SERVER-31870 Clarify 3.6 upgrade-related startup error messages

2 files changed, 14 insertions, 7 deletions

diff --git a/src/mongo/db/db.cpp b/src/mongo/db/db.cpp
index 2d191c38220..0c89f32d262 100644
--- a/src/mongo/db/db.cpp
+++ b/src/mongo/db/db.cpp
@@ -180,6 +180,10 @@ using std::endl;
 
 namespace {
 
+constexpr StringData upgradeLink = "http://dochub.mongodb.org/core/3.6-upgrade-fcv"_sd;
+constexpr StringData mustDowngradeErrorMsg =
+    "UPGRADE PROBLEM: The data files need to be fully upgraded to version 3.4 before attempting an upgrade to 3.6; see http://dochub.mongodb.org/core/3.6-upgrade-fcv for more details."_sd;
+
 Status restoreMissingFeatureCompatibilityVersionDocument(OperationContext* opCtx,
                                                          const std::vector<std::string>& dbNames) {
     bool isMmapV1 = opCtx->getServiceContext()->getGlobalStorageEngine()->isMmapV1();
@@ -204,8 +208,7 @@ Status restoreMissingFeatureCompatibilityVersionDocument(OperationContext* opCtx
     }
 
     if (!collsHaveUuids) {
-        return {ErrorCodes::MustDowngrade,
-                "Cannot restore featureCompatibilityVersion document. A 3.4 binary must be used."};
+        return {ErrorCodes::MustDowngrade, mustDowngradeErrorMsg};
     }
 
     // Restore the featureCompatibilityVersion document if it is missing.
@@ -540,8 +543,13 @@ StatusWith<bool> repairDatabasesAndCheckVersion(OperationContext* opCtx) {
                         // but with any value other than "3.4" or "3.6". This includes unexpected
                         // cases with no path forward such as the FCV value not being a string.
                         return {ErrorCodes::MustDowngrade,
-                                "Cannot parse the feature compatibility document. If you are "
-                                "trying to upgrade from 3.2, please use a 3.4 binary."};
+                                str::stream()
+                                    << "UPGRADE PROBLEM: Unable to parse the "
+                                       "featureCompatibilityVersion document. The data files need "
+                                       "to be fully upgraded to version 3.4 before attempting an "
+                                       "upgrade to 3.6. If you are upgrading to 3.6, see "
+                                    << upgradeLink
+                                    << "."};
                     }
                     fcvDocumentExists = true;
                     auto version = swVersion.getValue();
@@ -651,8 +659,7 @@ StatusWith<bool> repairDatabasesAndCheckVersion(OperationContext* opCtx) {
             }
             fassertFailedNoTrace(40652);
         } else {
-            return {ErrorCodes::MustDowngrade,
-                    "There is no feature compatibility document. A 3.4 binary must be used."};
+            return {ErrorCodes::MustDowngrade, mustDowngradeErrorMsg};
         }
     }
 
diff --git a/src/mongo/db/storage/wiredtiger/wiredtiger_kv_engine.cpp b/src/mongo/db/storage/wiredtiger/wiredtiger_kv_engine.cpp
index 82f0491aa2a..509b6864744 100644
--- a/src/mongo/db/storage/wiredtiger/wiredtiger_kv_engine.cpp
+++ b/src/mongo/db/storage/wiredtiger/wiredtiger_kv_engine.cpp
@@ -526,7 +526,7 @@ void WiredTigerKVEngine::cleanShutdown() {
             //    shipped with MongoDB 3.4 will always refuse to start up without this reconfigure
             //    being successful. Doing this last prevents MongoDB running in 3.4 with only some
             //    underlying tables being logged.
-            log() << "Downgrading files to FCV 3.4";
+            LOG(1) << "Downgrading WiredTiger tables to release compatibility 2.9";
             WT_CONNECTION* conn;
             std::stringstream openConfig;
             openConfig << _wtOpenConfig << ",log=(archive=false)";