SERVER-35428 Added ability to add two OpDebug objects together

17 files changed, 393 insertions, 109 deletions

diff --git a/src/mongo/db/SConscript b/src/mongo/db/SConscript
index 7739779e9cc..527e2ce7af6 100644
--- a/src/mongo/db/SConscript
+++ b/src/mongo/db/SConscript
@@ -213,6 +213,16 @@ env.Library(
     ],
 )
 
+env.CppUnitTest(
+    target='curop_test',
+    source=[
+        'curop_test.cpp',
+    ],
+    LIBDEPS=[
+        'curop',
+    ],
+)
+
 env.Library(
     target='curop_failpoint_helpers',
     source=[
diff --git a/src/mongo/db/catalog/capped_utils.cpp b/src/mongo/db/catalog/capped_utils.cpp
index d89fcfe4177..4801b92ca73 100644
--- a/src/mongo/db/catalog/capped_utils.cpp
+++ b/src/mongo/db/catalog/capped_utils.cpp
@@ -231,7 +231,7 @@ mongo::Status mongo::cloneCollectionAsCapped(OperationContext* opCtx,
             // Go to the next document
             retries = 0;
         } catch (const WriteConflictException&) {
-            CurOp::get(opCtx)->debug().writeConflicts++;
+            CurOp::get(opCtx)->debug().additiveMetrics.incrementWriteConflicts(1);
             retries++;  // logAndBackoff expects this to be 1 on first call.
             WriteConflictException::logAndBackoff(retries, "cloneCollectionAsCapped", fromNss.ns());
 
diff --git a/src/mongo/db/catalog/collection_impl.cpp b/src/mongo/db/catalog/collection_impl.cpp
index de2fe045acc..8ef6a71b469 100644
--- a/src/mongo/db/catalog/collection_impl.cpp
+++ b/src/mongo/db/catalog/collection_impl.cpp
@@ -504,7 +504,7 @@ Status CollectionImpl::_insertDocuments(OperationContext* opCtx,
     int64_t keysInserted;
     status = _indexCatalog.indexRecords(opCtx, bsonRecords, &keysInserted);
     if (opDebug) {
-        opDebug->keysInserted += keysInserted;
+        opDebug->additiveMetrics.incrementKeysInserted(keysInserted);
     }
 
     return status;
@@ -569,7 +569,7 @@ void CollectionImpl::deleteDocument(OperationContext* opCtx,
     int64_t keysDeleted;
     _indexCatalog.unindexRecord(opCtx, doc.value(), loc, noWarn, &keysDeleted);
     if (opDebug) {
-        opDebug->keysDeleted += keysDeleted;
+        opDebug->additiveMetrics.incrementKeysDeleted(keysDeleted);
     }
 
     _recordStore->deleteRecord(opCtx, loc);
@@ -686,8 +686,8 @@ RecordId CollectionImpl::updateDocument(OperationContext* opCtx,
             uassertStatusOK(iam->update(
                 opCtx, *updateTickets.mutableMap()[descriptor], &keysInserted, &keysDeleted));
             if (opDebug) {
-                opDebug->keysInserted += keysInserted;
-                opDebug->keysDeleted += keysDeleted;
+                opDebug->additiveMetrics.incrementKeysInserted(keysInserted);
+                opDebug->additiveMetrics.incrementKeysDeleted(keysDeleted);
             }
         }
     }
@@ -747,9 +747,9 @@ StatusWith<RecordId> CollectionImpl::_updateDocumentWithMove(OperationContext* o
 
     moveCounter.increment();
     if (opDebug) {
-        opDebug->nmoved++;
-        opDebug->keysInserted += keysInserted;
-        opDebug->keysDeleted += keysDeleted;
+        opDebug->additiveMetrics.incrementNmoved(1);
+        opDebug->additiveMetrics.incrementKeysInserted(keysInserted);
+        opDebug->additiveMetrics.incrementKeysDeleted(keysDeleted);
     }
 
     return newLocation;
diff --git a/src/mongo/db/catalog/index_create_impl.cpp b/src/mongo/db/catalog/index_create_impl.cpp
index 7f3c45a2f28..9f34942e4ee 100644
--- a/src/mongo/db/catalog/index_create_impl.cpp
+++ b/src/mongo/db/catalog/index_create_impl.cpp
@@ -424,7 +424,7 @@ Status MultiIndexBlockImpl::insertAllDocumentsInCollection(std::set<RecordId>* d
             n++;
             retries = 0;
         } catch (const WriteConflictException&) {
-            CurOp::get(_opCtx)->debug().writeConflicts++;
+            CurOp::get(_opCtx)->debug().additiveMetrics.incrementWriteConflicts(1);
             retries++;  // logAndBackoff expects this to be 1 on first call.
             WriteConflictException::logAndBackoff(
                 retries, "index creation", _collection->ns().ns());
diff --git a/src/mongo/db/commands/find_and_modify.cpp b/src/mongo/db/commands/find_and_modify.cpp
index c097d9f1ea4..4c70636f928 100644
--- a/src/mongo/db/commands/find_and_modify.cpp
+++ b/src/mongo/db/commands/find_and_modify.cpp
@@ -417,7 +417,7 @@ public:
                 opDebug->setPlanSummaryMetrics(summaryStats);
 
