SERVER-43252: Only compute WriteConcernResult.writtenTo for CmdGetLastError

7 files changed, 18 insertions, 11 deletions

diff --git a/src/mongo/db/commands/get_last_error.cpp b/src/mongo/db/commands/get_last_error.cpp
index 1834aa60e63..2de7f05f169 100644
--- a/src/mongo/db/commands/get_last_error.cpp
+++ b/src/mongo/db/commands/get_last_error.cpp
@@ -279,6 +279,18 @@ public:
 
         WriteConcernResult wcResult;
         status = waitForWriteConcern(opCtx, lastOpTime, writeConcern, &wcResult);
+        // getLastError command returns a document that contains the writtenTo array. So we compute
+        // the writtenTo array here if we have waited for replication before. The call to
+        // getHostsWrittenTo needs to lock the ReplicationCoordinator mutex to guard against
+        // topology changes. Thus, we only compute this array here for the getLastError command
+        // (instead of in waitForWriteConcern for every single write) to avoid a serialization point
+        // for all writes.
+        if (!lastOpTime.isNull() && writeConcern.needToWaitForOtherNodes()) {
+            wcResult.writtenTo = replCoord->getHostsWrittenTo(
+                lastOpTime,
+                replCoord->populateUnsetWriteConcernOptionsSyncMode(writeConcern).syncMode ==
+                    WriteConcernOptions::SyncMode::JOURNAL);
+        }
         wcResult.appendTo(writeConcern, &result);
 
         // For backward compatibility with 2.4, wtimeout returns ok : 1.0
diff --git a/src/mongo/db/repl/replication_coordinator_impl.cpp b/src/mongo/db/repl/replication_coordinator_impl.cpp
index 03e4e7d74cb..90a7900bd4f 100644
--- a/src/mongo/db/repl/replication_coordinator_impl.cpp
+++ b/src/mongo/db/repl/replication_coordinator_impl.cpp
@@ -1758,7 +1758,7 @@ SharedSemiFuture<void> ReplicationCoordinatorImpl::_startWaitingForReplication(
         return Future<void>::makeReady(e.toStatus());
     }
 
-    if (!writeConcern.shouldWaitForOtherNodes() &&
+    if (!writeConcern.needToWaitForOtherNodes() &&
         writeConcern.syncMode != WriteConcernOptions::SyncMode::JOURNAL) {
         // We are only waiting for our own lastApplied, add this to _opTimeWaiterList instead. This
         // is because waiters in _replicationWaiterList are not notified on self's lastApplied
diff --git a/src/mongo/db/s/chunk_move_write_concern_options.cpp b/src/mongo/db/s/chunk_move_write_concern_options.cpp
index 4eb662043cb..66966957437 100644
--- a/src/mongo/db/s/chunk_move_write_concern_options.cpp
+++ b/src/mongo/db/s/chunk_move_write_concern_options.cpp
@@ -96,7 +96,7 @@ StatusWith<WriteConcernOptions> ChunkMoveWriteConcernOptions::getEffectiveWriteC
         writeConcern = getDefaultWriteConcernForMigration(opCtx);
     }
 
-    if (writeConcern.shouldWaitForOtherNodes() &&
+    if (writeConcern.needToWaitForOtherNodes() &&
         writeConcern.wTimeout == WriteConcernOptions::kNoTimeout) {
         // Don't allow no timeout
         writeConcern.wTimeout = durationCount<Milliseconds>(kDefaultWriteTimeoutForMigration);
diff --git a/src/mongo/db/s/migration_destination_manager.cpp b/src/mongo/db/s/migration_destination_manager.cpp
index c8817889615..946e6575468 100644
--- a/src/mongo/db/s/migration_destination_manager.cpp
+++ b/src/mongo/db/s/migration_destination_manager.cpp
@@ -852,7 +852,7 @@ void MigrationDestinationManager::_migrateDriver(OperationContext* opCtx) {
                         batchNumCloned);
                     _clonedBytes += batchClonedBytes;
                 }
-                if (_writeConcern.shouldWaitForOtherNodes()) {
+                if (_writeConcern.needToWaitForOtherNodes()) {
                     repl::ReplicationCoordinator::StatusAndDuration replStatus =
                         repl::ReplicationCoordinator::get(opCtx)->awaitReplication(
                             opCtx,
diff --git a/src/mongo/db/write_concern.cpp b/src/mongo/db/write_concern.cpp
index a1ea9c5bf92..70b9e22dbb3 100644
--- a/src/mongo/db/write_concern.cpp
+++ b/src/mongo/db/write_concern.cpp
@@ -218,8 +218,7 @@ Status waitForWriteConcern(OperationContext* opCtx,
     }
 
     // needed to avoid incrementing gleWtimeStats SERVER-9005
-    if (writeConcernWithPopulatedSyncMode.wNumNodes <= 1 &&
-        writeConcernWithPopulatedSyncMode.wMode.empty()) {
+    if (!writeConcernWithPopulatedSyncMode.needToWaitForOtherNodes()) {
         // no desired replication check
         return Status::OK();
     }
@@ -233,10 +232,6 @@ Status waitForWriteConcern(OperationContext* opCtx,
         result->wTimedOut = true;
     }
 
-    // Add stats
-    result->writtenTo = replCoord->getHostsWrittenTo(replOpTime,
-                                                     writeConcernWithPopulatedSyncMode.syncMode ==
-                                                         WriteConcernOptions::SyncMode::JOURNAL);
     gleWtimeStats.recordMillis(durationCount<Milliseconds>(replStatus.duration));
     result->wTime = durationCount<Milliseconds>(replStatus.duration);
 
diff --git a/src/mongo/db/write_concern_options.cpp b/src/mongo/db/write_concern_options.cpp
index d92dbfed25c..1ad40acebfd 100644
--- a/src/mongo/db/write_concern_options.cpp
+++ b/src/mongo/db/write_concern_options.cpp
@@ -242,7 +242,7 @@ BSONObj WriteConcernOptions::toBSON() const {
     return builder.obj();
 }
 
-bool WriteConcernOptions::shouldWaitForOtherNodes() const {
+bool WriteConcernOptions::needToWaitForOtherNodes() const {
     return !wMode.empty() || wNumNodes > 1;
 }
 
diff --git a/src/mongo/db/write_concern_options.h b/src/mongo/db/write_concern_options.h
index 99a6bff9fc2..39025832ea0 100644
--- a/src/mongo/db/write_concern_options.h
+++ b/src/mongo/db/write_concern_options.h
@@ -93,7 +93,7 @@ public:
      * Return true if the server needs to wait for other secondary nodes to satisfy this
      * write concern setting. Errs on the false positive for non-empty wMode.
      */
-    bool shouldWaitForOtherNodes() const;
+    bool needToWaitForOtherNodes() const;
 
     void reset() {
         syncMode = SyncMode::UNSET;