SERVER-38998 Create serverStatus metrics for readConcern

src/mongo/db/SConscript

@@ -682,6 +682,7 @@ env.Library(
     source=[
         'catalog_raii.cpp',
         'retryable_writes_stats.cpp',
+        'server_read_concern_metrics.cpp',
         'server_transactions_metrics.cpp',
         'session_catalog_mongod.cpp',
         'single_transaction_stats.cpp',
@@ -691,6 +692,7 @@ env.Library(
         'transaction_participant.cpp',
         's/recover_transaction_decision_from_local_participant.cpp',
         env.Idlc('session_txn_record.idl')[0],
+        env.Idlc('read_concern_stats.idl')[0],
         env.Idlc('transactions_stats.idl')[0],
     ],
     LIBDEPS=[

src/mongo/db/commands/find_cmd.cpp

@@ -49,6 +49,7 @@
 #include "mongo/db/repl/replication_coordinator.h"
 #include "mongo/db/s/collection_sharding_state.h"
 #include "mongo/db/server_parameters.h"
+#include "mongo/db/server_read_concern_metrics.h"
 #include "mongo/db/service_context.h"
 #include "mongo/db/stats/counters.h"
 #include "mongo/db/transaction_participant.h"
@@ -227,6 +228,8 @@ class FindCmd final : public Command {
         void run(OperationContext* opCtx, rpc::ReplyBuilderInterface* result) {
             // Although it is a command, a find command gets counted as a query.
             globalOpCounters.gotQuery();
+            ServerReadConcernMetrics::get(opCtx)->recordReadConcern(
+                repl::ReadConcernArgs::get(opCtx));
 
             // Parse the command BSON to a QueryRequest.
             const bool isExplain = false;

src/mongo/db/read_concern_stats.idl

@@ -0,0 +1,63 @@
+# Copyright (C) 2018-present MongoDB, Inc.
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the Server Side Public License, version 1,
+# as published by MongoDB, Inc.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# Server Side Public License for more details.
+#
+# You should have received a copy of the Server Side Public License
+# along with this program. If not, see
+# <http://www.mongodb.com/licensing/server-side-public-license>.
+#
+# As a special exception, the copyright holders give permission to link the
+# code of portions of this program with the OpenSSL library under certain
+# conditions as described in each individual source file and distribute
+# linked combinations including the program with the OpenSSL library. You
+# must comply with the Server Side Public License in all respects for
+# all of the code used other than as permitted herein. If you modify file(s)
+# with this exception, you may extend this exception to your version of the
+# file(s), but you are not obligated to do so. If you do not wish to do so,
+# delete this exception statement from your version. If you delete this
+# exception statement from all source files in the program, then also delete
+# it in the license file.
+#
+
+# This IDL file describes the BSON format for ReadConcernStats, and
+# handles the serialization to and deserialization from its BSON representation
+# for that class.
+
+global:
+  cpp_namespace: "mongo"
+
+imports:
+  - "mongo/idl/basic_types.idl"
+
+structs:
+
+  ReadConcernStats:
+    description: "A struct representing the section of the server status
+                  command with information about readConcern levels used by operations"
+    strict: true
+    fields:
+      available:
+        type: long
+        default: 0
+      linearizable:
+        type: long
+        default: 0
+      local:
+        type: long
+        default: 0
+      majority:
+        type: long
+        default: 0
+      snapshot:
+        type: long
+        default: 0
+      none:
+        type: long
+        default: 0

src/mongo/db/repl/read_concern_args.cpp

@@ -114,6 +114,10 @@ bool ReadConcernArgs::hasLevel() const {
     return _level.is_initialized();
 }
 
+bool ReadConcernArgs::hasOriginalLevel() const {
+    return _originalLevel.is_initialized();
+}
+
 boost::optional<OpTime> ReadConcernArgs::getArgsOpTime() const {
     return _opTime;
 }
@@ -194,6 +198,7 @@ Status ReadConcernArgs::initialize(const BSONElement& readConcernElem) {
                                             << " must be either 'local', 'majority', "
                                                "'linearizable', 'available', or 'snapshot'");
             }
+            _originalLevel = _level;
         } else {
             return Status(ErrorCodes::InvalidOptions,
                           str::stream() << "Unrecognized option in " << kReadConcernFieldName
@@ -293,7 +298,7 @@ Status ReadConcernArgs::upconvertReadConcernLevelToSnapshot() {
                                     << "' is provided");
     }
 