                 // Fill out OpDebug with the number of deleted docs.
-                opDebug->ndeleted = getDeleteStats(exec.get())->docsDeleted;
+                opDebug->additiveMetrics.ndeleted = getDeleteStats(exec.get())->docsDeleted;
 
                 if (curOp->shouldDBProfile()) {
                     BSONObjBuilder execStatsBob;
diff --git a/src/mongo/db/concurrency/d_concurrency_test.cpp b/src/mongo/db/concurrency/d_concurrency_test.cpp
index 145f4f31846..d54f2896c62 100644
--- a/src/mongo/db/concurrency/d_concurrency_test.cpp
+++ b/src/mongo/db/concurrency/d_concurrency_test.cpp
@@ -30,6 +30,7 @@
 
 #include "mongo/platform/basic.h"
 
+#include <boost/optional/optional_io.hpp>
 #include <string>
 #include <vector>
 
@@ -132,14 +133,14 @@ TEST_F(DConcurrencyTestFixture, WriteConflictRetryRetriesFunctionOnWriteConflict
     auto opCtx = makeOperationContext();
     opCtx->swapLockState(stdx::make_unique<MMAPV1LockerImpl>());
     auto&& opDebug = CurOp::get(opCtx.get())->debug();
-    ASSERT_EQUALS(0LL, opDebug.writeConflicts);
+    ASSERT_EQUALS(boost::none, opDebug.additiveMetrics.writeConflicts);
     ASSERT_EQUALS(100, writeConflictRetry(opCtx.get(), "", "", [&opDebug] {
-                      if (opDebug.writeConflicts == 0LL) {
+                      if (!opDebug.additiveMetrics.writeConflicts) {
                           throw WriteConflictException();
                       }
                       return 100;
                   }));
-    ASSERT_EQUALS(1LL, opDebug.writeConflicts);
+    ASSERT_EQUALS(1LL, *opDebug.additiveMetrics.writeConflicts);
 }
 
 TEST_F(DConcurrencyTestFixture, WriteConflictRetryPropagatesNonWriteConflictException) {
diff --git a/src/mongo/db/concurrency/write_conflict_exception.h b/src/mongo/db/concurrency/write_conflict_exception.h
index 7b7e1cc1e9a..193ebfb112e 100644
--- a/src/mongo/db/concurrency/write_conflict_exception.h
+++ b/src/mongo/db/concurrency/write_conflict_exception.h
@@ -90,7 +90,7 @@ auto writeConflictRetry(OperationContext* opCtx, StringData opStr, StringData ns
         try {
             return f();
         } catch (WriteConflictException const&) {
-            ++CurOp::get(opCtx)->debug().writeConflicts;
+            CurOp::get(opCtx)->debug().additiveMetrics.incrementWriteConflicts(1);
             WriteConflictException::logAndBackoff(attempts, opStr, ns);
             ++attempts;
             opCtx->recoveryUnit()->abandonSnapshot();
diff --git a/src/mongo/db/curop.cpp b/src/mongo/db/curop.cpp
index 28091bfd359..08fb567b729 100644
--- a/src/mongo/db/curop.cpp
+++ b/src/mongo/db/curop.cpp
@@ -496,6 +496,9 @@ StringData getProtoString(int op) {
 #define OPDEBUG_TOSTRING_HELP_BOOL(x) \
     if (x)                            \
     s << " " #x ":" << (x)
+#define OPDEBUG_TOSTRING_HELP_OPTIONAL(x, y) \
+    if (y)                                   \
+    s << " " x ":" << (*y)
 
 string OpDebug::report(Client* client,
                        const CurOp& curop,
@@ -553,38 +556,24 @@ string OpDebug::report(Client* client,
     OPDEBUG_TOSTRING_HELP(ntoskip);
     OPDEBUG_TOSTRING_HELP_BOOL(exhaust);
 
-    OPDEBUG_TOSTRING_HELP(keysExamined);
-    OPDEBUG_TOSTRING_HELP(docsExamined);
+    OPDEBUG_TOSTRING_HELP_OPTIONAL("keysExamined", additiveMetrics.keysExamined);
+    OPDEBUG_TOSTRING_HELP_OPTIONAL("docsExamined", additiveMetrics.docsExamined);
     OPDEBUG_TOSTRING_HELP_BOOL(hasSortStage);
     OPDEBUG_TOSTRING_HELP_BOOL(fromMultiPlanner);
     OPDEBUG_TOSTRING_HELP_BOOL(replanned);
-    OPDEBUG_TOSTRING_HELP(nMatched);
-    OPDEBUG_TOSTRING_HELP(nModified);
-    OPDEBUG_TOSTRING_HELP(ninserted);
-    OPDEBUG_TOSTRING_HELP(ndeleted);
+    OPDEBUG_TOSTRING_HELP_OPTIONAL("nMatched", additiveMetrics.nMatched);
+    OPDEBUG_TOSTRING_HELP_OPTIONAL("nModified", additiveMetrics.nModified);
+    OPDEBUG_TOSTRING_HELP_OPTIONAL("ninserted", additiveMetrics.ninserted);
+    OPDEBUG_TOSTRING_HELP_OPTIONAL("ndeleted", additiveMetrics.ndeleted);
     OPDEBUG_TOSTRING_HELP_BOOL(fastmodinsert);
     OPDEBUG_TOSTRING_HELP_BOOL(upsert);
     OPDEBUG_TOSTRING_HELP_BOOL(cursorExhausted);
 
