a/src/mongo/db/storage/wiredtiger/wiredtiger_kv_engine.cpp
+++ b/src/mongo/db/storage/wiredtiger/wiredtiger_kv_engine.cpp
@@ -513,13 +513,8 @@ void WiredTigerKVEngine::cleanShutdown() {
         // state is set. One is when `EncryptionHooks::restartRequired` is true. The other is when
         // the server shuts down because it refuses to acknowledge an FCV value more than one
         // version behind (e.g: 4.0 errors when reading 3.4).
-        //
-        // In the first case, we ideally do not perform a file format downgrade (but it is
-        // acceptable). In the second, the server must downgrade to allow a 3.6 binary to start
-        // up. Ideally, our internal FCV value would allow for older values, even if only to
-        // immediately shutdown. This would allow downstream logic, such as this method, to make
-        // an informed decision.
         const bool needsDowngrade = !_readOnly &&
+            serverGlobalParams.featureCompatibility.isVersionInitialized() &&
             serverGlobalParams.featureCompatibility.getVersion() ==
                 ServerGlobalParams::FeatureCompatibility::Version::kFullyDowngradedTo36;
 
diff --git a/src/mongo/db/views/view_catalog_test.cpp b/src/mongo/db/views/view_catalog_test.cpp
index b18b5a4780d..8e811f3827a 100644
--- a/src/mongo/db/views/view_catalog_test.cpp
+++ b/src/mongo/db/views/view_catalog_test.cpp
@@ -131,6 +131,7 @@ protected:
 class ReplViewCatalogFixture : public ViewCatalogFixture {
 public:
     void setUp() override {
+        Test::setUp();
         auto service = getServiceContext();
         repl::ReplSettings settings;
 
diff --git a/src/mongo/unittest/SConscript b/src/mongo/unittest/SConscript
index b4e137ff4b9..50c94ac7abf 100644
--- a/src/mongo/unittest/SConscript
+++ b/src/mongo/unittest/SConscript
@@ -14,6 +14,7 @@ env.Library(target="unittest",
             ],
             LIBDEPS=[
                 '$BUILD_DIR/mongo/base',
+                '$BUILD_DIR/mongo/db/server_options_core',
                 '$BUILD_DIR/mongo/util/options_parser/options_parser',
             ])
 
diff --git a/src/mongo/unittest/unittest.cpp b/src/mongo/unittest/unittest.cpp
index fa5f177da61..9a87664f4c9 100644
--- a/src/mongo/unittest/unittest.cpp
+++ b/src/mongo/unittest/unittest.cpp
@@ -37,6 +37,7 @@
 
 #include "mongo/base/checked_cast.h"
 #include "mongo/base/init.h"
+#include "mongo/db/server_options.h"
 #include "mongo/logger/console_appender.h"
 #include "mongo/logger/log_manager.h"
 #include "mongo/logger/logger.h"
@@ -179,8 +180,15 @@ void Test::run() {
     }
 }
 
-void Test::setUp() {}
-void Test::tearDown() {}
+// Attempting to read the featureCompatibilityVersion parameter before it is explicitly initialized
+// with a meaningful value will trigger failures as of SERVER-32630.
+void Test::setUp() {
+    serverGlobalParams.featureCompatibility.setVersion(
+        ServerGlobalParams::FeatureCompatibility::Version::kFullyUpgradedTo40);
+}
+void Test::tearDown() {
+    serverGlobalParams.featureCompatibility.reset();
+}
 
 namespace {
 class StringVectorAppender : public logger::MessageLogDomain::EventAppender {
diff --git a/src/mongo/unittest/unittest.h b/src/mongo/unittest/unittest.h
index 44b1e68846c..1a41f7acbf3 100644
--- a/src/mongo/unittest/unittest.h
+++ b/src/mongo/unittest/unittest.h
@@ -344,7 +344,6 @@ protected:
      */
     void printCapturedLogLines() const;
 
-private:
     /**
      * Called on the test object before running the test.
      */
@@ -355,6 +354,7 @@ private:
      */
     virtual void tearDown();
 
+private:
     /**
      * The test itself.
      */