1 files changed, 27 insertions, 14 deletions
diff --git a/src/mongo/db/repl/topology_coordinator_impl.cpp b/src/mongo/db/repl/topology_coordinator_impl.cpp
index e245ddb3276..afd720d7869 100644
--- a/src/mongo/db/repl/topology_coordinator_impl.cpp
+++ b/src/mongo/db/repl/topology_coordinator_impl.cpp
@@ -2228,24 +2228,37 @@ void TopologyCoordinatorImpl::processLoseElection() {
     }
 }
 
-bool TopologyCoordinatorImpl::stepDown(Date_t until, bool force, const OpTime& lastOpApplied) {
-    bool canStepDown = force;
-    for (int i = 0; !canStepDown && i < _rsConfig.getNumMembers(); ++i) {
-        if (i == _selfIndex) {
-            continue;
-        }
-        UnelectableReasonMask reason = _getUnelectableReason(i, lastOpApplied);
-        if (!reason && _hbdata[i].getAppliedOpTime() >= lastOpApplied) {
-            canStepDown = true;
-        }
+bool TopologyCoordinatorImpl::stepDown(Date_t until,
+                                       bool force,
+                                       const OpTime& lastOpApplied,
+                                       const OpTime& lastOpCommitted) {
+    // force==true overrides all other checks.
+    if (force) {
+        _stepDownUntil = until;
+        _stepDownSelfAndReplaceWith(-1);
+        return true;
     }
 
-    if (!canStepDown) {
+    // Ensure a majority of caught up nodes.
+    if (lastOpCommitted < lastOpApplied) {
         return false;
     }
-    _stepDownUntil = until;
-    _stepDownSelfAndReplaceWith(-1);
-    return true;
+
+    // Now make sure we also have at least one caught up node that is also electable.
+    for (int memberIndex = 0; memberIndex < _rsConfig.getNumMembers(); memberIndex++) {
+        // ignore your self
+        if (memberIndex == _selfIndex) {
+            continue;
+        }
+        UnelectableReasonMask reason = _getUnelectableReason(memberIndex, lastOpApplied);
+        if (!reason && _hbdata.at(memberIndex).getAppliedOpTime() >= lastOpApplied) {
+            // Found a caught up and electable node, succeed with step down.
+            _stepDownUntil = until;
+            _stepDownSelfAndReplaceWith(-1);
+            return true;
+        }
+    }
+    return false;
 }
 
 void TopologyCoordinatorImpl::setFollowerMode(MemberState::MS newMode) {