Privy: Transaction-Wallet System

Role: Back-End Engineer
Duration: 9 months

Background

In today’s data driven-landscape, It’s ironic for a digital-first company to struggle with managing its transactional data (including users data)— especially when the data is critical to shaping future business decisions.

A core issue we faced was that the transactional data was scattered across multiple systems, each with its workflow, schema, and logic. This siloed operations made it difficult to consistently track revenue and cost across units and prevented us from forming a cohesive view of user behavior and transactions.

To address this, we introduced the concept of an centralized data ecosystem—an internal “tribe” responsible for transforming disparate data sources into a unified format that aligns with financial reporting requirements and supports accurate business evaluation.

Core: Transaction & Wallet Services

Transaction-Wallet is a distributed financial transactions and ledger ecosystem built to orchestrate balance actions (e.g., top-up, book, usage, cancel, transfer). Act as single source of truth for financial transactions and record cost-revenue events to an internal ERP system. The platform consists of two core services:

Transaction Service – Acts as a data aggregator, handling real-time balance actions and routing transactions to the ERP system.
Wallet Service – Serves as the centralized ledger, maintaining accurate, auditable transactions of all user balances and usage operations.

Designed with event-driven principles and optimized for high availability, low latency, and strong consistency across services.

Tech Stack

Languages: Golang
Database: PostgreSQL, Google Firestore
Caching & Messaging: Redis, Google Pub/Sub
CI/CD & Containerization: GitLab CI, Docker, Kubernetes
APM: Datadog

Challenges

Develop system that handle 10,000+ data volumes every 15 minutes with consistent performance under heavy traffic.
Design flexible schemas to accommodate personal, enterprise hierarchy, and reseller-level wallet business models.
Require strict adherence to CAP principles—balancing consistency, availability, and partition tolerance in a high-concurrency environment.

Contributions

Built both services from scratch, deeply involved in planning, system design, API contract, technical flow, and implementation.
Implemented a sophisticated retries and deadline mechanism for balance updates to the Wallet service. This prevents infinite loops in case of persistent issues while ensuring system resiliency.
Achieved high consistency in concurrent usage actions by leveraging Redis-based distributed locking, effectively eliminating race conditions.
Implemented message-driven auto-action request using worker schedulers and Redis as a message broker to automate a usage action.
Engineered a user subscription transactions workflow including checkout-settlement, book-activation, and expired process through payment and platform service.
Developed a Enterprise Account (EA) wallet management system for assign, un-assign, top-up, add-on, and extension scenarios.
Developed allocate balances feature with an optimistic lock approach instead of an exclusive lock to reduce blocking and improve concurrency in Wallet service.
Developed a mass migration of personal balances (transfer L1 to L2) feature
Engineered bulk dormant balance processing for EMAC (Enterprise, Merchant, Application, Channel) use cases.
Designed reseller schemas on both EMAC and Personal wallet.

Capabilities Demonstrated

Proficient in building and scaling distributed financial systems with strong transactional guarantees. Achieved over 70 requests per second (RPS) throughput, with 95% of 300,000 transactions completing in under 0.7 seconds and zero transaction failures during peak-hour performance testing.
Deep experience in message-driven architecture and real-time processing.
Skilled in implementing database indexing, distributed locks, data integrity, and performance optimizations for high-throughput system.
Able to responsibly maintain full-lifecycle development—from initial concept to production-ready deployment.

Architecture

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