-    _originalLevel = _level ? *_level : ReadConcernLevel::kLocalReadConcern;
+    _originalLevel = _level;
     _level = ReadConcernLevel::kSnapshotReadConcern;
     return Status::OK();
 }

src/mongo/db/repl/read_concern_args.h

@@ -154,6 +154,11 @@ class ReadConcernArgs {
      */
     bool hasLevel() const;
 
+    /**
+     * Checks whether _originalLevel is explicitly set.
+     */
+    bool hasOriginalLevel() const;
+
     /**
      * Returns the opTime. Deprecated: will be replaced with getArgsAfterClusterTime.
      */

src/mongo/db/server_read_concern_metrics.cpp

@@ -0,0 +1,116 @@
+/**
+ *    Copyright (C) 2018-present MongoDB, Inc.
+ *
+ *    This program is free software: you can redistribute it and/or modify
+ *    it under the terms of the Server Side Public License, version 1,
+ *    as published by MongoDB, Inc.
+ *
+ *    This program is distributed in the hope that it will be useful,
+ *    but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *    Server Side Public License for more details.
+ *
+ *    You should have received a copy of the Server Side Public License
+ *    along with this program. If not, see
+ *    <http://www.mongodb.com/licensing/server-side-public-license>.
+ *
+ *    As a special exception, the copyright holders give permission to link the
+ *    code of portions of this program with the OpenSSL library under certain
+ *    conditions as described in each individual source file and distribute
+ *    linked combinations including the program with the OpenSSL library. You
+ *    must comply with the Server Side Public License in all respects for
+ *    all of the code used other than as permitted herein. If you modify file(s)
+ *    with this exception, you may extend this exception to your version of the
+ *    file(s), but you are not obligated to do so. If you do not wish to do so,
+ *    delete this exception statement from your version. If you delete this
+ *    exception statement from all source files in the program, then also delete
+ *    it in the license file.
+ */
+
+#include "mongo/platform/basic.h"
+
+#include "mongo/db/server_read_concern_metrics.h"
+
+#include "mongo/db/commands/server_status.h"
+#include "mongo/db/jsobj.h"
+#include "mongo/db/operation_context.h"
+#include "mongo/db/read_concern_stats_gen.h"
+#include "mongo/db/service_context.h"
+
+namespace mongo {
+namespace {
+const auto ServerReadConcernMetricsDecoration =
+    ServiceContext::declareDecoration<ServerReadConcernMetrics>();
+}  // namespace
+
+ServerReadConcernMetrics* ServerReadConcernMetrics::get(ServiceContext* service) {
+    return &ServerReadConcernMetricsDecoration(service);
+}
+
+ServerReadConcernMetrics* ServerReadConcernMetrics::get(OperationContext* opCtx) {
+    return get(opCtx->getServiceContext());
+}
+
+void ServerReadConcernMetrics::recordReadConcern(const repl::ReadConcernArgs& readConcernArgs) {
+    if (!readConcernArgs.hasOriginalLevel()) {
+        _noLevelCount.fetchAndAdd(1);
+        return;
+    }
+
+    switch (readConcernArgs.getOriginalLevel()) {
+        case repl::ReadConcernLevel::kAvailableReadConcern:
+            _levelAvailableCount.fetchAndAdd(1);
+            break;
+
+        case repl::ReadConcernLevel::kLinearizableReadConcern:
+            _levelLinearizableCount.fetchAndAdd(1);
+            break;
+
+        case repl::ReadConcernLevel::kLocalReadConcern:
+            _levelLocalCount.fetchAndAdd(1);
+            break;
+
+        case repl::ReadConcernLevel::kMajorityReadConcern:
+            _levelMajorityCount.fetchAndAdd(1);
+            break;
+
+        case repl::ReadConcernLevel::kSnapshotReadConcern:
+            _levelSnapshotCount.fetchAndAdd(1);
+            break;
+
+        default:
+            MONGO_UNREACHABLE;
+    }
+}
+
+void ServerReadConcernMetrics::updateStats(ReadConcernStats* stats, OperationContext* opCtx) {
+    stats->setAvailable(_levelAvailableCount.load());
+    stats->setLinearizable(_levelLinearizableCount.load());
+    stats->setLocal(_levelLocalCount.load());
+    stats->setMajority(_levelMajorityCount.load());
+    stats->setSnapshot(_levelSnapshotCount.load());
+    stats->setNone(_noLevelCount.load());
+}
+
+namespace {
+class OpReadConcernCountersSSS : public ServerStatusSection {
+public:
+    OpReadConcernCountersSSS() : ServerStatusSection("opReadConcernCounters") {}
+
+    ~OpReadConcernCountersSSS() override = default;
+
+    bool includeByDefault() const override {
+        return true;
+    }
+
+    BSONObj generateSection(OperationContext* opCtx,
+                            const BSONElement& configElement) const override {
+        ReadConcernStats stats;
+        ServerReadConcernMetrics::get(opCtx)->updateStats(&stats, opCtx);
+        return stats.toBSON();
+    }
+
+} opReadConcernCountersSSS;
+}  // namespace
+
+}  // namespace mongo