-    if (nmoved > 0) {
-        s << " nmoved:" << nmoved;
-    }
-
-    if (keysInserted > 0) {
-        s << " keysInserted:" << keysInserted;
-    }
-
-    if (keysDeleted > 0) {
-        s << " keysDeleted:" << keysDeleted;
-    }
-
-    if (prepareReadConflicts > 0) {
-        s << " prepareReadConflicts:" << prepareReadConflicts;
-    }
-
-    if (writeConflicts > 0) {
-        s << " writeConflicts:" << writeConflicts;
-    }
+    OPDEBUG_TOSTRING_HELP_OPTIONAL("nmoved", additiveMetrics.nmoved);
+    OPDEBUG_TOSTRING_HELP_OPTIONAL("keysInserted", additiveMetrics.keysInserted);
+    OPDEBUG_TOSTRING_HELP_OPTIONAL("keysDeleted", additiveMetrics.keysDeleted);
+    OPDEBUG_TOSTRING_HELP_OPTIONAL("prepareReadConflicts", additiveMetrics.prepareReadConflicts);
+    OPDEBUG_TOSTRING_HELP_OPTIONAL("writeConflicts", additiveMetrics.writeConflicts);
 
     s << " numYields:" << curop.numYields();
     OPDEBUG_TOSTRING_HELP(nreturned);
@@ -623,6 +612,9 @@ string OpDebug::report(Client* client,
 #define OPDEBUG_APPEND_BOOL(x) \
     if (x)                     \
     b.appendBool(#x, (x))
+#define OPDEBUG_APPEND_OPTIONAL(x, y) \
+    if (y)                            \
+    b.appendNumber(x, (*y))
 
 void OpDebug::append(const CurOp& curop,
                      const SingleThreadedLockStats& lockStats,
@@ -645,38 +637,24 @@ void OpDebug::append(const CurOp& curop,
     OPDEBUG_APPEND_NUMBER(cursorid);
     OPDEBUG_APPEND_BOOL(exhaust);
 
-    OPDEBUG_APPEND_NUMBER(keysExamined);
-    OPDEBUG_APPEND_NUMBER(docsExamined);
+    OPDEBUG_APPEND_OPTIONAL("keysExamined", additiveMetrics.keysExamined);
+    OPDEBUG_APPEND_OPTIONAL("docsExamined", additiveMetrics.docsExamined);
     OPDEBUG_APPEND_BOOL(hasSortStage);
     OPDEBUG_APPEND_BOOL(fromMultiPlanner);
     OPDEBUG_APPEND_BOOL(replanned);
-    OPDEBUG_APPEND_NUMBER(nMatched);
-    OPDEBUG_APPEND_NUMBER(nModified);
-    OPDEBUG_APPEND_NUMBER(ninserted);
-    OPDEBUG_APPEND_NUMBER(ndeleted);
+    OPDEBUG_APPEND_OPTIONAL("nMatched", additiveMetrics.nMatched);
+    OPDEBUG_APPEND_OPTIONAL("nModified", additiveMetrics.nModified);
+    OPDEBUG_APPEND_OPTIONAL("ninserted", additiveMetrics.ninserted);
+    OPDEBUG_APPEND_OPTIONAL("ndeleted", additiveMetrics.ndeleted);
     OPDEBUG_APPEND_BOOL(fastmodinsert);
     OPDEBUG_APPEND_BOOL(upsert);
     OPDEBUG_APPEND_BOOL(cursorExhausted);
 
-    if (nmoved > 0) {
-        b.appendNumber("nmoved", nmoved);
-    }
-
-    if (keysInserted > 0) {
-        b.appendNumber("keysInserted", keysInserted);
-    }
-
-    if (keysDeleted > 0) {
-        b.appendNumber("keysDeleted", keysDeleted);
-    }
-
-    if (prepareReadConflicts > 0) {
-        b.appendNumber("prepareReadConflicts", prepareReadConflicts);
-    }
-
-    if (writeConflicts > 0) {
-        b.appendNumber("writeConflicts", writeConflicts);
-    }
+    OPDEBUG_APPEND_OPTIONAL("nmoved", additiveMetrics.nmoved);
+    OPDEBUG_APPEND_OPTIONAL("keysInserted", additiveMetrics.keysInserted);
+    OPDEBUG_APPEND_OPTIONAL("keysDeleted", additiveMetrics.keysDeleted);
+    OPDEBUG_APPEND_OPTIONAL("prepareReadConflicts", additiveMetrics.prepareReadConflicts);
+    OPDEBUG_APPEND_OPTIONAL("writeConflicts", additiveMetrics.writeConflicts);
 
     b.appendNumber("numYield", curop.numYields());
     OPDEBUG_APPEND_NUMBER(nreturned);
@@ -711,11 +689,84 @@ void OpDebug::append(const CurOp& curop,
 }
 
 void OpDebug::setPlanSummaryMetrics(const PlanSummaryStats& planSummaryStats) {
-    keysExamined = planSummaryStats.totalKeysExamined;
-    docsExamined = planSummaryStats.totalDocsExamined;
+    additiveMetrics.keysExamined = planSummaryStats.totalKeysExamined;
+    additiveMetrics.docsExamined = planSummaryStats.totalDocsExamined;
     hasSortStage = planSummaryStats.hasSortStage;
     fromMultiPlanner = planSummaryStats.fromMultiPlanner;
     replanned = planSummaryStats.replanned;
 }
 
