CONNECTION POOL FOR POSTGRESQL USING PQXX (C++)

This is a connection pool implementation for managing PostgreSQL database connections using the pqxx library in C++. It is designed to efficiently manage a pool of database connections, reducing the overhead of repeatedly opening and closing connections. The pool supports prepared statements, connection limits, timeouts, and automatic cleanup of idle connections.

FEATURES:

• Connection reuse to minimize database connection overhead
• Prepared statement support during connection initialization
• Configurable minimum and maximum connection limits
• Timeout handling for connection acquisition
• Automatic cleanup of idle connections (30-minute threshold)
• Thread-safe operations using mutexes and condition variables
• Connection validation when retrieving from pool
• Retry mechanism for initial connection attempts

USAGE:

• Include the connection pool header in your project
• Link against pqxx and required PostgreSQL libraries
• Create a ConnectionPool instance with appropriate parameters
• Use get_connection() to obtain a connection guard
• Execute database operations through the connection guard
• The connection is automatically returned to the pool when the guard goes out of scope

CONFIGURATION PARAMETERS:

• Connection string (format: "dbname=... user=... host=... port=... password=...")
• Initial connection count
• Timeout duration for acquiring connections
• List of prepared statements (name/SQL pairs)
• Minimum connections (default: 1)
• Maximum connections (default: 4)
• Idle disconnect timeout in seconds (default: 60)

EXCEPTIONS:

• pqxx::broken_connection: Thrown when connection attempts fail during pool initialization or expansion
• std::runtime_error: Thrown when retrieving a closed connection from the pool

DEPENDENCIES:

• pqxx library (7.7+ recommended)
• C++17 or newer
• PostgreSQL client libraries
• Thread support (pthreads or equivalent)

EXAMPLE USAGE:

try {
    std::vector<Statement> prep = {{"find_user", "SELECT * FROM users WHERE id = $1"}};
    ConnectionPool pool(conn_str, 2, std::chrono::seconds(5), prep);
    
    auto conn = pool.get_connection();
    pqxx::work txn(*conn);
    auto result = txn.exec_prepared("find_user", 123);
    txn.commit();
}
catch (const std::exception &e) {
    // Handle exceptions
}

NOTES:

• The pool is thread-safe and can be used in multi-threaded environments
• Connections are returned to the pool automatically via RAII (ConnectionGuard destructor)
• Cleanup thread runs every 5 minutes to remove connections idle for more than 30 minutes
• Failed connection attempts during pool creation will retry 5 times per connection
• The pool maintains at least the minimum number of connections specified

BUILDING:

Ensure proper linking with pqxx and PostgreSQL libraries. Compile with C++17 support and thread-safe flags.

LIMITATIONS:

• Currently PostgreSQL-specific due to pqxx dependency
• Connection validation only occurs when checking out from pool
• Prepared statements must be redefined if connections are recreated