Traditional methods of communication between terminals, such as Global Variables or local CSV files, often fall short when dealing with high-frequency data or complex relational structures. SQLite provides a serverless, zero-configuration database engine that allows for structured data storage, ensuring that every trade, modification, and balance update is logged and accessible by any authorized terminal in the network.

## 2. Why SQLite is the Best Choice ()

MQL5 provides native support for SQLite, making it an incredibly efficient tool for developers. The primary advantages include:

Zero Configuration: Unlike SQL Server or MySQL, SQLite does not require a separate server process. The entire database is stored in a single file on your hard drive.

Speed: It is optimized for local read/write operations, which is crucial for trading environments where milliseconds matter.

ACID Compliance: It ensures that database transactions are processed reliably, preventing data corruption during sudden system crashes or power failures.

Portability: The database file can be easily moved or backed up, making it ideal for traders who use Virtual Private Servers (VPS).

## 3. Designing the Database Schema ()

Accounts Table: To store account numbers, broker names, and leverage settings.

Trades Table: To log every open position, including ticket numbers, entry prices, and stop-loss levels.

History Table: To keep a record of closed trades for performance analysis.

By using structured tables, we can perform complex SQL queries, such as calculating the total exposure across all accounts for a specific currency pair (e.g., EURUSD) with a single command.

## 4. The Synchronization Logic: Step-by-Step ()

The core of our system is a "Synchronization Engine" built within an Expert Advisor. The logic follows a continuous loop:

Step A: Data Extraction

The EA uses the Position Get Double and Position Get Integer functions to scan the current terminal's state. It gathers information such as the current profit, swap, and volume for every open position.

Step B: Writing to the Centralized Database

Once the data is gathered, the EA opens a connection to the shared SQLite file. It uses the DatabaseExecute function to run "INSERT" or "UPDATE" queries. This ensures that the centralized file always reflects the most recent state of the local terminal.

Step C: Cross-Terminal Reading

Other terminals running the same synchronization EA will periodically "SELECT" data from the database. If Terminal A opens a trade, Terminal B will see that trade in the database within milliseconds and can adjust its own risk management logic accordingly.

##5.Handling Multi-Terminal Conflicts()

One common issue in centralized systems is "Database Locking." This happens when two terminals try to write to the same SQLite file at exactly the same time. To solve this, we implement a "Retry Logic" in MQL5. If the database returns a "BUSY" error, the EA will wait for a few microseconds and try again. This ensures that no data is lost even in a busy multi-account environment.

##6. Performance Optimization and Maintenance()

As the number of trades grows, the database file can become large. To maintain peak performance, we recommend:

Indexing: Create indexes on columns like "Ticket" and "AccountNumber" to speed up search queries.

Vacuuming: Regularly use the VACUUM command to defragment the database file and reduce its size.

Asynchronous Operations: While MQL5 is single-threaded, we can optimize our SQL queries to be as short as possible to avoid freezing the terminal's main thread.

//+------------------------------------------------------------------+
//|                                     PortfolioSync_SQLite.mq5      |
//|                                  Copyright 2026, Trading Expert  |
//+------------------------------------------------------------------+
#property copyright "Copyright 2026"
#property link      "https://www.mql5.com"
#property version   "1.00"
#property strict
// Global handle for the database

int db_handle = INVALID_HANDLE;
//+------------------------------------------------------------------+

//| Expert initialization function                                   |

//+------------------------------------------------------------------+

int OnInit()

{

   // Open or create the centralized database file

   db_handle = DatabaseOpen("CentralPortfolio.db", DATABASE_OPEN_READWRITE | DATABASE_OPEN_CREATE | DATABASE_OPEN_COMMON);

  

   if(db_handle == INVALID_HANDLE)

   {

      Print("Error: Failed to open database. Code: ", GetLastError());

      return(INIT_FAILED);

   }
   // Create a table for account synchronization if it doesn't exist

   string query = "CREATE TABLE IF NOT EXISTS Portfolio (ID INTEGER PRIMARY KEY, Account INTEGER, Equity REAL, Profit REAL);";

   if(!DatabaseExecute(db_handle, query))

   {

      Print("Error creating table: ", GetLastError());

      DatabaseClose(db_handle);

      return(INIT_FAILED);

   }
   Print("Database initialized successfully.");

   return(INIT_SUCCEEDED);

}
//+------------------------------------------------------------------+

//| Expert deinitialization function                                 |

//+------------------------------------------------------------------+

void OnDeinit(const int reason)

{

   if(db_handle != INVALID_HANDLE)

   {

      DatabaseClose(db_handle);

      Print("Database connection closed.");

   }

}
//+------------------------------------------------------------------+

//| Expert tick function                                             |

//+------------------------------------------------------------------+

void OnTick()

{

   double equity = AccountInfoDouble(ACCOUNT_EQUITY);

   double profit = AccountInfoDouble(ACCOUNT_PROFIT);

   long account_id = AccountInfoInteger(ACCOUNT_LOGIN);
   // Update account info in the centralized database

   string query = StringFormat("INSERT OR REPLACE INTO Portfolio (ID, Account, Equity, Profit) VALUES (1, %lld, %f, %f);",

                               account_id, equity, profit);
   if(!DatabaseExecute(db_handle, query))

   {

      Print("Failed to update database: ", GetLastError());

   }

}