src/mongo/db/server_read_concern_metrics.h

@@ -0,0 +1,71 @@
+
+/**
+ *    Copyright (C) 2018-present MongoDB, Inc.
+ *
+ *    This program is free software: you can redistribute it and/or modify
+ *    it under the terms of the Server Side Public License, version 1,
+ *    as published by MongoDB, Inc.
+ *
+ *    This program is distributed in the hope that it will be useful,
+ *    but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *    Server Side Public License for more details.
+ *
+ *    You should have received a copy of the Server Side Public License
+ *    along with this program. If not, see
+ *    <http://www.mongodb.com/licensing/server-side-public-license>.
+ *
+ *    As a special exception, the copyright holders give permission to link the
+ *    code of portions of this program with the OpenSSL library under certain
+ *    conditions as described in each individual source file and distribute
+ *    linked combinations including the program with the OpenSSL library. You
+ *    must comply with the Server Side Public License in all respects for
+ *    all of the code used other than as permitted herein. If you modify file(s)
+ *    with this exception, you may extend this exception to your version of the
+ *    file(s), but you are not obligated to do so. If you do not wish to do so,
+ *    delete this exception statement from your version. If you delete this
+ *    exception statement from all source files in the program, then also delete
+ *    it in the license file.
+ */
+
+#pragma once
+
+#include "mongo/db/operation_context.h"
+#include "mongo/db/read_concern_stats_gen.h"
+#include "mongo/db/repl/read_concern_args.h"
+#include "mongo/db/service_context.h"
+
+namespace mongo {
+
+/**
+ * Container for server-wide statistics on readConcern levels used by operations.
+ */
+class ServerReadConcernMetrics {
+    MONGO_DISALLOW_COPYING(ServerReadConcernMetrics);
+
+public:
+    ServerReadConcernMetrics() = default;
+
+    static ServerReadConcernMetrics* get(ServiceContext* service);
+    static ServerReadConcernMetrics* get(OperationContext* opCtx);
+
+    /**
+     * Updates counter for the level of 'readConcernArgs'.
+     */
+    void recordReadConcern(const repl::ReadConcernArgs& readConcernArgs);
+
+    /**
+     * Appends the accumulated stats to a readConcern stats object.
+     */
+    void updateStats(ReadConcernStats* stats, OperationContext* opCtx);
+
+private:
+    AtomicWord<unsigned long long> _levelAvailableCount{0};
+    AtomicWord<unsigned long long> _levelLinearizableCount{0};
+    AtomicWord<unsigned long long> _levelLocalCount{0};
+    AtomicWord<unsigned long long> _levelMajorityCount{0};
+    AtomicWord<unsigned long long> _levelSnapshotCount{0};
+    AtomicWord<unsigned long long> _noLevelCount{0};
+};
+
+}  // namespace mongo

src/mongo/db/service_entry_point_common.cpp

@@ -69,6 +69,7 @@
 #include "mongo/db/s/operation_sharding_state.h"
 #include "mongo/db/s/sharded_connection_info.h"
 #include "mongo/db/s/sharding_state.h"
+#include "mongo/db/server_read_concern_metrics.h"
 #include "mongo/db/service_entry_point_common.h"
 #include "mongo/db/session_catalog_mongod.h"
 #include "mongo/db/snapshot_window_util.h"
@@ -952,6 +953,7 @@ DbResponse receivedQuery(OperationContext* opCtx,
                          const ServiceEntryPointCommon::Hooks& behaviors) {
     invariant(!nss.isCommand());
     globalOpCounters.gotQuery();
+    ServerReadConcernMetrics::get(opCtx)->recordReadConcern(repl::ReadConcernArgs::get(opCtx));
 
     DbMessage d(m);
     QueryMessage q(d);