fix(NODE-6436): only force majority write concern on commitTransaction retry

src/sessions.ts

@@ -124,6 +124,10 @@ export class ClientSession
   owner?: symbol | AbstractCursor;
   defaultTransactionOptions: TransactionOptions;
   transaction: Transaction;
+  /** @internal
+   * Keeps track of whether or not the current transaction has attempted to be committed. Is
+   * initially undefined. Gets set to false when startTransaction is called. When commitTransaction is sent to server, if the commitTransaction succeeds, it is then set to undefined, otherwise, set to true */
+  commitAttempted?: boolean;
   /** @internal */
   [kServerSession]: ServerSession | null;
   /** @internal */
@@ -417,6 +421,7 @@ export class ClientSession
       );
     }
 
+    this.commitAttempted = false;
     // increment txnNumber
     this.incrementTransactionNumber();
     // create transaction state
@@ -474,7 +479,7 @@ export class ClientSession
       WriteConcern.apply(command, { wtimeoutMS: 10000, w: 'majority', ...wc });
     }
 
-    if (this.transaction.state === TxnState.TRANSACTION_COMMITTED) {
+    if (this.transaction.state === TxnState.TRANSACTION_COMMITTED || this.commitAttempted) {
       WriteConcern.apply(command, { wtimeoutMS: 10000, ...wc, w: 'majority' });
     }
 
@@ -494,16 +499,25 @@ export class ClientSession
 
     try {
       await executeOperation(this.client, operation);
+      this.commitAttempted = undefined;
       return;
     } catch (firstCommitError) {
+      this.commitAttempted = true;
       if (firstCommitError instanceof MongoError && isRetryableWriteError(firstCommitError)) {
         // SPEC-1185: apply majority write concern when retrying commitTransaction
         WriteConcern.apply(command, { wtimeoutMS: 10000, ...wc, w: 'majority' });
         // per txns spec, must unpin session in this case
         this.unpin({ force: true });
 
         try {
-          await executeOperation(this.client, operation);
+          await executeOperation(
+            this.client,
+            new RunAdminCommandOperation(command, {
+              session: this,
+              readPreference: ReadPreference.primary,
+              bypassPinningCheck: true
+            })
+          );
           return;
         } catch (retryCommitError) {
           // If the retry failed, we process that error instead of the original

test/integration/transactions/transactions.test.ts

@@ -3,6 +3,7 @@ import { expect } from 'chai';
 import {
   ClientSession,
   type Collection,
+  type CommandStartedEvent,
   type MongoClient,
   MongoInvalidArgumentError,
   MongoNetworkError,
@@ -231,8 +232,13 @@ describe('Transactions', function () {
 
   context('when completing a transaction', () => {
     let client: MongoClient;
+    let commandsStarted: CommandStartedEvent[];
     beforeEach(async function () {
-      client = this.configuration.newClient();
+      client = this.configuration.newClient(undefined, { monitorCommands: true });
+      commandsStarted = [];
+      client.on('commandStarted', ev => {
+        commandsStarted.push(ev);
+      });
     });
 
     afterEach(async function () {
@@ -260,6 +266,30 @@ describe('Transactions', function () {
           })
         )
     );
+
+    it(
+      'commitTransaction does not override write concern on initial attempt',
+      { requires: { mongodb: '>=4.2.0', topology: '!single' } },
+      async function () {
+        await client
+          .db('test')
+          .dropCollection('test')
+          .catch(() => null);
+        const collection = await client.db('test').createCollection('test');
+        const session = client.startSession({
+          defaultTransactionOptions: { writeConcern: { w: 1 } }
+        });
+        session.startTransaction();
+        await collection.insertOne({ x: 1 }, { session });
+        await session.commitTransaction();
+
+        const commitTransactions = commandsStarted.filter(
+          x => x.commandName === 'commitTransaction'
+        );
+        expect(commitTransactions).to.have.lengthOf(1);
+        expect(commitTransactions[0].command).to.have.nested.property('writeConcern.w', 1);
+      }
+    );
   });
 
   describe('TransientTransactionError', function () {