SERVER-42910 Oplog query with higher timestamp but lower term than the sync source shouldn't time out due to afterClusterTime.

(cherry picked from commit f54709196711c63a429b71f47c584661286d675f)

2 files changed, 7 insertions, 3 deletions

diff --git a/src/mongo/db/repl/oplog_fetcher.cpp b/src/mongo/db/repl/oplog_fetcher.cpp
index 3162319ab2b..45c880be0ed 100644
--- a/src/mongo/db/repl/oplog_fetcher.cpp
+++ b/src/mongo/db/repl/oplog_fetcher.cpp
@@ -362,9 +362,9 @@ BSONObj OplogFetcher::_makeFindCommandObject(const NamespaceString& nss,
         cmdBob.append("term", term);
     }
 
-    // This ensures that the sync source never returns an empty batch of documents for the first set
-    // of results.
-    cmdBob.append("readConcern", BSON("afterClusterTime" << lastOpTimeFetched.getTimestamp()));
+    // This ensures that the sync source waits for all earlier oplog writes to be visible.
+    // Since Timestamp(0, 0) isn't allowed, Timestamp(0, 1) is the minimal we can use.
+    cmdBob.append("readConcern", BSON("afterClusterTime" << Timestamp(0, 1)));
 
     return cmdBob.obj();
 }
diff --git a/src/mongo/db/repl/replication_coordinator_impl.cpp b/src/mongo/db/repl/replication_coordinator_impl.cpp
index 56c281e251c..4f57c4ccedf 100644
--- a/src/mongo/db/repl/replication_coordinator_impl.cpp
+++ b/src/mongo/db/repl/replication_coordinator_impl.cpp
@@ -1477,6 +1477,10 @@ Status ReplicationCoordinatorImpl::_waitUntilOpTime(OperationContext* opCtx,
         // We wait only on primaries, because on secondaries, other mechanisms assure that the
         // last applied optime is always hole-free, and waiting for all earlier writes to be visible
         // can deadlock against secondary command application.
+        //
+        // Note that oplog queries by secondary nodes depend on this behavior to wait for
+        // all oplog holes to be filled in, despite providing an afterClusterTime field
+        // with Timestamp(0,1).
         _storage->waitForAllEarlierOplogWritesToBeVisible(opCtx, /* primaryOnly =*/true);
     }