SERVER-31209 Persist targetVersion in FCV document to indicate an upgrade/downgrade in progress.

1 files changed, 25 insertions, 9 deletions

diff --git a/src/mongo/db/db.cpp b/src/mongo/db/db.cpp
index 8f29f0605bc..ed3ba14e852 100644
--- a/src/mongo/db/db.cpp
+++ b/src/mongo/db/db.cpp
@@ -405,17 +405,33 @@ void repairDatabasesAndCheckVersion(OperationContext* opCtx) {
                                      versionColl,
                                      BSON("_id" << FeatureCompatibilityVersion::kParameterName),
                                      featureCompatibilityVersion)) {
-                    auto version = FeatureCompatibilityVersion::parse(featureCompatibilityVersion);
-                    if (!version.isOK()) {
-                        severe() << version.getStatus();
+                    auto swVersionInfo =
+                        FeatureCompatibilityVersion::parse(featureCompatibilityVersion);
+                    if (!swVersionInfo.isOK()) {
+                        severe() << swVersionInfo.getStatus();
                         fassertFailedNoTrace(40283);
                     }
-                    serverGlobalParams.featureCompatibility.version.store(version.getValue());
-
-                    // Update schemaVersion parameter.
-                    serverGlobalParams.featureCompatibility.isSchemaVersion36.store(
-                        serverGlobalParams.featureCompatibility.version.load() ==
-                        ServerGlobalParams::FeatureCompatibility::Version::k36);
+                    auto versionInfo = swVersionInfo.getValue();
+                    serverGlobalParams.featureCompatibility.version.store(versionInfo.version);
+                    serverGlobalParams.featureCompatibility.targetVersion.store(
+                        versionInfo.targetVersion);
+
+                    // On startup, if the targetVersion field exists, then an upgrade/downgrade
+                    // did not complete successfully.
+                    if (versionInfo.targetVersion !=
+                        ServerGlobalParams::FeatureCompatibility::Version::kUnset) {
+                        log() << "** WARNING: A featureCompatibilityVersion upgrade or downgrade "
+                                 "did not complete. "
+                              << startupWarningsLog;
+                        log() << "**          The current featureCompatibilityVersion is "
+                              << FeatureCompatibilityVersion::toString(versionInfo.version)
+                              << " and the targeted version is "
+                              << FeatureCompatibilityVersion::toString(versionInfo.targetVersion)
+                              << "." << startupWarningsLog;
+                        log() << "**          To fix this, use the setFeatureCompatibilityVersion "
+                              << "command to resume upgrade to 3.6 or downgrade to 3.4."
+                              << startupWarningsLog;
+                    }
                 }
             }
         }