SERVER-35149 Track total number of open transactions in ServerTransactionsMetrics

5 files changed, 86 insertions, 1 deletions

diff --git a/src/mongo/db/server_transactions_metrics.cpp b/src/mongo/db/server_transactions_metrics.cpp
index fe31687f288..07319300f74 100644
--- a/src/mongo/db/server_transactions_metrics.cpp
+++ b/src/mongo/db/server_transactions_metrics.cpp
@@ -51,6 +51,18 @@ ServerTransactionsMetrics* ServerTransactionsMetrics::get(OperationContext* opCt
     return get(opCtx->getServiceContext());
 }
 
+unsigned long long ServerTransactionsMetrics::getCurrentOpen() const {
+    return _currentOpen.load();
+}
+
+void ServerTransactionsMetrics::decrementCurrentOpen() {
+    _currentOpen.fetchAndSubtract(1);
+}
+
+void ServerTransactionsMetrics::incrementCurrentOpen() {
+    _currentOpen.fetchAndAdd(1);
+}
+
 unsigned long long ServerTransactionsMetrics::getTotalStarted() const {
     return _totalStarted.load();
 }
diff --git a/src/mongo/db/server_transactions_metrics.h b/src/mongo/db/server_transactions_metrics.h
index a9e2490cf88..22892d37944 100644
--- a/src/mongo/db/server_transactions_metrics.h
+++ b/src/mongo/db/server_transactions_metrics.h
@@ -46,6 +46,10 @@ public:
     static ServerTransactionsMetrics* get(ServiceContext* service);
     static ServerTransactionsMetrics* get(OperationContext* opCtx);
 
+    unsigned long long getCurrentOpen() const;
+    void decrementCurrentOpen();
+    void incrementCurrentOpen();
+
     unsigned long long getTotalStarted() const;
     void incrementTotalStarted();
 
@@ -61,6 +65,9 @@ public:
     void updateStats(TransactionsStats* stats);
 
 private:
+    // The total number of open transactions.
+    AtomicUInt64 _currentOpen{0};
+
     // The total number of multi-document transactions started since the last server startup.
     AtomicUInt64 _totalStarted{0};
 
diff --git a/src/mongo/db/session.cpp b/src/mongo/db/session.cpp
index 4f3afc8b8ae..b3dc45168fd 100644
--- a/src/mongo/db/session.cpp
+++ b/src/mongo/db/session.cpp
@@ -607,6 +607,7 @@ void Session::_beginOrContinueTxn(WithLock wl,
             Date_t::fromMillisSinceEpoch(_singleTransactionStats->getStartTime() / 1000) +
             stdx::chrono::seconds{transactionLifetimeLimitSeconds.load()};
         ServerTransactionsMetrics::get(getGlobalServiceContext())->incrementTotalStarted();
+        ServerTransactionsMetrics::get(getGlobalServiceContext())->incrementCurrentOpen();
     } else {
         // Execute a retryable write or snapshot read.
         invariant(startTransaction == boost::none);
@@ -914,6 +915,7 @@ void Session::_abortTransaction(WithLock wl) {
     if (isMultiDocumentTransaction) {
         _singleTransactionStats->setEndTime(curTimeMicros64());
     }
+    ServerTransactionsMetrics::get(getGlobalServiceContext())->decrementCurrentOpen();
 }
 
 void Session::_beginOrContinueTxnOnMigration(WithLock wl, TxnNumber txnNumber) {
@@ -1049,6 +1051,7 @@ void Session::_commitTransaction(stdx::unique_lock<stdx::mutex> lk, OperationCon
     if (isMultiDocumentTransaction) {
         _singleTransactionStats->setEndTime(curTimeMicros64());
     }
+    ServerTransactionsMetrics::get(opCtx)->decrementCurrentOpen();
 }
 
 BSONObj Session::reportStashedState() const {
diff --git a/src/mongo/db/session_test.cpp b/src/mongo/db/session_test.cpp
index a29ffb11c69..0104f0d6fa0 100644
--- a/src/mongo/db/session_test.cpp
+++ b/src/mongo/db/session_test.cpp
@@ -1235,6 +1235,66 @@ TEST_F(SessionTest, IncrementTotalAbortedUponAbort) {
     ASSERT_EQ(ServerTransactionsMetrics::get(opCtx())->getTotalAborted(), beforeAbortCount + 1U);
 }
 
