SERVER-43769: Only get the default write concern from ReplSetConfig if no write concern is specified

5 files changed, 29 insertions, 46 deletions

diff --git a/src/mongo/db/repl/repl_set_config.cpp b/src/mongo/db/repl/repl_set_config.cpp
index 434af8db845..6fa81e2aeb4 100644
--- a/src/mongo/db/repl/repl_set_config.cpp
+++ b/src/mongo/db/repl/repl_set_config.cpp
@@ -325,8 +325,7 @@ Status ReplSetConfig::_parseSettingsSubdocument(const BSONObj& settings) {
             return status;
     } else if (status == ErrorCodes::NoSuchKey) {
         // Default write concern is w: 1.
-        _defaultWriteConcern.reset();
-        _defaultWriteConcern.wNumNodes = 1;
+        _defaultWriteConcern = WriteConcernOptions();
     } else {
         return status;
     }
diff --git a/src/mongo/db/write_concern.cpp b/src/mongo/db/write_concern.cpp
index 8f05f50e370..30c01e5a831 100644
--- a/src/mongo/db/write_concern.cpp
+++ b/src/mongo/db/write_concern.cpp
@@ -72,14 +72,24 @@ StatusWith<WriteConcernOptions> extractWriteConcern(OperationContext* opCtx,
                                                     const BSONObj& cmdObj) {
     // The default write concern if empty is {w:1}. Specifying {w:0} is/was allowed, but is
     // interpreted identically to {w:1}.
-    auto wcResult = WriteConcernOptions::extractWCFromCommand(
-        cmdObj, repl::ReplicationCoordinator::get(opCtx)->getGetLastErrorDefault());
+    auto wcResult = WriteConcernOptions::extractWCFromCommand(cmdObj);
     if (!wcResult.isOK()) {
         return wcResult.getStatus();
     }
 
     WriteConcernOptions writeConcern = wcResult.getValue();
 
+    // Get the default write concern specified in ReplSetConfig only if no write concern is
+    // specified in the command (when usedDefault is true) to avoid locking the
+    // ReplicationCoordinator mutex unconditionally.
+    if (writeConcern.usedDefault) {
+        writeConcern = repl::ReplicationCoordinator::get(opCtx)->getGetLastErrorDefault();
+        if (writeConcern.wNumNodes == 0 && writeConcern.wMode.empty()) {
+            writeConcern.wNumNodes = 1;
+        }
+        writeConcern.usedDefaultW = true;
+    }
+
     if (writeConcern.usedDefault && serverGlobalParams.clusterRole == ClusterRole::ConfigServer &&
         !opCtx->getClient()->isInDirectClient() &&
         (opCtx->getClient()->session() &&
diff --git a/src/mongo/db/write_concern_options.cpp b/src/mongo/db/write_concern_options.cpp
index 1ad40acebfd..22bb5b49790 100644
--- a/src/mongo/db/write_concern_options.cpp
+++ b/src/mongo/db/write_concern_options.cpp
@@ -92,7 +92,7 @@ WriteConcernOptions::WriteConcernOptions(const std::string& mode,
     : syncMode(sync), wNumNodes(0), wMode(mode), wTimeout(durationCount<Milliseconds>(timeout)) {}
 
 Status WriteConcernOptions::parse(const BSONObj& obj) {
-    reset();
+    *this = WriteConcernOptions();
     if (obj.isEmpty()) {
         return Status(ErrorCodes::FailedToParse, "write concern object cannot be empty");
     }
@@ -148,6 +148,7 @@ Status WriteConcernOptions::parse(const BSONObj& obj) {
         wNumNodes = wEl.numberInt();
         usedDefaultW = false;
     } else if (wEl.type() == String) {
+        wNumNodes = 0;
         wMode = wEl.valuestrsafe();
         usedDefaultW = false;
     } else if (wEl.eoo() || wEl.type() == jstNULL || wEl.type() == Undefined) {
@@ -159,37 +160,16 @@ Status WriteConcernOptions::parse(const BSONObj& obj) {
     return Status::OK();
 }
 
