SERVER-75757 Get rid of `autoSplitOnly` balancing mode

3 files changed, 28 insertions, 14 deletions

diff --git a/src/mongo/s/balancer_configuration.cpp b/src/mongo/s/balancer_configuration.cpp
index 9375fae3338..bf67de9eca8 100644
--- a/src/mongo/s/balancer_configuration.cpp
+++ b/src/mongo/s/balancer_configuration.cpp
@@ -83,8 +83,7 @@ const char kAttemptToBalanceJumboChunks[] = "attemptToBalanceJumboChunks";
 }  // namespace
 
 const char BalancerSettingsType::kKey[] = "balancer";
-// TODO SERVER-75757: get rid of legacy `autoSplitOnly` mode
-const char* BalancerSettingsType::kBalancerModes[] = {"full", "autoSplitOnly", "off"};
+const char* BalancerSettingsType::kBalancerModes[] = {"full", "off"};
 
 const char ChunkSizeSettingsType::kKey[] = "chunksize";
 const uint64_t ChunkSizeSettingsType::kDefaultMaxChunkSizeBytes{128 * 1024 * 1024};
@@ -306,10 +305,22 @@ StatusWith<BalancerSettingsType> BalancerSettingsType::fromBSON(const BSONObj& o
                 return status;
             auto it = std::find(std::begin(kBalancerModes), std::end(kBalancerModes), modeStr);
             if (it == std::end(kBalancerModes)) {
-                return Status(ErrorCodes::BadValue, "Invalid balancer mode");
+                std::vector<std::string> supportedModes;
+                std::transform(std::begin(kBalancerModes),
+                               std::end(kBalancerModes),
+                               std::back_inserter(supportedModes),
+                               [](const char* supportedMode) -> std::string {
+                                   return std::string(supportedMode);
+                               });
+                LOGV2_WARNING(
+                    7575700,
+                    "Balancer turned off because currently set balancing mode is not valid",
+                    "currentMode"_attr = modeStr,
+                    "supportedModes"_attr = supportedModes);
+                settings._mode = kOff;
+            } else {
+                settings._mode = static_cast<BalancerMode>(it - std::begin(kBalancerModes));
             }
-
-            settings._mode = static_cast<BalancerMode>(it - std::begin(kBalancerModes));
         }
     }
 
diff --git a/src/mongo/s/balancer_configuration.h b/src/mongo/s/balancer_configuration.h
index 2a46669956d..1b104d52b4d 100644
--- a/src/mongo/s/balancer_configuration.h
+++ b/src/mongo/s/balancer_configuration.h
@@ -51,7 +51,7 @@ class StatusWith;
  *
  * balancer: {
  *  stopped: <true|false>,
- *  mode: <full|autoSplitOnly|off>,  // Only consulted if "stopped" is missing or
+ *  mode: <full|off>,  // Only consulted if "stopped" is missing or
  * false activeWindow: { start: "<HH:MM>", stop: "<HH:MM>" }
  * }
  */
@@ -59,9 +59,8 @@ class BalancerSettingsType {
 public:
     // Supported balancer modes
     enum BalancerMode {
-        kFull,           // Balancer will always try to keep the cluster even
-        kAutoSplitOnly,  // Only balance on auto splits
-        kOff,            // Balancer is completely off
+        kFull,  // Balancer will always try to keep the cluster even
+        kOff,   // Balancer is completely off
     };
 
     // The key under which this setting is stored on the config server
diff --git a/src/mongo/s/balancer_configuration_test.cpp b/src/mongo/s/balancer_configuration_test.cpp
index d06d8ba4897..4e97dd3d3ba 100644
--- a/src/mongo/s/balancer_configuration_test.cpp
+++ b/src/mongo/s/balancer_configuration_test.cpp
@@ -184,11 +184,15 @@ TEST(BalancerSettingsType, AllValidBalancerModeOptions) {
 }
 
 TEST(BalancerSettingsType, InvalidBalancerModeOption) {
-    ASSERT_EQ(ErrorCodes::BadValue,
-              BalancerSettingsType::fromBSON(BSON("mode"
-                                                  << "BAD"))
-                  .getStatus()
-                  .code());
+    startCapturingLogMessages();
+    ASSERT_EQ(BalancerSettingsType::kOff,
+              assertGet(BalancerSettingsType::fromBSON(BSON("mode"
+                                                            << "BAD")))
+                  .getMode());
+    stopCapturingLogMessages();
+    ASSERT_EQ(1,
+              countTextFormatLogLinesContaining(
+                  "Balancer turned off because currently set balancing mode is not valid"));
 }
 
 TEST(BalancerSettingsType, BalancingWindowStartLessThanStop) {