SERVER-39187 Signal coordinator's decision promise when the coordinator is canceled before beginning commit

7 files changed, 35 insertions, 3 deletions

diff --git a/src/mongo/db/s/txn_two_phase_commit_cmds.cpp b/src/mongo/db/s/txn_two_phase_commit_cmds.cpp
index eaa2a9ba36a..d458006ffdb 100644
--- a/src/mongo/db/s/txn_two_phase_commit_cmds.cpp
+++ b/src/mongo/db/s/txn_two_phase_commit_cmds.cpp
@@ -244,6 +244,9 @@ public:
                 // The commit coordination is still ongoing. Block waiting for the decision.
                 auto commitDecision = commitDecisionFuture->get(opCtx);
                 switch (commitDecision) {
+                    case txn::CommitDecision::kCanceled:
+                        // Continue on to recover the commit decision from disk.
+                        break;
                     case txn::CommitDecision::kAbort:
                         uasserted(ErrorCodes::NoSuchTransaction, "Transaction was aborted");
                     case txn::CommitDecision::kCommit:
diff --git a/src/mongo/db/transaction_coordinator.cpp b/src/mongo/db/transaction_coordinator.cpp
index 463cdb879a8..1040735154e 100644
--- a/src/mongo/db/transaction_coordinator.cpp
+++ b/src/mongo/db/transaction_coordinator.cpp
@@ -176,6 +176,8 @@ Future<void> TransactionCoordinator::onCompletion() {
 void TransactionCoordinator::cancelIfCommitNotYetStarted() {
     stdx::unique_lock<stdx::mutex> lk(_mutex);
     if (_state == CoordinatorState::kInit) {
+        invariant(!_finalDecisionPromise.getFuture().isReady());
+        _finalDecisionPromise.emplaceValue(txn::CommitDecision::kCanceled);
         _transitionToDone(std::move(lk));
     }
 }
@@ -195,6 +197,8 @@ Future<void> TransactionCoordinator::_sendDecisionToParticipants(
         case txn::CommitDecision::kAbort:
             _state = CoordinatorState::kAborting;
             return _driver.sendAbort(participantShards, _lsid, _txnNumber);
+        case txn::CommitDecision::kCanceled:
+            MONGO_UNREACHABLE;
     };
     MONGO_UNREACHABLE;
 };
diff --git a/src/mongo/db/transaction_coordinator.h b/src/mongo/db/transaction_coordinator.h
index 063e32e209a..2fb6bfa0cef 100644
--- a/src/mongo/db/transaction_coordinator.h
+++ b/src/mongo/db/transaction_coordinator.h
@@ -226,8 +226,9 @@ inline logger::LogstreamBuilder& operator<<(logger::LogstreamBuilder& stream,
                                             const txn::CommitDecision& decision) {
     // clang-format off
     switch (decision) {
-        case txn::CommitDecision::kCommit:  stream.stream() << "kCommit"; break;
-        case txn::CommitDecision::kAbort:   stream.stream() << "kAbort"; break;
+        case txn::CommitDecision::kCommit:     stream.stream() << "kCommit"; break;
+        case txn::CommitDecision::kAbort:      stream.stream() << "kAbort"; break;
+        case txn::CommitDecision::kCanceled:   stream.stream() << "kCanceled"; break;
     };
     // clang-format on
     return stream;
diff --git a/src/mongo/db/transaction_coordinator_driver.cpp b/src/mongo/db/transaction_coordinator_driver.cpp
index 9e78746bed0..1853053139c 100644
--- a/src/mongo/db/transaction_coordinator_driver.cpp
+++ b/src/mongo/db/transaction_coordinator_driver.cpp
@@ -280,6 +280,11 @@ Future<txn::PrepareVoteConsensus> TransactionCoordinatorDriver::sendPrepare(
                         ? std::max(result.maxPrepareTimestamp, next.prepareTimestamp)
                         : next.prepareTimestamp;
                     break;
+                case PrepareVote::kCanceled:
+                    // PrepareVote is just an alias for CommitDecision, so we need to include this
+                    // branch as part of the switch statement, but CommitDecision::kCanceled will
+                    // never be a valid response to prepare so this path is unreachable.
+                    MONGO_UNREACHABLE;
             }
 
             return txn::ShouldStopIteration::kNo;
diff --git a/src/mongo/db/transaction_coordinator_driver.h b/src/mongo/db/transaction_coordinator_driver.h
index a92d97f8174..62354189320 100644
--- a/src/mongo/db/transaction_coordinator_driver.h
+++ b/src/mongo/db/transaction_coordinator_driver.h
@@ -46,6 +46,7 @@ namespace txn {
 enum class CommitDecision {
     kCommit,
     kAbort,
+    kCanceled,
 };
 
 /**
diff --git a/src/mongo/db/transaction_coordinator_futures_util_test.cpp b/src/mongo/db/transaction_coordinator_futures_util_test.cpp
index 86754e7ef60..ecb4ed5ba66 100644
--- a/src/mongo/db/transaction_coordinator_futures_util_test.cpp
+++ b/src/mongo/db/transaction_coordinator_futures_util_test.cpp
@@ -300,7 +300,7 @@ TEST_F(DoWhileTest, LoopBodyExecutesAtLeastOnceWithBackoff) {
 TEST_F(DoWhileTest, LoopBodyExecutesManyIterationsWithoutBackoff) {
     AsyncWorkScheduler async(getServiceContext());
 
-    int remainingLoops = 100'000;
+    int remainingLoops = 1000;
     auto future = doWhile(async,
                           boost::none,
                           [&remainingLoops](const StatusWith<int>& status) {
diff --git a/src/mongo/db/transaction_coordinator_service_test.cpp b/src/mongo/db/transaction_coordinator_service_test.cpp
index 05aaa06b759..28c0bcb9780 100644
--- a/src/mongo/db/transaction_coordinator_service_test.cpp
+++ b/src/mongo/db/transaction_coordinator_service_test.cpp
@@ -382,6 +382,24 @@ TEST_F(TransactionCoordinatorServiceTest, RecoverCommitJoinsOngoingCoordinationT
               static_cast<int>(commitDecisionFuture2.get()));
 }
 
+TEST_F(TransactionCoordinatorServiceTest,
+       RecoverCommitWorksIfCommitNeverReceivedAndCoordinationCanceled) {
+    auto coordinatorService = TransactionCoordinatorService::get(operationContext());
+
+    coordinatorService->createCoordinator(operationContext(), _lsid, _txnNumber, kCommitDeadline);
+
+    auto commitDecisionFuture =
+        *coordinatorService->recoverCommit(operationContext(), _lsid, _txnNumber);
+
+    // Cancel previous coordinator by creating a new coordinator at a higher txn number.
+    coordinatorService->createCoordinator(
+        operationContext(), _lsid, _txnNumber + 1, kCommitDeadline);
+
+
+    ASSERT_EQ(static_cast<int>(commitDecisionFuture.get()),
+              static_cast<int>(txn::CommitDecision::kCanceled));
+}
+
 TEST_F(
     TransactionCoordinatorServiceTest,
     CreateCoordinatorWithHigherTxnNumberThanExistingButNotYetCommittingTxnCancelsPreviousTxnAndSucceeds) {