SERVER-45438 Create serverStatus section for hedging metrics

5 files changed, 236 insertions, 0 deletions

diff --git a/jstests/sharding/hedging_metrics_server_status.js b/jstests/sharding/hedging_metrics_server_status.js
new file mode 100644
index 00000000000..7010316f6d4
--- /dev/null
+++ b/jstests/sharding/hedging_metrics_server_status.js
@@ -0,0 +1,64 @@
+/*
+ * Tests hedging metrics in the serverStatus output.
+ * @tags: [requires_fcv_44]
+ */
+(function() {
+"use strict";
+
+/*
+ * Verifies that the server status response has the hegingMetrics fields that we expect.
+ */
+function verifyServerStatusFields(serverStatusResponse) {
+    assert(serverStatusResponse.hasOwnProperty("hedgingMetrics"),
+           "Expected the serverStatus response to have a 'hedgingMetrics' field\n" +
+               tojson(serverStatusResponse));
+    assert(
+        serverStatusResponse.hedgingMetrics.hasOwnProperty("numTotalOperations"),
+        "The 'hedgingMetrics' field in serverStatus did not have the 'numTotalOperations' field\n" +
+            tojson(serverStatusResponse.hedgingMetrics));
+    assert(
+        serverStatusResponse.hedgingMetrics.hasOwnProperty("numTotalHedgedOperations"),
+        "The 'hedgingMetrics' field in serverStatus did not have the 'numTotalHedgedOperations' field\n" +
+            tojson(serverStatusResponse.hedgingMetrics));
+    assert(
+        serverStatusResponse.hedgingMetrics.hasOwnProperty("numAdvantageouslyHedgedOperations"),
+        "The 'hedgingMetrics' field in serverStatus did not have the 'numAdvantageouslyHedgedOperations' field\n" +
+            tojson(serverStatusResponse.hedgingMetrics));
+}
+
+/*
+ * Verifies that the hedgingMetrics in the server status response is equal to the expected
+ * hedgingMetrics.
+ */
+function checkServerStatusHedgingMetrics(mongosConn, expectedHedgingMetrics) {
+    const serverStatus = assert.commandWorked(mongosConn.adminCommand({serverStatus: 1}));
+    verifyServerStatusFields(serverStatus);
+
+    assert.eq(expectedHedgingMetrics.numTotalOperations,
+              serverStatus.hedgingMetrics.numTotalOperations);
+    assert.eq(expectedHedgingMetrics.numTotalHedgedOperations,
+              serverStatus.hedgingMetrics.numTotalHedgedOperations);
+}
+
+const st = new ShardingTest({shards: 2});
+const dbName = "foo";
+const collName = "bar";
+const ns = dbName + "." + collName;
+const testDB = st.s.getDB(dbName);
+
+assert.commandWorked(st.s.adminCommand({enableSharding: dbName}));
+st.ensurePrimaryShard(dbName, st.shard0.shardName);
+assert.commandWorked(st.s.adminCommand({shardCollection: ns, key: {x: 1}}));
+
+let expectedHedgingMetrics = {numTotalOperations: 0, numTotalHedgedOperations: 0};
+
+assert.commandWorked(
+    testDB.runCommand({query: {find: collName}, $readPreference: {mode: "primary"}}));
+checkServerStatusHedgingMetrics(testDB, expectedHedgingMetrics);
+
+assert.commandWorked(
+    testDB.runCommand({query: {find: collName}, $readPreference: {mode: "nearest", hedge: {}}}));
+checkServerStatusHedgingMetrics(testDB, expectedHedgingMetrics);
+
+st.stop();
+}());
diff --git a/src/mongo/s/client/SConscript b/src/mongo/s/client/SConscript
index e11419eb79f..126545f850c 100644
--- a/src/mongo/s/client/SConscript
+++ b/src/mongo/s/client/SConscript
@@ -8,6 +8,7 @@ env.Library(
     target='sharding_client',
     source=[
         'shard_remote.cpp',
+        'hedging_metrics.cpp',
         'num_hosts_targeted_metrics.cpp',
          env.Idlc('shard_remote.idl')[0],
     ],
diff --git a/src/mongo/s/client/hedging_metrics.cpp b/src/mongo/s/client/hedging_metrics.cpp
new file mode 100644
index 00000000000..227e8a98e12
--- /dev/null
+++ b/src/mongo/s/client/hedging_metrics.cpp
@@ -0,0 +1,80 @@
+/**
+ *    Copyright (C) 2020-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/s/client/hedging_metrics.h"
+
+namespace mongo {
+
+namespace {
+const auto HedgingMetricsDecoration = ServiceContext::declareDecoration<HedgingMetrics>();
+}  // namespace
+