+namespace {
+
+/**
+ * Adds two boost::optional long longs together. Returns boost::none if both 'lhs' and 'rhs' are
+ * uninitialized, or the sum of 'lhs' and 'rhs' if they are both initialized. Returns 'lhs' if only
+ * 'rhs' is uninitialized and vice-versa.
+ */
+boost::optional<long long> addOptionalLongs(const boost::optional<long long>& lhs,
+                                            const boost::optional<long long>& rhs) {
+    if (!rhs) {
+        return lhs;
+    }
+    return lhs ? (*lhs + *rhs) : rhs;
+}
+}  // namespace
+
+void OpDebug::AdditiveMetrics::add(const AdditiveMetrics& otherMetrics) {
+    keysExamined = addOptionalLongs(keysExamined, otherMetrics.keysExamined);
+    docsExamined = addOptionalLongs(docsExamined, otherMetrics.docsExamined);
+    nMatched = addOptionalLongs(nMatched, otherMetrics.nMatched);
+    nModified = addOptionalLongs(nModified, otherMetrics.nModified);
+    ninserted = addOptionalLongs(ninserted, otherMetrics.ninserted);
+    ndeleted = addOptionalLongs(ndeleted, otherMetrics.ndeleted);
+    nmoved = addOptionalLongs(nmoved, otherMetrics.nmoved);
+    keysInserted = addOptionalLongs(keysInserted, otherMetrics.keysInserted);
+    keysDeleted = addOptionalLongs(keysDeleted, otherMetrics.keysDeleted);
+    prepareReadConflicts =
+        addOptionalLongs(prepareReadConflicts, otherMetrics.prepareReadConflicts);
+    writeConflicts = addOptionalLongs(writeConflicts, otherMetrics.writeConflicts);
+}
+
+void OpDebug::AdditiveMetrics::incrementWriteConflicts(long long n) {
+    if (!writeConflicts) {
+        writeConflicts = 0;
+    }
+    *writeConflicts += n;
+}
+
+void OpDebug::AdditiveMetrics::incrementKeysInserted(long long n) {
+    if (!keysInserted) {
+        keysInserted = 0;
+    }
+    *keysInserted += n;
+}
+
+void OpDebug::AdditiveMetrics::incrementKeysDeleted(long long n) {
+    if (!keysDeleted) {
+        keysDeleted = 0;
+    }
+    *keysDeleted += n;
+}
+
+void OpDebug::AdditiveMetrics::incrementNmoved(long long n) {
+    if (!nmoved) {
+        nmoved = 0;
+    }
+    *nmoved += n;
+}
+
+void OpDebug::AdditiveMetrics::incrementNinserted(long long n) {
+    if (!ninserted) {
+        ninserted = 0;
+    }
+    *ninserted += n;
+}
+
+void OpDebug::AdditiveMetrics::incrementPrepareReadConflicts(long long n) {
+    if (!prepareReadConflicts) {
+        prepareReadConflicts = 0;
+    }
+    *prepareReadConflicts += n;
+}
+
 }  // namespace mongo
diff --git a/src/mongo/db/curop.h b/src/mongo/db/curop.h
index a0d40523c84..bca2dbcac30 100644
--- a/src/mongo/db/curop.h
+++ b/src/mongo/db/curop.h
@@ -50,6 +50,69 @@ struct PlanSummaryStats;
 /* lifespan is different than CurOp because of recursives with DBDirectClient */
 class OpDebug {
 public:
+    /**
+     * Holds counters for execution statistics that are meaningful both for multi-statement
+     * transactions and for individual operations outside of a transaction.
+     */
+    class AdditiveMetrics {
+    public:
+        /**
+         * Adds all the fields of another AdditiveMetrics object together with the fields of this
+         * AdditiveMetrics instance.
+         */
+        void add(const AdditiveMetrics& otherMetrics);
+
+        /**
+         * Increments writeConflicts by n.
+         */
+        void incrementWriteConflicts(long long n);
+
+        /**
+         * Increments keysInserted by n.
+         */
+        void incrementKeysInserted(long long n);
+
+        /**
+         * Increments keysDeleted by n.
+         */
+        void incrementKeysDeleted(long long n);
+
+        /**
+         * Increments nmoved by n.
+         */
+        void incrementNmoved(long long n);
+
+        /**
+         * Increments ninserted by n.
+         */
+        void incrementNinserted(long long n);
+
+        /**
+         * Increments prepareReadConflicts by n.
+         */
+        void incrementPrepareReadConflicts(long long n);
+
+        boost::optional<long long> keysExamined;
+        boost::optional<long long> docsExamined;
+
+        // Number of records that match the query.
+        boost::optional<long long> nMatched;
+        // Number of records written (no no-ops).
+        boost::optional<long long> nModified;
+        boost::optional<long long> ninserted;
+        boost::optional<long long> ndeleted;
+
+        // Updates resulted in a move (moves are expensive).
+        boost::optional<long long> nmoved;
+        // Number of index keys inserted.
+        boost::optional<long long> keysInserted;
+        // Number of index keys removed.
+        boost::optional<long long> keysDeleted;
+        // Number of read conflicts caused by a prepared transaction.
+        boost::optional<long long> prepareReadConflicts;
+        boost::optional<long long> writeConflicts;
+    };
+
     OpDebug() = default;
 
     std::string report(Client* client,
@@ -88,10 +151,6 @@ public:
     long long ntoskip{-1};
     bool exhaust{false};
 
