Core/DBLayer:

- Implement DatabaseWorkerPool::DirectCommitTransaction for synchronous transaction execution (as opposed to asynchronous/enqueued).
- Add MySQL errno 1213 "Deadlock found when trying to get lock; try restarting transaction" handler. If 1213 is called the core will retry to directly execute the transaction a maximum of 5 times.

src/server/shared/Database/DatabaseWorkerPool.h

@@ -353,6 +353,30 @@ class DatabaseWorkerPool
             Enqueue(new TransactionTask(transaction));
         }
 
+        //! Directly executes a collection of one-way SQL operations (can be both adhoc and prepared). The order in which these operations
+        //! were appended to the transaction will be respected during execution.
+        void DirectCommitTransaction(SQLTransaction& transaction)
+        {
+            MySQLConnection* con = GetFreeConnection();
+            if (con->ExecuteTransaction(transaction))
+            {
+                con->Unlock();      // OK, operation succesful
+                return;
+            }
+            
+            if (con->GetLastError() == 1213)
+            {
+                uint8 loopBreaker = 5;  // Handle MySQL Errno 1213 without extending deadlock to the core itself
+                for (uint8 i = 0; i < loopBreaker; ++i)
+                {
+                    if (con->ExecuteTransaction(transaction))
+                        break;
+                }
+            }
+
+            con->Unlock();
+        }
+
         //! Method used to execute prepared statements in a diverse context.
         //! Will be wrapped in a transaction if valid object is present, otherwise executed standalone.
         void ExecuteOrAppend(SQLTransaction& trans, PreparedStatement* stmt)

src/server/shared/Database/MySQLConnection.cpp

@@ -369,6 +369,52 @@ void MySQLConnection::CommitTransaction()
     Execute("COMMIT");
 }
 
+bool MySQLConnection::ExecuteTransaction(SQLTransaction& transaction)
+{
+    std::queue<SQLElementData> &queries = transaction->m_queries;
+    if (queries.empty())
+        return false;
+
+    BeginTransaction();
+    while (!queries.empty())
+    {
+        SQLElementData data = queries.front();
+        switch (data.type)
+        {
+            case SQL_ELEMENT_PREPARED:
+            {
+                PreparedStatement* stmt = data.element.stmt;
+                ASSERT(stmt);
+                if (!Execute(stmt))
+                {
+                    sLog->outSQLDriver("[Warning] Transaction aborted. %u queries not executed.", (uint32)queries.size());
+                    RollbackTransaction();
+                    return false;
+                }
+                delete data.element.stmt;
+            }
+            break;
+            case SQL_ELEMENT_RAW:
+            {
+                const char* sql = data.element.query;
+                ASSERT(sql);
+                if (!Execute(sql))
+                {
+                    sLog->outSQLDriver("[Warning] Transaction aborted. %u queries not executed.", (uint32)queries.size());
+                    RollbackTransaction();
+                    return false;
+                }
+                free((void*)const_cast<char*>(sql));
+            }
+            break;
+        }
+        queries.pop();
+    }
+
+    CommitTransaction();
+    return true;
+}
+
 MySQLPreparedStatement* MySQLConnection::GetPreparedStatement(uint32 index)
 {
     ASSERT(index < m_stmts.size());
@@ -462,6 +508,9 @@ bool MySQLConnection::_HandleMySQLErrno(uint32 errNo)
             return _HandleMySQLErrno(lErrno);           // Call self (recursive)
         }
 
+        case 1213:      // "Deadlock found when trying to get lock; try restarting transaction"
+            return true;    // Implemented in TransactionTask::Execute and DatabaseWorkerPool<T>::DirectCommitTransaction
+
         // Query related errors - skip query
         case 1058:      // "Column count doesn't match value count"
         case 1062:      // "Duplicate entry '%s' for key '%d'"

src/server/shared/Database/MySQLConnection.h

@@ -18,6 +18,7 @@
 #include <ace/Activation_Queue.h>
 
 #include "DatabaseWorkerPool.h"
+#include "Transaction.h"
 #include "Util.h"
 
 #ifndef _MYSQLCONNECTION_H
@@ -91,10 +92,13 @@ class MySQLConnection
         void BeginTransaction();
         void RollbackTransaction();
         void CommitTransaction();
+        bool ExecuteTransaction(SQLTransaction& transaction);
 
         operator bool () const { return m_Mysql != NULL; }
         void Ping() { mysql_ping(m_Mysql); }
 
+        uint32 GetLastError() { return mysql_errno(m_Mysql); }
+
     protected:
         bool LockIfReady()
         {

src/server/shared/Database/Transaction.cpp

@@ -67,45 +67,16 @@ void Transaction::Cleanup()
 
 bool TransactionTask::Execute()
 {
-    std::queue<SQLElementData> &queries = m_trans->m_queries;
-    if (queries.empty())
-        return false;
+    if (m_conn->ExecuteTransaction(m_trans))
+        return true;
 
-    m_conn->BeginTransaction();
-    while (!queries.empty())
+    if (m_conn->GetLastError() == 1213)
     {
-        SQLElementData data = queries.front();
-        switch (data.type)
-        {
-            case SQL_ELEMENT_PREPARED:
-            {
-                PreparedStatement* stmt = data.element.stmt;
-                ASSERT(stmt);
-                if (!m_conn->Execute(stmt))
-                {
-                    sLog->outSQLDriver("[Warning] Transaction aborted. %u queries not executed.", (uint32)queries.size());
-                    m_conn->RollbackTransaction();
-                    return false;
-                }
-                delete data.element.stmt;
-            }
-            break;
-            case SQL_ELEMENT_RAW:
-            {
-                const char* sql = data.element.query;
-                ASSERT(sql);
-                if (!m_conn->Execute(sql))
-                {
-                    sLog->outSQLDriver("[Warning] Transaction aborted. %u queries not executed.", (uint32)queries.size());
-                    m_conn->RollbackTransaction();
-                    return false;
-                }
-                free((void*)const_cast<char*>(sql));
-            }
-            break;
-        }
-        queries.pop();
+        uint8 loopBreaker = 5;  // Handle MySQL Errno 1213 without extending deadlock to the core itself
+        for (uint8 i = 0; i < loopBreaker; ++i)
+            if (m_conn->ExecuteTransaction(m_trans))
+                return true;
     }
-    m_conn->CommitTransaction();
-    return true;
+
+    return false;
 }

src/server/shared/Database/Transaction.h

@@ -27,6 +27,8 @@ class PreparedStatement;
 class Transaction
 {
     friend class TransactionTask;
+    friend class MySQLConnection;
+
     public:
         Transaction() {}
         ~Transaction() { Cleanup(); }
@@ -49,7 +51,7 @@ class TransactionTask : public SQLOperation
 {
     template <class T> friend class DatabaseWorkerPool;
     friend class DatabaseWorker;
-
+    
     public:
         TransactionTask(SQLTransaction trans) : m_trans(trans) {} ;
         ~TransactionTask(){};