SERVER-49060: added comments for generic FCV constants and conditional checks

9 files changed, 13 insertions, 0 deletions

diff --git a/src/mongo/db/catalog/coll_mod.cpp b/src/mongo/db/catalog/coll_mod.cpp
index eff12ca995c..23199627a75 100644
--- a/src/mongo/db/catalog/coll_mod.cpp
+++ b/src/mongo/db/catalog/coll_mod.cpp
@@ -208,6 +208,7 @@ StatusWith<CollModRequest> parseCollModRequest(OperationContext* opCtx,
             // being persisted in the catalog.
             boost::optional<ServerGlobalParams::FeatureCompatibility::Version>
                 maxFeatureCompatibilityVersion;
+            // (Generic FCV reference): This FCV check should exist across LTS binary versions.
             if (serverGlobalParams.validateFeaturesAsMaster.load() &&
                 currentFCV != ServerGlobalParams::FeatureCompatibility::kLatest) {
                 maxFeatureCompatibilityVersion = currentFCV;
diff --git a/src/mongo/db/catalog/database_impl.cpp b/src/mongo/db/catalog/database_impl.cpp
index f164a08e99a..7a0e74071ba 100644
--- a/src/mongo/db/catalog/database_impl.cpp
+++ b/src/mongo/db/catalog/database_impl.cpp
@@ -868,6 +868,7 @@ Status DatabaseImpl::userCreateNS(OperationContext* opCtx,
         // If the feature compatibility version is not kLatest, and we are validating features as
         // master, ban the use of new agg features introduced in kLatest to prevent them from being
         // persisted in the catalog.
+        // (Generic FCV reference): This FCV check should exist across LTS binary versions.
         if (serverGlobalParams.validateFeaturesAsMaster.load() &&
             currentFCV != ServerGlobalParams::FeatureCompatibility::kLatest) {
             expCtx->maxFeatureCompatibilityVersion = currentFCV;
diff --git a/src/mongo/db/commands/feature_compatibility_version.cpp b/src/mongo/db/commands/feature_compatibility_version.cpp
index 5c96789c300..d7f3aef5d42 100644
--- a/src/mongo/db/commands/feature_compatibility_version.cpp
+++ b/src/mongo/db/commands/feature_compatibility_version.cpp
@@ -196,6 +196,7 @@ void FeatureCompatibilityVersion::_setVersion(
     serverGlobalParams.featureCompatibility.setVersion(newVersion);
     updateMinWireVersion();
 
+    // (Generic FCV reference): This FCV check should exist across LTS binary versions.
     if (newVersion != ServerGlobalParams::FeatureCompatibility::kLastLTS) {
         // Close all incoming connections from internal clients with binary versions lower than
         // ours.
@@ -207,6 +208,7 @@ void FeatureCompatibilityVersion::_setVersion(
             .dropConnections(transport::Session::kKeepOpen);
     }
 
+    // (Generic FCV reference): This FCV check should exist across LTS binary versions.
     if (newVersion != ServerGlobalParams::FeatureCompatibility::kLatest) {
         if (MONGO_unlikely(hangBeforeAbortingRunningTransactionsOnFCVDowngrade.shouldFail())) {
             LOGV2(20460,
@@ -227,6 +229,7 @@ void FeatureCompatibilityVersion::_setVersion(
     // This can only happen in two scenarios:
     // 1. Setting featureCompatibilityVersion from downgrading to fullyDowngraded.
     // 2. Setting featureCompatibilityVersion from fullyDowngraded to upgrading.
+    // (Generic FCV reference): This FCV check should exist across LTS binary versions.
     const auto shouldIncrementTopologyVersion =
         newVersion == ServerGlobalParams::FeatureCompatibility::kLastLTS ||
         newVersion == ServerGlobalParams::FeatureCompatibility::Version::kUpgradingFrom44To451;
diff --git a/src/mongo/db/repl/initial_syncer.cpp b/src/mongo/db/repl/initial_syncer.cpp
index 687d0f65eb4..575bc0feacb 100644
--- a/src/mongo/db/repl/initial_syncer.cpp
+++ b/src/mongo/db/repl/initial_syncer.cpp
@@ -1087,6 +1087,7 @@ void InitialSyncer::_fcvFetcherCallback(const StatusWith<Fetcher::QueryResponse>
     auto version = fCVParseSW.getValue();
 