-    // debugging/profile info
-    long long keysExamined{-1};
-    long long docsExamined{-1};
-
     bool hasSortStage{false};  // true if the query plan involves an in-memory sort
 
     // True if the plan came from the multi-planner (not from the plan cache and not a query with a
@@ -101,23 +160,11 @@ public:
     // True if a replan was triggered during the execution of this operation.
     bool replanned{false};
 
-    long long nMatched{-1};   // number of records that match the query
-    long long nModified{-1};  // number of records written (no no-ops)
-    long long ninserted{-1};
-    long long ndeleted{-1};
     bool fastmodinsert{false};  // upsert of an $operation. builds a default object
     bool upsert{false};         // true if the update actually did an insert
     bool cursorExhausted{
         false};  // true if the cursor has been closed at end a find/getMore operation
 
-    // The following metrics are initialized with 0 rather than -1 in order to simplify use by the
-    // CRUD path.
-    long long nmoved{0};                // updates resulted in a move (moves are expensive)
-    long long keysInserted{0};          // Number of index keys inserted.
-    long long keysDeleted{0};           // Number of index keys removed.
-    long long prepareReadConflicts{0};  // Number of read conflicts caused by a prepared transaction
-    long long writeConflicts{0};
-
     BSONObj execStats;  // Owned here.
 
     // Details of any error (whether from an exception or a command returning failure).
@@ -130,6 +177,9 @@ public:
 
     // Shard targeting info.
     int nShards{-1};
+
+    // Stores additive metrics.
+    AdditiveMetrics additiveMetrics;
 };
 
 /**
diff --git a/src/mongo/db/curop_metrics.cpp b/src/mongo/db/curop_metrics.cpp
index be2ed8e00de..ac96709053a 100644
--- a/src/mongo/db/curop_metrics.cpp
+++ b/src/mongo/db/curop_metrics.cpp
@@ -64,21 +64,21 @@ void recordCurOpMetrics(OperationContext* opCtx) {
     const OpDebug& debug = CurOp::get(opCtx)->debug();
     if (debug.nreturned > 0)
         returnedCounter.increment(debug.nreturned);
-    if (debug.ninserted > 0)
-        insertedCounter.increment(debug.ninserted);
-    if (debug.nMatched > 0)
-        updatedCounter.increment(debug.nMatched);
-    if (debug.ndeleted > 0)
-        deletedCounter.increment(debug.ndeleted);
-    if (debug.keysExamined > 0)
-        scannedCounter.increment(debug.keysExamined);
-    if (debug.docsExamined > 0)
-        scannedObjectCounter.increment(debug.docsExamined);
+    if (debug.additiveMetrics.ninserted)
+        insertedCounter.increment(*debug.additiveMetrics.ninserted);
+    if (debug.additiveMetrics.nMatched)
+        updatedCounter.increment(*debug.additiveMetrics.nMatched);
+    if (debug.additiveMetrics.ndeleted)
+        deletedCounter.increment(*debug.additiveMetrics.ndeleted);
+    if (debug.additiveMetrics.keysExamined)
+        scannedCounter.increment(*debug.additiveMetrics.keysExamined);
+    if (debug.additiveMetrics.docsExamined)
+        scannedObjectCounter.increment(*debug.additiveMetrics.docsExamined);
 
     if (debug.hasSortStage)
         scanAndOrderCounter.increment();
-    if (debug.writeConflicts)
-        writeConflictsCounter.increment(debug.writeConflicts);
+    if (debug.additiveMetrics.writeConflicts)
+        writeConflictsCounter.increment(*debug.additiveMetrics.writeConflicts);
 }
 
