SERVER-39267 Guard opWriteConcernCounters behind flagr4.0.6-rc1r4.0.6

(cherry picked from commit 941c4fbab21029e3bbe577d953250116cd0e8533)

3 files changed, 50 insertions, 14 deletions

diff --git a/jstests/noPassthrough/server_write_concern_metrics.js b/jstests/noPassthrough/server_write_concern_metrics.js
index 83ab7e8dd38..e7c15f38490 100644
--- a/jstests/noPassthrough/server_write_concern_metrics.js
+++ b/jstests/noPassthrough/server_write_concern_metrics.js
@@ -68,7 +68,8 @@
                       tojson(newStats));
     }
 
-    const rst = new ReplSetTest({nodes: 2});
+    const rst = new ReplSetTest(
+        {nodes: 2, nodeOptions: {setParameter: 'reportOpWriteConcernCountersInServerStatus=true'}});
     rst.startSet();
     let config = rst.getReplSetConfig();
     config.members[1].priority = 0;
diff --git a/src/mongo/db/stats/server_write_concern_metrics.cpp b/src/mongo/db/stats/server_write_concern_metrics.cpp
index 3bcf1fe99af..da8e74c9011 100644
--- a/src/mongo/db/stats/server_write_concern_metrics.cpp
+++ b/src/mongo/db/stats/server_write_concern_metrics.cpp
@@ -34,9 +34,16 @@
 #include "mongo/db/commands/server_status.h"
 #include "mongo/db/jsobj.h"
 #include "mongo/db/operation_context.h"
+#include "mongo/db/server_parameters.h"
 #include "mongo/db/service_context.h"
 
 namespace mongo {
+
+// opWriteConcernCounters are not tracked unless 'reportOpWriteConcernCountersInServerStatus' is
+// true. This is false by default because the mutex acquisition impacts performance when SSL is
+// disabled. (When SSL is enabled, other mutexes dominate.)
+MONGO_EXPORT_STARTUP_SERVER_PARAMETER(reportOpWriteConcernCountersInServerStatus, bool, false);
+
 namespace {
 const auto ServerWriteConcernMetricsDecoration =
     ServiceContext::declareDecoration<ServerWriteConcernMetrics>();
@@ -50,7 +57,41 @@ ServerWriteConcernMetrics* ServerWriteConcernMetrics::get(OperationContext* opCt
     return get(opCtx->getServiceContext());
 }
 
+void ServerWriteConcernMetrics::recordWriteConcernForInserts(
+    const WriteConcernOptions& writeConcernOptions, size_t numInserts) {
+    if (!reportOpWriteConcernCountersInServerStatus) {
+        return;
+    }
+
+    stdx::lock_guard<stdx::mutex> lg(_mutex);
+    _insertMetrics.recordWriteConcern(writeConcernOptions, numInserts);
+}
+
+void ServerWriteConcernMetrics::recordWriteConcernForUpdate(
+    const WriteConcernOptions& writeConcernOptions) {
+    if (!reportOpWriteConcernCountersInServerStatus) {
+        return;
+    }
+
+    stdx::lock_guard<stdx::mutex> lg(_mutex);
+    _updateMetrics.recordWriteConcern(writeConcernOptions);
+}
+
+void ServerWriteConcernMetrics::recordWriteConcernForDelete(
+    const WriteConcernOptions& writeConcernOptions) {
+    if (!reportOpWriteConcernCountersInServerStatus) {
+        return;
+    }
+
+    stdx::lock_guard<stdx::mutex> lg(_mutex);
+    _deleteMetrics.recordWriteConcern(writeConcernOptions);
+}
+
 BSONObj ServerWriteConcernMetrics::toBSON() const {
+    if (!reportOpWriteConcernCountersInServerStatus) {
+        return BSONObj();
+    }
+
     stdx::lock_guard<stdx::mutex> lg(_mutex);
 
     BSONObjBuilder builder;
@@ -117,7 +158,10 @@ public:
     ~OpWriteConcernCountersSSS() override = default;
 
     bool includeByDefault() const override {
-        return true;
+        // When 'reportOpWriteConcernCountersInServerStatus' is false, do not include this section
+        // unless requested by the user. Even if the user requests the section, it will not be
+        // included because an empty BSONObj is generated for the section.
+        return reportOpWriteConcernCountersInServerStatus;
     }
 
     BSONObj generateSection(OperationContext* opCtx,
diff --git a/src/mongo/db/stats/server_write_concern_metrics.h b/src/mongo/db/stats/server_write_concern_metrics.h
index c7a17dcc5d7..9a9525d1b30 100644
--- a/src/mongo/db/stats/server_write_concern_metrics.h
+++ b/src/mongo/db/stats/server_write_concern_metrics.h
@@ -53,10 +53,7 @@ public:
      * 'writeConcernOptions'.
      */
     void recordWriteConcernForInserts(const WriteConcernOptions& writeConcernOptions,
-                                      size_t numInserts) {
-        stdx::lock_guard<stdx::mutex> lg(_mutex);
-        _insertMetrics.recordWriteConcern(writeConcernOptions, numInserts);
-    }
+                                      size_t numInserts);
 
     /**
      * Updates the insert metrics according to the 'w' value of 'writeConcernOptions'.
@@ -68,18 +65,12 @@ public:
     /**
      * Updates the update metrics according to the 'w' value of 'writeConcernOptions'.
      */
-    void recordWriteConcernForUpdate(const WriteConcernOptions& writeConcernOptions) {
-        stdx::lock_guard<stdx::mutex> lg(_mutex);
-        _updateMetrics.recordWriteConcern(writeConcernOptions);
-    }
+    void recordWriteConcernForUpdate(const WriteConcernOptions& writeConcernOptions);
 
     /**
      * Updates the delete metrics according to the 'w' value of 'writeConcernOptions'.
      */
-    void recordWriteConcernForDelete(const WriteConcernOptions& writeConcernOptions) {
-        stdx::lock_guard<stdx::mutex> lg(_mutex);
-        _deleteMetrics.recordWriteConcern(writeConcernOptions);
-    }
+    void recordWriteConcernForDelete(const WriteConcernOptions& writeConcernOptions);
 
     BSONObj toBSON() const;