+TEST_F(SessionTest, TrackTotalOpenTransactionsWithAbort) {
+    const auto sessionId = makeLogicalSessionIdForTest();
+    Session session(sessionId);
+    session.refreshFromStorageIfNeeded(opCtx());
+
+    unsigned long long beforeTransactionStart =
+        ServerTransactionsMetrics::get(opCtx())->getCurrentOpen();
+
+    const TxnNumber txnNum = 1;
+    opCtx()->setLogicalSessionId(sessionId);
+    opCtx()->setTxnNumber(txnNum);
+
+    // Tests that starting a transaction increments the open transactions counter by 1.
+    session.beginOrContinueTxn(opCtx(), txnNum, false, true, "testDB", "insert");
+    session.unstashTransactionResources(opCtx(), "insert");
+    ASSERT_EQ(ServerTransactionsMetrics::get(opCtx())->getCurrentOpen(),
+              beforeTransactionStart + 1U);
+
+    // Tests that stashing the transaction resources does not affect the open transactions counter.
+    { Lock::GlobalLock lk(opCtx(), MODE_IX, Date_t::now(), Lock::InterruptBehavior::kThrow); }
+    session.stashTransactionResources(opCtx());
+    ASSERT_EQ(ServerTransactionsMetrics::get(opCtx())->getCurrentOpen(),
+              beforeTransactionStart + 1U);
+
+    // Tests that aborting a transaction decrements the open transactions counter by 1.
+    session.abortArbitraryTransaction();
+    ASSERT_EQ(ServerTransactionsMetrics::get(opCtx())->getCurrentOpen(), beforeTransactionStart);
+}
+
+TEST_F(SessionTest, TrackTotalOpenTransactionsWithCommit) {
+    const auto sessionId = makeLogicalSessionIdForTest();
+    Session session(sessionId);
+    session.refreshFromStorageIfNeeded(opCtx());
+
+    unsigned long long beforeTransactionStart =
+        ServerTransactionsMetrics::get(opCtx())->getCurrentOpen();
+
+    const TxnNumber txnNum = 1;
+    opCtx()->setLogicalSessionId(sessionId);
+    opCtx()->setTxnNumber(txnNum);
+
+    // Tests that starting a transaction increments the open transactions counter by 1.
+    session.beginOrContinueTxn(opCtx(), txnNum, false, true, "testDB", "insert");
+    session.unstashTransactionResources(opCtx(), "insert");
+    ASSERT_EQ(ServerTransactionsMetrics::get(opCtx())->getCurrentOpen(),
+              beforeTransactionStart + 1U);
+
+    // Tests that stashing the transaction resources does not affect the open transactions counter.
+    { Lock::GlobalLock lk(opCtx(), MODE_IX, Date_t::now(), Lock::InterruptBehavior::kThrow); }
+    session.stashTransactionResources(opCtx());
+    ASSERT_EQ(ServerTransactionsMetrics::get(opCtx())->getCurrentOpen(),
+              beforeTransactionStart + 1U);
+
+    session.unstashTransactionResources(opCtx(), "insert");
+
+    // Tests that committing a transaction decrements the open transactions counter by 1.
+    session.commitTransaction(opCtx());
+    ASSERT_EQ(ServerTransactionsMetrics::get(opCtx())->getCurrentOpen(), beforeTransactionStart);
+}
+
 /**
  * Test fixture for transactions metrics.
  */
@@ -1382,4 +1442,4 @@ TEST_F(TransactionsMetricsTest, SingleTransactionStatsDurationShouldKeepIncreasi
 }
 
 }  // namespace
-}  // namespace mongo
+}  // namespace mongo
\ No newline at end of file
diff --git a/src/mongo/db/transactions_stats.idl b/src/mongo/db/transactions_stats.idl
index 34b4b954c0f..3987ba0be8e 100644
--- a/src/mongo/db/transactions_stats.idl
+++ b/src/mongo/db/transactions_stats.idl
@@ -36,6 +36,9 @@ structs:
       retriedStatementsCount:
         type: long
         default: 0
+      currentOpen:
+        type: long
+        default: 0
       totalAborted:
         type: long
         default: 0