SERVER-29772 Add allowUnsafeRenamesDuringInitialSync server parameter

(cherry picked from commit 76da39708f4d07ed0cf56d986d1c6f3d4353e670)

2 files changed, 28 insertions, 3 deletions

diff --git a/src/mongo/db/repl/oplog.cpp b/src/mongo/db/repl/oplog.cpp
index 2c764baf9e3..e642142d195 100644
--- a/src/mongo/db/repl/oplog.cpp
+++ b/src/mongo/db/repl/oplog.cpp
@@ -114,6 +114,11 @@ namespace {
 Database* _localDB = nullptr;
 Collection* _localOplogCollection = nullptr;
 
+// Specifies whether we abort initial sync when attempting to apply a renameCollection operation.
+// If set to true, users risk corrupting their data. This should only be enabled by expert users
+// of the server who understand the risks this poses.
+MONGO_EXPORT_SERVER_PARAMETER(allowUnsafeRenamesDuringInitialSync, bool, false);
+
 PseudoRandom hashGenerator(std::unique_ptr<SecureRandom>(SecureRandom::create())->nextInt64());
 
 // Synchronizes the section where a new Timestamp is generated and when it actually
@@ -975,9 +980,14 @@ Status applyCommand_inlock(OperationContext* txn,
     // Applying renameCollection during initial sync might lead to data corruption, so we restart
     // the initial sync.
     if (!inSteadyStateReplication && o.firstElementFieldName() == std::string("renameCollection")) {
-        return Status(ErrorCodes::OplogOperationUnsupported,
-                      str::stream()
-                          << "Applying renameCollection not supported in initial sync: " << op);
+        if (!allowUnsafeRenamesDuringInitialSync.load()) {
+            return Status(ErrorCodes::OplogOperationUnsupported,
+                          str::stream()
+                              << "Applying renameCollection not supported in initial sync: " << op);
+        }
+        warning() << "allowUnsafeRenamesDuringInitialSync set to true. Applying renameCollection "
+                     "operation during initial sync even though it may lead to data corruption: "
+                  << op;
     }
 
     // Applying commands in repl is done under Global W-lock, so it is safe to not
diff --git a/src/mongo/db/repl/rs_initialsync.cpp b/src/mongo/db/repl/rs_initialsync.cpp
index d475d53d644..ecaea8fcbc4 100644
--- a/src/mongo/db/repl/rs_initialsync.cpp
+++ b/src/mongo/db/repl/rs_initialsync.cpp
@@ -69,6 +69,10 @@ using std::string;
 // Failpoint which fails initial sync and leaves on oplog entry in the buffer.
 MONGO_FP_DECLARE(failInitSyncWithBufferedEntriesLeft);
 
+// Failpoint which causes the initial sync function to hang before copying databases.
+MONGO_FP_DECLARE(initialSyncHangBeforeCopyingDatabases);
+
+
 /**
  * Truncates the oplog (removes any documents) and resets internal variables that were
  * originally initialized or affected by using values from the oplog at startup time.  These
@@ -346,6 +350,15 @@ Status _initialSync() {
 
     log() << "initial sync clone all databases";
 
+    if (MONGO_FAIL_POINT(initialSyncHangBeforeCopyingDatabases)) {
+        // This log output is used in js tests so please leave it.
+        log() << "initial sync - initialSyncHangBeforeCopyingDatabases fail point "
+                 "enabled. Blocking until fail point is disabled.";
+        while (MONGO_FAIL_POINT(initialSyncHangBeforeCopyingDatabases) && !inShutdown()) {
+            mongo::sleepsecs(1);
+        }
+    }
+
     list<string> dbs = r.conn()->getDatabaseNames();
     {
         // Clone admin database first, to catch schema errors.
@@ -511,6 +524,8 @@ void syncDoInitialSync() {
         severe() << "The maximum number of retries have been exhausted for initial sync.";
         fassertFailedNoTrace(16233);
     }
+
+    log() << "initial sync succeeded after " << (failedAttempts + 1) << " attempt(s).";
 }
 
 }  // namespace repl