     // Changing the featureCompatibilityVersion during initial sync is unsafe.
+    // (Generic FCV reference): This FCV check should exist across LTS binary versions.
     if (version > ServerGlobalParams::FeatureCompatibility::kLastLTS &&
         version < ServerGlobalParams::FeatureCompatibility::kLatest) {
         onCompletionGuard->setResultAndCancelRemainingWork_inlock(
diff --git a/src/mongo/db/repl/oplog_applier_impl_test_fixture.cpp b/src/mongo/db/repl/oplog_applier_impl_test_fixture.cpp
index 2c6536caa44..6c05eb6cc09 100644
--- a/src/mongo/db/repl/oplog_applier_impl_test_fixture.cpp
+++ b/src/mongo/db/repl/oplog_applier_impl_test_fixture.cpp
@@ -126,6 +126,7 @@ void OplogApplierImplTest::setUp() {
     // 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.
+    // (Generic FCV reference): This FCV reference should exist across LTS binary versions.
     serverGlobalParams.featureCompatibility.setVersion(
         ServerGlobalParams::FeatureCompatibility::kLatest);
 
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 5978639a12b..94fd2d01aee 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
@@ -338,6 +338,7 @@ StatusWith<ShardType> ShardingCatalogManager::_validateHostAsShard(
                                                 << "field when attempting to add "
                                                 << connectionString.toString() << " as a shard");
     }
+    // (Generic FCV reference): This FCV check should exist across LTS binary versions.
     if (serverGlobalParams.featureCompatibility.getVersion() >
         ServerGlobalParams::FeatureCompatibility::kLastLTS) {
         // If the cluster's FCV is kLatest, or upgrading to / downgrading from, the node being added
@@ -346,6 +347,7 @@ StatusWith<ShardType> ShardingCatalogManager::_validateHostAsShard(
     } else {
         // If the cluster's FCV is kLastLTS, the node being added must be a version kLastLTS or
         // version kLatest binary.
+        // (Generic FCV reference): This FCV check should exist across LTS binary versions.
         invariant(serverGlobalParams.featureCompatibility.getVersion() ==
                   ServerGlobalParams::FeatureCompatibility::kLastLTS);
         invariant(maxWireVersion >= WireVersion::LATEST_WIRE_VERSION - 1);
diff --git a/src/mongo/db/s/sharding_mongod_test_fixture.cpp b/src/mongo/db/s/sharding_mongod_test_fixture.cpp
index c8049cd84b7..103ecc582d1 100644
--- a/src/mongo/db/s/sharding_mongod_test_fixture.cpp
+++ b/src/mongo/db/s/sharding_mongod_test_fixture.cpp
@@ -137,6 +137,7 @@ ShardingMongodTestFixture::ShardingMongodTestFixture() {
 
     // Set the highest FCV because otherwise it defaults to the lower FCV. This way we default to
     // testing this release's code, not backwards compatibility code.
+    // (Generic FCV reference): This FCV reference should exist across LTS binary versions.
     serverGlobalParams.featureCompatibility.setVersion(
         ServerGlobalParams::FeatureCompatibility::kLatest);
 }
diff --git a/src/mongo/db/server_options.h b/src/mongo/db/server_options.h
index 3be5400522a..6577d946c32 100644
--- a/src/mongo/db/server_options.h
+++ b/src/mongo/db/server_options.h
@@ -198,6 +198,8 @@ struct ServerGlobalParams {
             kVersion451 = 4,
         };
 
+        // These constants should only be used for generic FCV references. Generic references are
+        // FCV references that are expected to exist across LTS binary versions.
         static constexpr Version kLatest = Version::kVersion451;
         static constexpr Version kLastContinuous = Version::kFullyDowngradedTo44;
         static constexpr Version kLastLTS = Version::kFullyDowngradedTo44;
diff --git a/src/mongo/db/views/view_catalog.cpp b/src/mongo/db/views/view_catalog.cpp
index fb3cea60737..ad05c435d43 100644
--- a/src/mongo/db/views/view_catalog.cpp
+++ b/src/mongo/db/views/view_catalog.cpp
@@ -334,6 +334,7 @@ StatusWith<stdx::unordered_set<NamespaceString>> ViewCatalog::_validatePipeline(
     // If the feature compatibility version is not kLatest, and we are validating features as
     // master, ban the use of new agg features introduced in kLatest to prevent them from being
     // persisted in the catalog.
+    // (Generic FCV reference): This FCV check should exist across LTS binary versions.
     if (serverGlobalParams.validateFeaturesAsMaster.load() &&
         currentFCV != ServerGlobalParams::FeatureCompatibility::kLatest) {
         expCtx->maxFeatureCompatibilityVersion = currentFCV;