 }  // namespace mongo
diff --git a/src/mongo/db/curop_test.cpp b/src/mongo/db/curop_test.cpp
new file mode 100644
index 00000000000..e0e281d336a
--- /dev/null
+++ b/src/mongo/db/curop_test.cpp
@@ -0,0 +1,172 @@
+/**
+ * Copyright (C) 2018 MongoDB Inc.
+ *
+ * This program is free software: you can redistribute it and/or  modify
+ * it under the terms of the GNU Affero General Public License, version 3,
+ * as published by the Free Software Foundation.
+ *
+ * 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
+ * GNU Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ * 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 GNU Affero General 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 <boost/optional/optional_io.hpp>
+
+#include "mongo/db/curop.h"
+#include "mongo/unittest/unittest.h"
+
+namespace mongo {
+namespace {
+
+TEST(CurOpTest, AddingAdditiveMetricsObjectsTogetherShouldAddFieldsTogether) {
+    OpDebug::AdditiveMetrics currentAdditiveMetrics = OpDebug::AdditiveMetrics();
+    OpDebug::AdditiveMetrics additiveMetricsToAdd = OpDebug::AdditiveMetrics();
+
+    // Initialize field values for both AdditiveMetrics objects.
+    currentAdditiveMetrics.keysExamined = 0;
+    additiveMetricsToAdd.keysExamined = 2;
+    currentAdditiveMetrics.docsExamined = 4;
+    additiveMetricsToAdd.docsExamined = 2;
+    currentAdditiveMetrics.nMatched = 5;
+    additiveMetricsToAdd.nMatched = 5;
+    currentAdditiveMetrics.nModified = 3;
+    additiveMetricsToAdd.nModified = 1;
+    currentAdditiveMetrics.ninserted = 4;
+    additiveMetricsToAdd.ninserted = 0;
+    currentAdditiveMetrics.ndeleted = 3;
+    additiveMetricsToAdd.ndeleted = 2;
+    currentAdditiveMetrics.nmoved = 0;
+    additiveMetricsToAdd.nmoved = 4;
+    currentAdditiveMetrics.keysInserted = 6;
+    additiveMetricsToAdd.keysInserted = 5;
+    currentAdditiveMetrics.keysDeleted = 4;
+    additiveMetricsToAdd.keysDeleted = 2;
+    currentAdditiveMetrics.prepareReadConflicts = 1;
+    additiveMetricsToAdd.prepareReadConflicts = 5;
+    currentAdditiveMetrics.writeConflicts = 7;
+    additiveMetricsToAdd.writeConflicts = 0;
+
+    // Save the current AdditiveMetrics object before adding.
+    OpDebug::AdditiveMetrics additiveMetricsBeforeAdd = currentAdditiveMetrics;
+    currentAdditiveMetrics.add(additiveMetricsToAdd);
+
+    // The following field values should have changed after adding.
+    ASSERT_EQ(*currentAdditiveMetrics.keysExamined,
+              *additiveMetricsBeforeAdd.keysExamined + *additiveMetricsToAdd.keysExamined);
+    ASSERT_EQ(*currentAdditiveMetrics.docsExamined,
+              *additiveMetricsBeforeAdd.docsExamined + *additiveMetricsToAdd.docsExamined);
+    ASSERT_EQ(*currentAdditiveMetrics.nMatched,
+              *additiveMetricsBeforeAdd.nMatched + *additiveMetricsToAdd.nMatched);
+    ASSERT_EQ(*currentAdditiveMetrics.nModified,
+              *additiveMetricsBeforeAdd.nModified + *additiveMetricsToAdd.nModified);
+    ASSERT_EQ(*currentAdditiveMetrics.ninserted,
+              *additiveMetricsBeforeAdd.ninserted + *additiveMetricsToAdd.ninserted);
+    ASSERT_EQ(*currentAdditiveMetrics.ndeleted,
+              *additiveMetricsBeforeAdd.ndeleted + *additiveMetricsToAdd.ndeleted);
+    ASSERT_EQ(*currentAdditiveMetrics.nmoved,
+              *additiveMetricsBeforeAdd.nmoved + *additiveMetricsToAdd.nmoved);
+    ASSERT_EQ(*currentAdditiveMetrics.keysInserted,
+              *additiveMetricsBeforeAdd.keysInserted + *additiveMetricsToAdd.keysInserted);
+    ASSERT_EQ(*currentAdditiveMetrics.keysDeleted,
+              *additiveMetricsBeforeAdd.keysDeleted + *additiveMetricsToAdd.keysDeleted);
+    ASSERT_EQ(*currentAdditiveMetrics.prepareReadConflicts,
+              *additiveMetricsBeforeAdd.prepareReadConflicts +
+                  *additiveMetricsToAdd.prepareReadConflicts);
+    ASSERT_EQ(*currentAdditiveMetrics.writeConflicts,
+              *additiveMetricsBeforeAdd.writeConflicts + *additiveMetricsToAdd.writeConflicts);
+}
+
+TEST(CurOpTest, AddingUninitializedAdditiveMetricsFieldsShouldBeTreatedAsZero) {
+    OpDebug::AdditiveMetrics currentAdditiveMetrics = OpDebug::AdditiveMetrics();
+    OpDebug::AdditiveMetrics additiveMetricsToAdd = OpDebug::AdditiveMetrics();
+
+    // Initialize field values for both AdditiveMetrics objects.
+    additiveMetricsToAdd.keysExamined = 5;
+    currentAdditiveMetrics.docsExamined = 4;
+    currentAdditiveMetrics.nModified = 3;
+    additiveMetricsToAdd.ninserted = 0;
+    currentAdditiveMetrics.nmoved = 0;
+    additiveMetricsToAdd.nmoved = 4;
+    currentAdditiveMetrics.keysInserted = 6;
+    additiveMetricsToAdd.keysInserted = 5;
+    currentAdditiveMetrics.keysDeleted = 4;
+    additiveMetricsToAdd.keysDeleted = 2;
+    currentAdditiveMetrics.prepareReadConflicts = 1;
+    additiveMetricsToAdd.prepareReadConflicts = 5;
+    currentAdditiveMetrics.writeConflicts = 7;
+    additiveMetricsToAdd.writeConflicts = 0;
+
+    // Save the current AdditiveMetrics object before adding.
+    OpDebug::AdditiveMetrics additiveMetricsBeforeAdd = currentAdditiveMetrics;
+    currentAdditiveMetrics.add(additiveMetricsToAdd);
+
+    // The 'keysExamined' field for the current AdditiveMetrics object was not initialized, so it
+    // should be treated as zero.
+    ASSERT_EQ(*currentAdditiveMetrics.keysExamined, *additiveMetricsToAdd.keysExamined);
+
+    // The 'docsExamined' field for the AdditiveMetrics object to add was not initialized, so it
+    // should be treated as zero.
+    ASSERT_EQ(*currentAdditiveMetrics.docsExamined, *additiveMetricsBeforeAdd.docsExamined);
+
+    // The 'nMatched' field for both the current AdditiveMetrics object and the AdditiveMetrics
+    // object to add were not initialized, so nMatched should still be uninitialized after the add.
+    ASSERT_EQ(currentAdditiveMetrics.nMatched, boost::none);
+
+    // The following field values should have changed after adding.
+    ASSERT_EQ(*currentAdditiveMetrics.nmoved,
+              *additiveMetricsBeforeAdd.nmoved + *additiveMetricsToAdd.nmoved);
+    ASSERT_EQ(*currentAdditiveMetrics.keysInserted,
+              *additiveMetricsBeforeAdd.keysInserted + *additiveMetricsToAdd.keysInserted);
+    ASSERT_EQ(*currentAdditiveMetrics.keysDeleted,
+              *additiveMetricsBeforeAdd.keysDeleted + *additiveMetricsToAdd.keysDeleted);
+    ASSERT_EQ(*currentAdditiveMetrics.prepareReadConflicts,
+              *additiveMetricsBeforeAdd.prepareReadConflicts +
+                  *additiveMetricsToAdd.prepareReadConflicts);
+    ASSERT_EQ(*currentAdditiveMetrics.writeConflicts,
+              *additiveMetricsBeforeAdd.writeConflicts + *additiveMetricsToAdd.writeConflicts);
+}
+
+TEST(CurOpTest, AdditiveMetricsFieldsShouldIncrementByN) {
+    OpDebug::AdditiveMetrics additiveMetrics = OpDebug::AdditiveMetrics();
+
+    // Initialize field values.
+    additiveMetrics.writeConflicts = 1;
+    additiveMetrics.keysInserted = 2;
+    additiveMetrics.prepareReadConflicts = 6;
+
+    // Increment the fields.
+    additiveMetrics.incrementWriteConflicts(1);
+    additiveMetrics.incrementKeysInserted(5);
+    additiveMetrics.incrementKeysDeleted(0);
+    additiveMetrics.incrementNmoved(1);
+    additiveMetrics.incrementNinserted(3);
+    additiveMetrics.incrementPrepareReadConflicts(2);
+
+    ASSERT_EQ(*additiveMetrics.writeConflicts, 2);
+    ASSERT_EQ(*additiveMetrics.keysInserted, 7);
+    ASSERT_EQ(*additiveMetrics.keysDeleted, 0);
+    ASSERT_EQ(*additiveMetrics.nmoved, 1);
+    ASSERT_EQ(*additiveMetrics.ninserted, 3);
+    ASSERT_EQ(*additiveMetrics.prepareReadConflicts, 8);
+}
+
+}  // namespace
+}  // namespace mongo
diff --git a/src/mongo/db/exec/update.cpp b/src/mongo/db/exec/update.cpp
index a044324197c..0673af4c73d 100644
--- a/src/mongo/db/exec/update.cpp
+++ b/src/mongo/db/exec/update.cpp
@@ -757,8 +757,8 @@ const UpdateStats* UpdateStage::getUpdateStats(const PlanExecutor* exec) {
 