-namespace {
-
-/**
- * Construct a WriteConcernOptions based on an optional default WC object, in preparation for
- * parsing out of a command object or IDL.
- */
-WriteConcernOptions constructWCFromDefault(
-    const WriteConcernOptions& defaultWC = WriteConcernOptions()) {
-    WriteConcernOptions writeConcern = defaultWC;
-    writeConcern.usedDefault = true;
-    writeConcern.usedDefaultW = true;
-    if (writeConcern.wNumNodes == 0 && writeConcern.wMode.empty()) {
-        writeConcern.wNumNodes = 1;
-    }
-    return writeConcern;
-}
-
-}  // namespace
-
-
 WriteConcernOptions WriteConcernOptions::deserializerForIDL(const BSONObj& obj) {
-    WriteConcernOptions writeConcern = constructWCFromDefault();
+    WriteConcernOptions writeConcern;
     if (!obj.isEmpty()) {
         uassertStatusOK(writeConcern.parse(obj));
     }
     return writeConcern;
 }
 
-StatusWith<WriteConcernOptions> WriteConcernOptions::extractWCFromCommand(
-    const BSONObj& cmdObj, const WriteConcernOptions& defaultWC) {
-    WriteConcernOptions writeConcern = constructWCFromDefault(defaultWC);
+StatusWith<WriteConcernOptions> WriteConcernOptions::extractWCFromCommand(const BSONObj& cmdObj) {
+    WriteConcernOptions writeConcern;
 
     // Return the default write concern if no write concern is provided. We check for the existence
     // of the write concern field up front in order to avoid the expense of constructing an error
diff --git a/src/mongo/db/write_concern_options.h b/src/mongo/db/write_concern_options.h
index 39025832ea0..c20ba6287fa 100644
--- a/src/mongo/db/write_concern_options.h
+++ b/src/mongo/db/write_concern_options.h
@@ -57,13 +57,16 @@ public:
     static constexpr Seconds kWriteConcernTimeoutSharding{60};
     static constexpr Seconds kWriteConcernTimeoutUserCommand{60};
 
-    WriteConcernOptions() {
-        reset();
-        // It is assumed that a default-constructed WriteConcernOptions will be populated with the
-        // default options. If it is subsequently populated with non-default options, it is the
-        // caller's responsibility to set this flag accordingly.
-        usedDefault = true;
-    }
+    // It is assumed that a default-constructed WriteConcernOptions will be populated with the
+    // default options. If it is subsequently populated with non-default options, it is the caller's
+    // responsibility to set the usedDefault and usedDefaultW flag correctly.
+    WriteConcernOptions()
+        : syncMode(SyncMode::UNSET),
+          wNumNodes(1),
+          wMode(""),
+          wTimeout(0),
+          usedDefault(true),
+          usedDefaultW(true) {}
 
     WriteConcernOptions(int numNodes, SyncMode sync, int timeout);
 
@@ -86,8 +89,7 @@ public:
      * Attempts to extract a writeConcern from cmdObj.
      * Verifies that the writeConcern is of type Object (BSON type).
      */
-    static StatusWith<WriteConcernOptions> extractWCFromCommand(
-        const BSONObj& cmdObj, const WriteConcernOptions& defaultWC = WriteConcernOptions());
+    static StatusWith<WriteConcernOptions> extractWCFromCommand(const BSONObj& cmdObj);
 
     /**
      * Return true if the server needs to wait for other secondary nodes to satisfy this
@@ -95,13 +97,6 @@ public:
      */
     bool needToWaitForOtherNodes() const;
 
-    void reset() {
-        syncMode = SyncMode::UNSET;
-        wNumNodes = 0;
-        wMode = "";
-        wTimeout = 0;
-    }
-
     // Returns the BSON representation of this object.
     // Warning: does not return the same object passed on the last parse() call.
     BSONObj toBSON() const;
diff --git a/src/mongo/s/catalog/sharding_catalog_client_impl.cpp b/src/mongo/s/catalog/sharding_catalog_client_impl.cpp
index 4776fed9ed3..4ced819df8a 100644
--- a/src/mongo/s/catalog/sharding_catalog_client_impl.cpp
+++ b/src/mongo/s/catalog/sharding_catalog_client_impl.cpp
@@ -590,7 +590,6 @@ bool ShardingCatalogClientImpl::runUserManagementWriteCommand(OperationContext*
         // Make sure that if the command has a write concern that it is w:1 or w:majority, and
         // convert w:1 or no write concern to w:majority before sending.
         WriteConcernOptions writeConcern;
-        writeConcern.reset();
 
         BSONElement writeConcernElement = cmdObj[WriteConcernOptions::kWriteConcernField];
         bool initialCmdHadWriteConcern = !writeConcernElement.eoo();