2 files changed, 44 insertions, 7 deletions

diff --git a/src/mongo/db/repl/replication_coordinator_impl.cpp b/src/mongo/db/repl/replication_coordinator_impl.cpp
index 2ea7ee7b3fb..9b6e53ef76f 100644
--- a/src/mongo/db/repl/replication_coordinator_impl.cpp
+++ b/src/mongo/db/repl/replication_coordinator_impl.cpp
@@ -1036,9 +1036,17 @@ void ReplicationCoordinatorImpl::_setMyLastAppliedOpTime_inlock(const OpTime& op
     _updateLastCommittedOpTime_inlock();
 
     // Add the new applied timestamp to the list of stable timestamp candidates and then set the
-    // last stable timestamp.
-    _stableTimestampCandidates.insert(opTime.getTimestamp());
-    _setStableTimestampForStorage_inlock();
+    // last stable timestamp. Stable timestamps are used to determine the last timestamp that it is
+    // safe to revert the database to, in the event of a rollback. Note that master-slave mode has
+    // no automatic fail over, and so rollbacks never occur. Additionally, the commit point for a
+    // master-slave set will never advance, since it doesn't use any consensus protocol. Since the
+    // set of stable timestamp candidates can only get cleaned up when the commit point advances, we
+    // should refrain from updating stable timestamp candidates in master-slave mode, to avoid the
+    // candidates list from growing unbounded.
+    if (getReplicationMode() == Mode::modeReplSet) {
+        _stableTimestampCandidates.insert(opTime.getTimestamp());
+        _setStableTimestampForStorage_inlock();
+    }
 
     _opTimeWaiterList.signalAndRemoveIf_inlock(
         [opTime](Waiter* waiter) { return waiter->opTime <= opTime; });
diff --git a/src/mongo/db/repl/replication_coordinator_impl_test.cpp b/src/mongo/db/repl/replication_coordinator_impl_test.cpp
index babe8fdbc42..9a7ed34f44e 100644
--- a/src/mongo/db/repl/replication_coordinator_impl_test.cpp
+++ b/src/mongo/db/repl/replication_coordinator_impl_test.cpp
@@ -3559,10 +3559,16 @@ protected:
         return ss.str();
     }
 
-private:
-    virtual void setUp() {
-        ReplCoordTest::setUp();
-        init(ReplSettings());
+    void initReplSetMode() {
+        auto settings = ReplSettings();
+        settings.setReplSetString("replset");
+        init(settings);
+    }
+
+    void initMasterSlaveMode() {
+        auto settings = ReplSettings();
+        settings.setSlave(true);
+        init(settings);
     }
 };
 
@@ -3577,6 +3583,7 @@ TEST_F(StableTimestampTest, CalculateStableTimestamp) {
      * Tests the 'ReplicationCoordinatorImpl::_calculateStableTimestamp' method.
      */
 
+    initReplSetMode();
     auto repl = getReplCoord();
     Timestamp commitPoint;
     boost::optional<Timestamp> expectedStableTimestamp, stableTimestamp;
@@ -3621,6 +3628,7 @@ TEST_F(StableTimestampTest, CleanupStableTimestampCandidates) {
      * Tests the 'ReplicationCoordinatorImpl::_cleanupStableTimestampCandidates' method.
      */
 
+    initReplSetMode();
     auto repl = getReplCoord();
     Timestamp stableTimestamp;
     std::set<Timestamp> timestampCandidates, expectedTimestampCandidates;
@@ -3656,6 +3664,7 @@ TEST_F(StableTimestampTest, SetMyLastAppliedSetsStableTimestampForStorage) {
      * timestamp calculation logic.
      */
 
+    initReplSetMode();
     auto repl = getReplCoord();
     Timestamp stableTimestamp;
 
@@ -3686,6 +3695,7 @@ TEST_F(StableTimestampTest, AdvanceCommitPointSetsStableTimestampForStorage) {
      * calculation logic.
      */
 
+    initReplSetMode();
     auto repl = getReplCoord();
     Timestamp stableTimestamp;
 
@@ -3709,6 +3719,25 @@ TEST_F(StableTimestampTest, AdvanceCommitPointSetsStableTimestampForStorage) {
     ASSERT_TIMESTAMP_SET_EQ(expectedTimestampCandidates, timestampCandidates);
 }
 
+TEST_F(StableTimestampTest, SetMyLastAppliedDoesntAddTimestampCandidateInMasterSlaveMode) {
+
+    /**
+     * Test that 'setMyLastAppliedOpTime' doesn't add timestamp candidates to the stable timestamp
+     * list when running in master-slave mode.
+     */
+
+    initMasterSlaveMode();
+    auto repl = getReplCoord();
+    Timestamp stableTimestamp;
+
+    ASSERT(repl->getStableTimestampCandidates_forTest().empty());
+
+    repl->setMyLastAppliedOpTime(OpTime({0, 1}, 0));
+    repl->setMyLastAppliedOpTime(OpTime({0, 2}, 0));
+
+    // Make sure no timestamps candidates were added.
+    ASSERT(repl->getStableTimestampCandidates_forTest().empty());
+}
 
 TEST_F(ReplCoordTest, NodeReturnsShutdownInProgressWhenWaitingUntilAnOpTimeDuringShutdown) {
     assertStartSuccess(BSON("_id"