 void UpdateStage::recordUpdateStatsInOpDebug(const UpdateStats* updateStats, OpDebug* opDebug) {
     invariant(opDebug);
-    opDebug->nMatched = updateStats->nMatched;
-    opDebug->nModified = updateStats->nModified;
+    opDebug->additiveMetrics.nMatched = updateStats->nMatched;
+    opDebug->additiveMetrics.nModified = updateStats->nModified;
     opDebug->upsert = updateStats->inserted;
     opDebug->fastmodinsert = updateStats->fastmodinsert;
 }
diff --git a/src/mongo/db/ops/write_ops_exec.cpp b/src/mongo/db/ops/write_ops_exec.cpp
index afea9ad96eb..9718457f0be 100644
--- a/src/mongo/db/ops/write_ops_exec.cpp
+++ b/src/mongo/db/ops/write_ops_exec.cpp
@@ -290,7 +290,7 @@ SingleWriteResult createIndex(OperationContext* opCtx,
     // Unlike normal inserts, it is not an error to "insert" a duplicate index.
     long long n =
         cmdResult["numIndexesAfter"].numberInt() - cmdResult["numIndexesBefore"].numberInt();
-    CurOp::get(opCtx)->debug().ninserted += n;
+    CurOp::get(opCtx)->debug().additiveMetrics.incrementNinserted(n);
 
     SingleWriteResult result;
     result.setN(n);
@@ -410,7 +410,7 @@ bool insertBatchAndHandleErrors(OperationContext* opCtx,
             result.setN(1);
 
             std::fill_n(std::back_inserter(out->results), batch.size(), std::move(result));
-            curOp.debug().ninserted += batch.size();
+            curOp.debug().additiveMetrics.incrementNinserted(batch.size());
             return true;
         }
     } catch (const DBException&) {
@@ -441,7 +441,7 @@ bool insertBatchAndHandleErrors(OperationContext* opCtx,
                     SingleWriteResult result;
                     result.setN(1);
                     out->results.emplace_back(std::move(result));
-                    curOp.debug().ninserted++;
+                    curOp.debug().additiveMetrics.incrementNinserted(1);
                 } catch (...) {
                     // Release the lock following any error if we are not in multi-statement
                     // transaction. Among other things, this ensures that we don't sleep in the WCE
@@ -505,7 +505,7 @@ WriteResult performInserts(OperationContext* opCtx, const write_ops::Insert& who
         curOp.setNS_inlock(wholeOp.getNamespace().ns());
         curOp.setLogicalOp_inlock(LogicalOp::opInsert);
         curOp.ensureStarted();
-        curOp.debug().ninserted = 0;
+        curOp.debug().additiveMetrics.ninserted = 0;
     }
 
     uassertStatusOK(userAllowedWriteNS(wholeOp.getNamespace()));
@@ -762,7 +762,7 @@ static SingleWriteResult performSingleDeleteOp(OperationContext* opCtx,
         curOp.ensureStarted();
     }
 
