SERVER-47454: Stop re-evaluting sync source if max num changes was exceeded

3 files changed, 63 insertions, 7 deletions

diff --git a/src/mongo/db/repl/topology_coordinator.cpp b/src/mongo/db/repl/topology_coordinator.cpp
index bbe49703822..5159d57b1f7 100644
--- a/src/mongo/db/repl/topology_coordinator.cpp
+++ b/src/mongo/db/repl/topology_coordinator.cpp
@@ -3033,12 +3033,11 @@ bool TopologyCoordinator::shouldChangeSyncSource(const HostAndPort& currentSourc
     return false;
 }
 
-bool TopologyCoordinator::shouldChangeSyncSourceDueToPingTime(
-    const HostAndPort& currentSource,
-    const MemberState& memberState,
-    const OpTime& lastOpTimeFetched,
-    Date_t now,
-    const ReadPreference readPreference) const {
+bool TopologyCoordinator::shouldChangeSyncSourceDueToPingTime(const HostAndPort& currentSource,
+                                                              const MemberState& memberState,
+                                                              const OpTime& lastOpTimeFetched,
+                                                              Date_t now,
+                                                              const ReadPreference readPreference) {
     // If the ping time for currentSource is longer than 'changeSyncSourceThresholdMillis' and we
     // find an eligible sync source that has a ping time shorter than
     // 'changeSyncSourceThresholdMillis', return true.
@@ -3054,6 +3053,12 @@ bool TopologyCoordinator::shouldChangeSyncSourceDueToPingTime(
         return false;
     }
 
+    // If we have already changed sync sources more than 'maxNumSyncSourceChangesPerHour' in the
+    // past hour, do not re-evaluate our sync source.
+    if (_recentSyncSourceChanges.changedTooOftenRecently(now)) {
+        return false;
+    }
+
     const bool primaryOnly = (readPreference == ReadPreference::PrimaryOnly);
     const bool primaryPreferredAndAlreadySyncing =
         (readPreference == ReadPreference::PrimaryPreferred &&
diff --git a/src/mongo/db/repl/topology_coordinator.h b/src/mongo/db/repl/topology_coordinator.h
index 56ec2fd881b..87aacd5aa12 100644
--- a/src/mongo/db/repl/topology_coordinator.h
+++ b/src/mongo/db/repl/topology_coordinator.h
@@ -279,7 +279,7 @@ public:
                                              const MemberState& memberState,
                                              const OpTime& lastOpTimeFetched,
                                              Date_t now,
-                                             const ReadPreference readPreference) const;
+                                             const ReadPreference readPreference);
 
     /**
      * Sets the reported mode of this node to one of RS_SECONDARY, RS_STARTUP2, RS_ROLLBACK or
diff --git a/src/mongo/db/repl/topology_coordinator_v1_test.cpp b/src/mongo/db/repl/topology_coordinator_v1_test.cpp
index 302de461df1..d28062c4fb6 100644
--- a/src/mongo/db/repl/topology_coordinator_v1_test.cpp
+++ b/src/mongo/db/repl/topology_coordinator_v1_test.cpp
@@ -4362,6 +4362,57 @@ TEST_F(ReevalSyncSourceTest, NoChangeWhenNodeNotFoundInConfig) {
                                                                     ReadPreference::Nearest));
 }
 
+TEST_F(ReevalSyncSourceTest, NoChangeWhenChangedTooManyTimesRecently) {
+    getTopoCoord().setPing_forTest(HostAndPort("host2"), pingTimeAboveThreshold);
+    getTopoCoord().setPing_forTest(HostAndPort("host3"), pingTimeBelowThreshold);
+
+    auto recentSyncSourceChanges = getTopoCoord().getRecentSyncSourceChanges_forTest();
+
+    auto first = Date_t::now();
+    recentSyncSourceChanges->addNewEntry(first);
+
+    auto second = Date_t::now();
+    recentSyncSourceChanges->addNewEntry(second);
+
+    auto third = Date_t::now();
+    recentSyncSourceChanges->addNewEntry(third);
+
+    assertTimesEqual({first, second, third}, recentSyncSourceChanges->getChanges_forTest());
+    ASSERT_TRUE(recentSyncSourceChanges->changedTooOftenRecently(now()));
+
+    // We should not change sync sources because we have already changed sync sources more than
+    // 'maxNumSyncSourceChangesPerHour' in the past hour.
+    ASSERT_FALSE(getTopoCoord().shouldChangeSyncSourceDueToPingTime(HostAndPort("host2"),
+                                                                    MemberState::RS_SECONDARY,
+                                                                    lastOpTimeFetched,
+                                                                    now(),
+                                                                    ReadPreference::Nearest));
+}
+
+TEST_F(ReevalSyncSourceTest, ChangeWhenHaveNotChangedTooManyTimesRecently) {
+    getTopoCoord().setPing_forTest(HostAndPort("host2"), pingTimeAboveThreshold);
+    getTopoCoord().setPing_forTest(HostAndPort("host3"), pingTimeBelowThreshold);
+
+    auto recentSyncSourceChanges = getTopoCoord().getRecentSyncSourceChanges_forTest();
+
+    auto first = Date_t::now();
+    recentSyncSourceChanges->addNewEntry(first);
+
+    auto second = Date_t::now();
+    recentSyncSourceChanges->addNewEntry(second);
+
+    assertTimesEqual({first, second}, recentSyncSourceChanges->getChanges_forTest());
+    ASSERT_FALSE(recentSyncSourceChanges->changedTooOftenRecently(now()));
+
+    // We should allow changing sync sources because we have not yet changed sync sources more times
+    // than 'maxNumSyncSourceChangesPerHour' in the past hour.
+    ASSERT_TRUE(getTopoCoord().shouldChangeSyncSourceDueToPingTime(HostAndPort("host2"),
+                                                                   MemberState::RS_SECONDARY,
+                                                                   lastOpTimeFetched,
+                                                                   now(),
+                                                                   ReadPreference::Nearest));
+}
+
 class HeartbeatResponseReconfigTestV1 : public TopoCoordTest {
 public:
     virtual void setUp() {