SERVER-40298 Track transaction size

5 files changed, 152 insertions, 18 deletions

diff --git a/jstests/noPassthrough/server_transaction_metrics_last_committed_transaction.js b/jstests/noPassthrough/server_transaction_metrics_last_committed_transaction.js
new file mode 100644
index 00000000000..7f5faa9e4f8
--- /dev/null
+++ b/jstests/noPassthrough/server_transaction_metrics_last_committed_transaction.js
@@ -0,0 +1,86 @@
+// Tests the 'lastCommittedTransaction' serverStatus section.
+// @tags: [uses_transactions]
+(function() {
+    "use strict";
+
+    const rst = new ReplSetTest({nodes: 1});
+    rst.startSet();
+    rst.initiate();
+    const primary = rst.getPrimary();
+
+    const dbName = "test";
+    const collName = "coll";
+
+    const sessionOptions = {causalConsistency: false};
+    const session = primary.getDB(dbName).getMongo().startSession(sessionOptions);
+    const sessionDb = session.getDatabase(dbName);
+    const sessionColl = sessionDb[collName];
+    assert.commandWorked(sessionDb.runCommand({create: collName}));
+
+    function checkLastCommittedTransaction(operationCount, writeConcern) {
+        let res = assert.commandWorked(primary.adminCommand({serverStatus: 1}));
+        assert(res.hasOwnProperty("transactions"), tojson(res));
+        assert(res.transactions.hasOwnProperty("lastCommittedTransaction"),
+               tojson(res.transactions));
+        assert.eq(operationCount,
+                  res.transactions.lastCommittedTransaction.operationCount,
+                  tojson(res.transactions));
+        if (operationCount === 0) {
+            assert.eq(0,
+                      res.transactions.lastCommittedTransaction.oplogOperationBytes,
+                      tojson(res.transactions));
+        } else {
+            assert.lt(0,
+                      res.transactions.lastCommittedTransaction.oplogOperationBytes,
+                      tojson(res.transactions));
+        }
+        assert.docEq(writeConcern,
+                     res.transactions.lastCommittedTransaction.writeConcern,
+                     tojson(res.transactions));
+    }
+
+    // Initially the 'lastCommittedTransaction' section is not present.
+    let res = assert.commandWorked(primary.adminCommand({serverStatus: 1}));
+    assert(res.hasOwnProperty("transactions"), tojson(res));
+    assert(!res.transactions.hasOwnProperty("lastCommittedTransaction"), tojson(res));
+
+    // Start a transaction. The 'lastCommittedTransaction' section is not updated until the
+    // transaction commits.
+    session.startTransaction();
+    assert.commandWorked(sessionColl.insert({}));
+    res = assert.commandWorked(primary.adminCommand({serverStatus: 1}));
+    assert(res.hasOwnProperty("transactions"), tojson(res));
+    assert(!res.transactions.hasOwnProperty("lastCommittedTransaction"), tojson(res));
+
+    // Commit the transaction. The 'lastCommittedTransaction' section should be updated.
+    assert.commandWorked(session.commitTransaction_forTesting());
+    checkLastCommittedTransaction(1, {});
+
+    // Run a transaction with multiple write operations.
+    session.startTransaction();
+    assert.commandWorked(sessionColl.insert({}));
+    assert.commandWorked(sessionColl.insert({}));
+    assert.commandWorked(session.commitTransaction_forTesting());
+    checkLastCommittedTransaction(2, {});
+
+    // Run a read-only transaction.
+    session.startTransaction();
+    sessionColl.findOne();
+    assert.commandWorked(session.commitTransaction_forTesting());
+    checkLastCommittedTransaction(0, {});
+
+    // Run a transaction with non-default writeConcern.
+    session.startTransaction({writeConcern: {w: 1}});
+    assert.commandWorked(sessionColl.insert({}));
+    assert.commandWorked(session.commitTransaction_forTesting());
+    checkLastCommittedTransaction(1, {w: 1, wtimeout: 0});
+
+    // Run a read-only transaction with non-default writeConcern.
+    session.startTransaction({writeConcern: {w: "majority"}});
+    sessionColl.findOne();
+    assert.commandWorked(session.commitTransaction_forTesting());
+    checkLastCommittedTransaction(0, {w: "majority", wtimeout: 0});
+
+    session.endSession();
+    rst.stopSet();
+}());
diff --git a/src/mongo/db/server_transactions_metrics.cpp b/src/mongo/db/server_transactions_metrics.cpp
index 376425f1707..da5f2b8a112 100644
--- a/src/mongo/db/server_transactions_metrics.cpp
+++ b/src/mongo/db/server_transactions_metrics.cpp
@@ -113,6 +113,18 @@ void ServerTransactionsMetrics::incrementTotalCommitted() {
     _totalCommitted.fetchAndAdd(1);
 }
 
+void ServerTransactionsMetrics::updateLastTransaction(size_t operationCount,
+                                                      size_t oplogOperationBytes,
+                                                      BSONObj writeConcern) {
+    stdx::lock_guard<stdx::mutex> lg(_mutex);
+    if (!_lastCommittedTransaction) {
+        _lastCommittedTransaction = LastCommittedTransaction();
+    }
+    _lastCommittedTransaction->setOperationCount(operationCount);
+    _lastCommittedTransaction->setOplogOperationBytes(oplogOperationBytes);
+    _lastCommittedTransaction->setWriteConcern(std::move(writeConcern));
+}
+
 void ServerTransactionsMetrics::updateStats(TransactionsStats* stats) {
     stats->setCurrentActive(_currentActive.load());
     stats->setCurrentInactive(_currentInactive.load());
@@ -120,6 +132,11 @@ void ServerTransactionsMetrics::updateStats(TransactionsStats* stats) {
     stats->setTotalAborted(_totalAborted.load());
     stats->setTotalCommitted(_totalCommitted.load());
     stats->setTotalStarted(_totalStarted.load());
+
+    stdx::lock_guard<stdx::mutex> lg(_mutex);
+    if (_lastCommittedTransaction) {
+        stats->setLastCommittedTransaction(*_lastCommittedTransaction);
+    }
 }
 
 class TransactionsSSS : public ServerStatusSection {
diff --git a/src/mongo/db/server_transactions_metrics.h b/src/mongo/db/server_transactions_metrics.h
index b2020242aaa..02f397cde9e 100644
--- a/src/mongo/db/server_transactions_metrics.h
+++ b/src/mongo/db/server_transactions_metrics.h
@@ -69,6 +69,10 @@ public:
     unsigned long long getTotalCommitted() const;
     void incrementTotalCommitted();
 
+    void updateLastTransaction(size_t operationCount,
+                               size_t oplogOperationBytes,
+                               BSONObj writeConcern);
+
     /**
      * Appends the accumulated stats to a transactions stats object.
      */
@@ -92,6 +96,11 @@ private:
 
     // The total number of multi-document transaction commits.
     AtomicUInt64 _totalCommitted{0};
+
+    // Protects member variables below.
+    mutable stdx::mutex _mutex;
+
+    boost::optional<LastCommittedTransaction> _lastCommittedTransaction;
 };
 
 }  // namespace mongo
diff --git a/src/mongo/db/session.cpp b/src/mongo/db/session.cpp
index 47727848aae..d30ba490fae 100644
--- a/src/mongo/db/session.cpp
+++ b/src/mongo/db/session.cpp
@@ -1074,23 +1074,24 @@ void Session::commitTransaction(OperationContext* opCtx) {
 
 void Session::_commitTransaction(stdx::unique_lock<stdx::mutex> lk, OperationContext* opCtx) {
     invariant(_txnState == MultiDocumentTransactionState::kInProgress);
-    const bool isMultiDocumentTransaction = _txnState == MultiDocumentTransactionState::kInProgress;
-    if (isMultiDocumentTransaction) {
-        // We need to unlock the session to run the opObserver onTransactionCommit, which calls back
-        // into the session.
-        lk.unlock();
-        auto opObserver = opCtx->getServiceContext()->getOpObserver();
-        invariant(opObserver);
-        opObserver->onTransactionCommit(opCtx);
-        lk.lock();
-        // It's possible some other thread aborted the transaction (e.g. through killSession) while
-        // the opObserver was running.  If that happened, the commit should be reported as failed.
-        uassert(ErrorCodes::NoSuchTransaction,
-                str::stream() << "Transaction " << opCtx->getTxnNumber()
-                              << " aborted while attempting to commit",
-                _txnState == MultiDocumentTransactionState::kInProgress &&
-                    _activeTxnNumber == opCtx->getTxnNumber());
-    }
+    const size_t operationCount = _transactionOperations.size();
+    const size_t oplogOperationBytes = _transactionOperationBytes;
+
+    // We need to unlock the session to run the opObserver onTransactionCommit, which calls back
+    // into the session.
+    lk.unlock();
+    auto opObserver = opCtx->getServiceContext()->getOpObserver();
+    invariant(opObserver);
+    opObserver->onTransactionCommit(opCtx);
+    lk.lock();
+
+    // It's possible some other thread aborted the transaction (e.g. through killSession) while the
+    // opObserver was running.  If that happened, the commit should be reported as failed.
+    uassert(ErrorCodes::NoSuchTransaction,
+            str::stream() << "Transaction " << opCtx->getTxnNumber()
+                          << " aborted while attempting to commit",
+            _txnState == MultiDocumentTransactionState::kInProgress &&
+                _activeTxnNumber == opCtx->getTxnNumber());
     _txnState = MultiDocumentTransactionState::kCommitting;
     bool committed = false;
     ON_BLOCK_EXIT([this, &committed, opCtx]() {
@@ -1158,7 +1159,11 @@ void Session::_commitTransaction(stdx::unique_lock<stdx::mutex> lk, OperationCon
     // inactive.
     ServerTransactionsMetrics::get(opCtx)->incrementTotalCommitted();
     ServerTransactionsMetrics::get(opCtx)->decrementCurrentOpen();
-    ServerTransactionsMetrics::get(getGlobalServiceContext())->decrementCurrentActive();
+    ServerTransactionsMetrics::get(opCtx)->decrementCurrentActive();
+    ServerTransactionsMetrics::get(opCtx)->updateLastTransaction(
+        operationCount,
+        oplogOperationBytes,
+        opCtx->getWriteConcern().usedDefault ? BSONObj() : opCtx->getWriteConcern().toBSON());
     auto curTime = curTimeMicros64();
     Top::get(getGlobalServiceContext())
         .incrementGlobalTransactionLatencyStats(_singleTransactionStats.getDuration(curTime));
diff --git a/src/mongo/db/transactions_stats.idl b/src/mongo/db/transactions_stats.idl
index b47f49d2b6b..23f0000bf3d 100644
--- a/src/mongo/db/transactions_stats.idl
+++ b/src/mongo/db/transactions_stats.idl
@@ -38,6 +38,20 @@ imports:
 
 structs:
 
+  LastCommittedTransaction:
+    description: "A struct representing the server status subsection on
+                  the last committed transaction"
+    strict: true
+    fields:
+      operationCount:
+        type: long
+        default: 0
+      oplogOperationBytes:
+        type: long
+        default: 0
+      writeConcern:
+        type: object
+
   TransactionsStats:
     description: "A struct representing the section of the server status
                   command with information about transactions"
@@ -70,3 +84,6 @@ structs:
       totalStarted:
         type: long
         default: 0
+      lastCommittedTransaction:
+        type: LastCommittedTransaction
+        optional: true