-    curOp.debug().ndeleted = 0;
+    curOp.debug().additiveMetrics.ndeleted = 0;
 
     DeleteRequest request(ns);
     request.setQuery(op.getQ());
@@ -802,7 +802,7 @@ static SingleWriteResult performSingleDeleteOp(OperationContext* opCtx,
 
     uassertStatusOK(exec->executePlan());
     long long n = DeleteStage::getNumDeleted(*exec);
-    curOp.debug().ndeleted = n;
+    curOp.debug().additiveMetrics.ndeleted = n;
 
     PlanSummaryStats summary;
     Explain::getSummaryStats(*exec, &summary);
diff --git a/src/mongo/db/query/plan_executor.cpp b/src/mongo/db/query/plan_executor.cpp
index 2eefdbbcb79..d34f429fdab 100644
--- a/src/mongo/db/query/plan_executor.cpp
+++ b/src/mongo/db/query/plan_executor.cpp
@@ -605,7 +605,7 @@ PlanExecutor::ExecState PlanExecutor::getNextImpl(Snapshotted<BSONObj>* objOut,
             if (id == WorkingSet::INVALID_ID) {
                 if (!_yieldPolicy->canAutoYield())
                     throw WriteConflictException();
-                CurOp::get(_opCtx)->debug().writeConflicts++;
+                CurOp::get(_opCtx)->debug().additiveMetrics.incrementWriteConflicts(1);
                 writeConflictsInARow++;
                 WriteConflictException::logAndBackoff(
                     writeConflictsInARow, "plan execution", _nss.ns());
diff --git a/src/mongo/db/query/plan_yield_policy.cpp b/src/mongo/db/query/plan_yield_policy.cpp
index b24f1787de1..6d493d40e4d 100644
--- a/src/mongo/db/query/plan_yield_policy.cpp
+++ b/src/mongo/db/query/plan_yield_policy.cpp
@@ -164,7 +164,7 @@ Status PlanYieldPolicy::yield(stdx::function<void()> beforeYieldingFn,
 
             return _planYielding->restoreStateWithoutRetrying();
         } catch (const WriteConflictException&) {
-            CurOp::get(opCtx)->debug().writeConflicts++;
+            CurOp::get(opCtx)->debug().additiveMetrics.incrementWriteConflicts(1);
             WriteConflictException::logAndBackoff(
                 attempt, "plan execution restoreState", _planYielding->nss().ns());
             // retry
diff --git a/src/mongo/db/storage/wiredtiger/wiredtiger_prepare_conflict.h b/src/mongo/db/storage/wiredtiger/wiredtiger_prepare_conflict.h
index 9bb45c928d8..8736d6db9b6 100644
--- a/src/mongo/db/storage/wiredtiger/wiredtiger_prepare_conflict.h
+++ b/src/mongo/db/storage/wiredtiger/wiredtiger_prepare_conflict.h
@@ -67,7 +67,7 @@ int wiredTigerPrepareConflictRetry(OperationContext* opCtx, F&& f) {
         if (ret != WT_PREPARE_CONFLICT)
             return ret;
 
-        ++CurOp::get(opCtx)->debug().prepareReadConflicts;
+        CurOp::get(opCtx)->debug().additiveMetrics.incrementPrepareReadConflicts(1);
         wiredTigerPrepareConflictLog(attempts);
         // Wait on the session cache to signal that a unit of work has been committed or aborted.
         recoveryUnit->getSessionCache()->waitUntilPreparedUnitOfWorkCommitsOrAborts(opCtx);
diff --git a/src/mongo/s/commands/cluster_write_cmd.cpp b/src/mongo/s/commands/cluster_write_cmd.cpp
index 0fa5aabde09..d97f24b34bb 100644
--- a/src/mongo/s/commands/cluster_write_cmd.cpp
+++ b/src/mongo/s/commands/cluster_write_cmd.cpp
@@ -273,22 +273,22 @@ private:
                 for (size_t i = 0; i < numAttempts; ++i) {
                     globalOpCounters.gotInsert();
                 }
-                debug.ninserted = response.getN();
+                debug.additiveMetrics.ninserted = response.getN();
                 break;
             case BatchedCommandRequest::BatchType_Update:
                 for (size_t i = 0; i < numAttempts; ++i) {
                     globalOpCounters.gotUpdate();
                 }
                 debug.upsert = response.isUpsertDetailsSet();
-                debug.nMatched =
+                debug.additiveMetrics.nMatched =
                     response.getN() - (debug.upsert ? response.sizeUpsertDetails() : 0);
-                debug.nModified = response.getNModified();
+                debug.additiveMetrics.nModified = response.getNModified();
                 break;
             case BatchedCommandRequest::BatchType_Delete:
                 for (size_t i = 0; i < numAttempts; ++i) {
                     globalOpCounters.gotDelete();
                 }
-                debug.ndeleted = response.getN();
+                debug.additiveMetrics.ndeleted = response.getN();
                 break;
         }