SERVER-27941 change the shardVersion check to an epoch check when entering the critical section.

(cherry picked from commit ce23378926659bc50604032782485c2f962c37ac)

1 files changed, 6 insertions, 4 deletions

diff --git a/src/mongo/db/s/migration_source_manager.cpp b/src/mongo/db/s/migration_source_manager.cpp
index 149a7b12397..035d21cbb82 100644
--- a/src/mongo/db/s/migration_source_manager.cpp
+++ b/src/mongo/db/s/migration_source_manager.cpp
@@ -249,16 +249,18 @@ Status MigrationSourceManager::enterCriticalSection(OperationContext* txn) {
         ScopedTransaction scopedXact(txn, MODE_IX);
         AutoGetCollection autoColl(txn, getNss(), MODE_IX, MODE_X);
 
+        // Check that the collection has not been dropped or recreated since the migration began.
         auto css = CollectionShardingState::get(txn, getNss().ns());
         auto metadata = css->getMetadata();
         if (!metadata ||
-            !metadata->getCollVersion().equals(_collectionMetadata->getCollVersion())) {
+            (metadata->getCollVersion().epoch() != _collectionMetadata->getCollVersion().epoch())) {
             return {ErrorCodes::IncompatibleShardingMetadata,
                     str::stream()
-                        << "Sharding metadata changed while holding distributed lock. Expected: "
-                        << _collectionMetadata->getCollVersion().toString()
+                        << "The collection was dropped or recreated since the migration began. "
+                        << "Expected collection epoch: "
+                        << _collectionMetadata->getCollVersion().epoch().toString()
                         << ", but found: "
-                        << (metadata ? metadata->getCollVersion().toString()
+                        << (metadata ? metadata->getCollVersion().epoch().toString()
                                      : "unsharded collection.")};
         }