+HedgingMetrics* HedgingMetrics::get(ServiceContext* service) {
+    return &HedgingMetricsDecoration(service);
+}
+
+HedgingMetrics* HedgingMetrics::get(OperationContext* opCtx) {
+    return get(opCtx->getServiceContext());
+}
+
+long long HedgingMetrics::getNumTotalOperations() const {
+    return _numTotalOperations.load();
+}
+
+void HedgingMetrics::incrementNumTotalOperations() {
+    _numTotalOperations.fetchAndAdd(1);
+}
+
+long long HedgingMetrics::getNumTotalHedgedOperations() const {
+    return _numTotalHedgedOperations.load();
+}
+
+void HedgingMetrics::incrementNumTotalHedgedOperations() {
+    _numTotalHedgedOperations.fetchAndAdd(1);
+}
+
+long long HedgingMetrics::getNumAdvantageouslyHedgedOperations() const {
+    return _numAdvantageouslyHedgedOperations.load();
+}
+
+void HedgingMetrics::incrementNumAdvantageouslyHedgedOperations() {
+    _numAdvantageouslyHedgedOperations.fetchAndAdd(1);
+}
+
+BSONObj HedgingMetrics::toBSON() const {
+    BSONObjBuilder builder;
+
+    builder.append("numTotalOperations", _numTotalOperations.load());
+    builder.append("numTotalHedgedOperations", _numTotalHedgedOperations.load());
+    builder.append("numAdvantageouslyHedgedOperations", _numAdvantageouslyHedgedOperations.load());
+
+    return builder.obj();
+}
+
+}  // namespace mongo
diff --git a/src/mongo/s/client/hedging_metrics.h b/src/mongo/s/client/hedging_metrics.h
new file mode 100644
index 00000000000..fae226f342a
--- /dev/null
+++ b/src/mongo/s/client/hedging_metrics.h
@@ -0,0 +1,73 @@
+/**
+ *    Copyright (C) 2020-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/service_context.h"
+
+namespace mongo {
+
+/**
+ * Container for server-wide hedging metrics.
+ */
+class HedgingMetrics {
+    HedgingMetrics(const HedgingMetrics&) = delete;
+    HedgingMetrics& operator=(const HedgingMetrics&) = delete;
+
+public:
+    HedgingMetrics() = default;
+
+    static HedgingMetrics* get(ServiceContext* service);
+    static HedgingMetrics* get(OperationContext* opCtx);
+
+    long long getNumTotalOperations() const;
+    void incrementNumTotalOperations();
+
+    long long getNumTotalHedgedOperations() const;
+    void incrementNumTotalHedgedOperations();
+
+    long long getNumAdvantageouslyHedgedOperations() const;
+    void incrementNumAdvantageouslyHedgedOperations();
+
+    BSONObj toBSON() const;
+
+private:
+    // The number of all operations with readPreference options such that they could be hedged.
+    AtomicWord<long long> _numTotalOperations{0};
+
+    // The number of all operations that actually dispatched an additional rpc.
+    AtomicWord<long long> _numTotalHedgedOperations{0};
+
+    // The number of all operations where a rpc other than the first one fulfilled the client
+    // request.
+    AtomicWord<long long> _numAdvantageouslyHedgedOperations{0};
+};
+
+}  // namespace mongo
diff --git a/src/mongo/s/s_sharding_server_status.cpp b/src/mongo/s/s_sharding_server_status.cpp
index 0bb94bc5775..6029439d28d 100644
--- a/src/mongo/s/s_sharding_server_status.cpp
+++ b/src/mongo/s/s_sharding_server_status.cpp
@@ -33,6 +33,7 @@
 #include "mongo/db/commands/server_status.h"
 #include "mongo/s/balancer_configuration.h"
 #include "mongo/s/catalog_cache.h"
+#include "mongo/s/client/hedging_metrics.h"
 #include "mongo/s/client/num_hosts_targeted_metrics.h"
 #include "mongo/s/client/shard_registry.h"
 #include "mongo/s/grid.h"
@@ -92,5 +93,22 @@ public:
 
 } shardingStatisticsServerStatus;
 
+class HedgingMetricsServerStatus : public ServerStatusSection {
+public:
+    HedgingMetricsServerStatus() : ServerStatusSection("hedgingMetrics") {}
+
+    ~HedgingMetricsServerStatus() override = default;
+
+    bool includeByDefault() const override {
+        return true;
+    }
+
+    BSONObj generateSection(OperationContext* opCtx,
+                            const BSONElement& configElement) const override {
+        return HedgingMetrics::get(opCtx)->toBSON();
+    }
+
+} hedgingMetricsServerStatus;
+
 }  // namespace
 }  // namespace mongo