BidLock: Real-Time Bidding & Request Dispatch Engine

A high-performance DBMS project focused on transaction integrity, concurrency, and real-time architecture using a "Thick Database, Thin API" philosophy.

About The Project

BidLock is an advanced backend engine handling two major systems: a real-time auction bidding platform, and a geospatial ride dispatcher.

In modern applications, managing complex financial states and preventing race-conditions at the API level often leads to latency and double-spend bugs. BidLock solves this by delegating all critical financial computations, spatial queries, and concurrency controls directly to the PostgreSQL database layer.

By utilizing robust database features like FOR UPDATE SKIP LOCKED, complex trigger constraints, and strict SERIALIZABLE transaction bounds, the database natively guarantees that:

• Wallet balances never drop below zero.
• Submitted bids are never duplicated or overwritten unfairly.
• Thousands of concurrent riders and drivers can be matched with microsecond latency without race conditions.

The Node.js Express server acts as a lightweight conduit, simply streaming these database-triggered state changes directly to the React/HTML frontend via Redis pub-sub caching and WebSockets.

Architecture (ER Diagram)

erDiagram
    APP_USERS ||--o{ AUCTIONS : "wins"
    APP_USERS ||--o{ BIDS : "places"
    APP_USERS ||--o{ WALLET_HOLDS : "has"
    APP_USERS ||--o| ACTIVE_DRIVERS : "is a"
    APP_USERS ||--o{ RIDE_REQUESTS : "requests"
    
    AUCTIONS ||--o{ BIDS : "receives"
    AUCTIONS ||--o{ WALLET_HOLDS : "secures"
    
    BIDS ||--o{ WALLET_HOLDS : "requires"
    BIDS ||--o{ BID_AUDIT_LOG : "generates"
    
    ACTIVE_DRIVERS ||--o{ RIDE_REQUESTS : "serves"
    ACTIVE_DRIVERS ||--o{ MATCHING_LOG : "evaluated in"
    
    RIDE_REQUESTS ||--o{ MATCHING_LOG : "has"
    RIDE_REQUESTS ||--o{ RIDE_STATE_HISTORY : "tracks"

    APP_USERS {
        UUID id PK
        TEXT name
        NUMERIC wallet_balance
        TIMESTAMPTZ created_at
    }

    AUCTIONS {
        UUID id PK
        TEXT title
        TEXT status
        TIMESTAMPTZ start_at
        TIMESTAMPTZ end_at
        NUMERIC min_increment
        NUMERIC current_max_bid
        UUID current_winner_id FK
    }

    BIDS {
        UUID id PK
        UUID auction_id FK
        UUID bidder_id FK
        NUMERIC bid_amount
        BOOLEAN is_active
        TEXT idempotency_key
    }

    WALLET_HOLDS {
        UUID id PK
        UUID user_id FK
        UUID auction_id FK
        UUID bid_id FK
        NUMERIC hold_amount
        BOOLEAN released
    }

    BID_AUDIT_LOG {
        BIGSERIAL id PK
        UUID bid_id FK
        UUID auction_id FK
        TEXT event_type
        JSONB event_payload
    }

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Tech Stack

• API Layer: Node.js v20+, TypeScript, Express.js
• Database: PostgreSQL 16
• Spatial Expansion: PostGIS (for fast proximity calculation)
• High Concurrency: Redis & Socket.io for immediate real-time browser updates
• Security & Auth: JSON Web Tokens (JWT), Helmet.js, express-rate-limit
• Testing: Jest, Supertest
• Worker Management: PM2 (ecosystem.config.js)

Technical Requirements

• Node.js
• Docker Desktop (Using docker-compose configures Postgres + Redis natively).

Quick Start

1. Ensure Docker Desktop is up and running.
2. Initialize environment variables (copy .env.example -> .env).
3. Start the primary services:

   docker-compose up -d

4. Install node dependencies and trigger the built-in database setup/seed script:

   npm install
   npm run db:setup

5. Start the web server:

   npm run dev

6. Open your browser directly to http://localhost:3000/ to view the Live Socket interface!

Testing & Production

Running Tests: To run the automated integration test suite that verifies the JWT auth barriers and error handling, run:

npm test

Running in Production (PM2): To start the API and all background workers concurrently using PM2:

npx pm2 start ecosystem.config.js
npx pm2 logs

Automated Demonstrations

Because this is a server architecture project designed to withstand massive parallel loads, we package scripts to simulate heavy network use. With the npm run dev server active in one terminal, run these scripts in another terminal while watching your browser http://localhost:3000/ automatically populate in real-time.

• npm run demo:bid-race - Spams the auction server simultaneously with identical IDs to force Postgres into a Concurrency lock, proving only 1 bidder accurately walks away without overriding table data.
• npm run demo:driver-herd - Tests PostGIS GEOMETRY features to match the nearest GPS lat-long coordinates to a driver requesting a ride with SKIP LOCKED protection.