SERVER-66423 Set the fromMigrate flag of DurableReplOperation entries only when FCV is 6.0 or greater

2 files changed, 27 insertions, 6 deletions

diff --git a/src/mongo/db/op_observer_impl.cpp b/src/mongo/db/op_observer_impl.cpp
index 6b7bd4ef6a8..75a0ff101c8 100644
--- a/src/mongo/db/op_observer_impl.cpp
+++ b/src/mongo/db/op_observer_impl.cpp
@@ -548,7 +548,7 @@ void OpObserverImpl::onInserts(OperationContext* opCtx,
                             "namespace"_attr = nss,
                             "document"_attr = iter->doc);
 
-                operation.setFromMigrate(true);
+                operation.setFromMigrate_BackwardsCompatible(true);
             }
 
             txnParticipant.addTransactionOperation(opCtx, operation);
@@ -716,7 +716,8 @@ void OpObserverImpl::onUpdate(OperationContext* opCtx, const OplogUpdateEntryArg
         }
         operation.setDestinedRecipient(
             shardingWriteRouter.getReshardingDestinedRecipient(args.updateArgs->updatedDoc));
-        operation.setFromMigrateIfTrue(args.updateArgs->source == OperationSource::kFromMigrate);
+        operation.setFromMigrateIfTrue_BackwardsCompatible(args.updateArgs->source ==
+                                                           OperationSource::kFromMigrate);
         txnParticipant.addTransactionOperation(opCtx, operation);
     } else {
         MutableOplogEntry oplogEntry;
@@ -858,7 +859,7 @@ void OpObserverImpl::onDelete(OperationContext* opCtx,
     if (inBatchedWrite) {
         auto operation =
             MutableOplogEntry::makeDeleteOperation(nss, uuid, documentKey.getShardKeyAndId());
-        operation.setFromMigrateIfTrue(args.fromMigrate);
+        operation.setFromMigrateIfTrue_BackwardsCompatible(args.fromMigrate);
         batchedWriteContext.addBatchedOperation(opCtx, operation);
     } else if (inMultiDocumentTransaction) {
         const bool inRetryableInternalTransaction =
@@ -917,7 +918,7 @@ void OpObserverImpl::onDelete(OperationContext* opCtx,
         }
 
         operation.setDestinedRecipient(destinedRecipientDecoration(opCtx));
-        operation.setFromMigrateIfTrue(args.fromMigrate);
+        operation.setFromMigrateIfTrue_BackwardsCompatible(args.fromMigrate);
         txnParticipant.addTransactionOperation(opCtx, operation);
     } else {
         MutableOplogEntry oplogEntry;
diff --git a/src/mongo/db/repl/oplog_entry.h b/src/mongo/db/repl/oplog_entry.h
index 2eb195c079a..40092e47f4e 100644
--- a/src/mongo/db/repl/oplog_entry.h
+++ b/src/mongo/db/repl/oplog_entry.h
@@ -189,9 +189,29 @@ public:
         return variant_util::toVector<StmtId>(DurableReplOperation::getStatementIds());
     }
 
-    void setFromMigrateIfTrue(bool value) & {
-        if (value)
+    /**
+     * Sets the `fromMigrate` flag for the individual statement of the `applyOps` entry.
+     *
+     * During a replica set downgrade from 6.0 to 5.3, there is a window in which the primary node
+     * uses the 6.0 binary and secondaries still use the 5.3 binary. The latter are unable to parse
+     * the `fromMigrate` field, so they would assert. This function skips setting the `fromMigrate`
+     * flag to avoid compatibility problems.
+     */
+    void setFromMigrate_BackwardsCompatible(bool value) {
+        if (serverGlobalParams.featureCompatibility.isGreaterThanOrEqualTo(
+                multiversion::FeatureCompatibilityVersion::kVersion_6_0)) {
             setFromMigrate(value);
+        }
+    }
+
+    /**
+     * Same as `setFromMigrate_BackwardsCompatible` but set the `fromMigrate` flag only when the
+     * passed value is true.
+     */
+    void setFromMigrateIfTrue_BackwardsCompatible(bool value) {
+        if (value) {
+            setFromMigrate_BackwardsCompatible(true);
+        }
     }
 
 private: