Merge pull request #2012 from Expensify/john-log-open-transactions

Handle open transactions monitoring on nodes

sqlitecluster/SQLite.cpp

@@ -401,7 +401,10 @@ bool SQLite::beginTransaction(TRANSACTION_TYPE type) {
     // Reset before the query, as it's possible the query sets these.
     _autoRolledBack = false;
 
-    SINFO("[concurrent] Beginning transaction");
+    // We actively track transaction counts incrementing and decrementing to log the number of active open transactions at any given moment.
+    _sharedData.openTransactionCount++;
+
+    SINFO("[concurrent] Beginning transaction - open transaction count: " << (_sharedData.openTransactionCount));
     uint64_t before = STimeNow();
     _insideTransaction = !SQuery(_db, "starting db transaction", "BEGIN CONCURRENT");
 
@@ -805,6 +808,8 @@ int SQLite::commit(const string& description, function<void()>* preCheckpointCal
         _mutexLocked = false;
         _queryCache.clear();
 
+        _sharedData.openTransactionCount--;
+
         if (preCheckpointCallback != nullptr) {
             (*preCheckpointCallback)();
         }
@@ -860,6 +865,8 @@ void SQLite::rollback() {
             _rollbackElapsed += STimeNow() - before;
         }
 
+        _sharedData.openTransactionCount--;
+
         // Finally done with this.
         _insideTransaction = false;
         _uncommittedHash.clear();
@@ -1185,6 +1192,7 @@ string SQLite::getLastConflictTable() const {
 SQLite::SharedData::SharedData() :
 nextJournalCount(0),
 _commitEnabled(true),
+openTransactionCount(0),
 _commitLockTimer("commit lock timer", {
     {"EXCLUSIVE", chrono::steady_clock::duration::zero()},
     {"SHARED", chrono::steady_clock::duration::zero()},

sqlitecluster/SQLite.h

@@ -323,6 +323,9 @@ class SQLite {
         // If set to false, this prevents any thread from being able to commit to the DB.
         atomic<bool> _commitEnabled;
 
+        // This variable is used to monitor the number of open transactions on the whole server.
+        atomic<int64_t> openTransactionCount;
+
         SPerformanceTimer _commitLockTimer;
 
         // We use this flag to prevent to threads running checkpoints t the same time.