raj mehroliya

Backend Engineer · Distributed Systems · Payments

Ship it. Then sit with it. That’s where the craft sharpens.

I build backend systems where correctness is the feature — payments, concurrency, dispatch, and multi-tenant infrastructure running in production.

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Shipped in production

5
Payment providers
75%
API cost reduction
20%
Reduction in payment inconsistencies
3+ yrs
Production engineering

Currently

Software Development Engineer II at Togopool

Promoted to SDE II in January 2026. Own distributed-systems features across the ride lifecycle: concurrency-safe booking, routing safety, and multi-region scheduling.

Full experience →

Selected Work

All projects →

Case studies, not screenshots — the problem, the architecture, and the trade-offs behind each system.

Multi-Tenant Wallet & Payments Infrastructure

From debugging silent payment failures to architecting a reconciliation-first wallet system across five payment providers.

  • Node.js
  • Express.js
  • MySQL
  • Redis
  • Stripe
  • +4 more
Read case study →

Driver Promotions with Fraud Detection

An incentive system designed on the assumption that users will try to game it — with geofence integrity enforced in SQL.

  • Node.js
  • MySQL
  • Spatial SQL
  • Redis
Read case study →

Architecture Lab

All entries →

Step-through walkthroughs of systems I've run in production — the real flows, the failure modes, and the fixes they forced. One of them you can attack yourself.

InteractiveSeat locking

Try to break the seat lock

Two phones, eight seats, one lock — and both phones are yours. Take the same seat twice, let a hold expire, pay with a dead token. Every rejection is a defense that exists in production for a reason.

Open the simulator →

Distributed Seat Locking

Exactly one winner per seat — enforced atomically, verified again at payment, and correct even when holds expire mid-flow.

8-step walkthrough

Wallet Transaction Flow

Money left the passenger and never reached the driver — the incident that turned a wallet into a ledger.

5-step walkthrough

Route Computation at 25% of the Bill

Every fare estimate was a paid API call. Cutting the bill by 75% meant asking a cheaper question, asking it less often, and still answering when the provider didn't.

5-step walkthrough

Driver Dispatch Under Timeouts

A search problem with a clock on it — expanding rings, batched offers, and a retry loop for when the answer is 'not yet' rather than 'no'.

8-step walkthrough

Stack

Languages

  • JavaScript
  • TypeScript
  • Python
  • SQL

Backend

  • Node.js
  • Express.js

Databases

  • MySQL
  • MongoDB
  • Redis

Cloud

  • AWS EC2
  • AWS S3
  • AWS RDS

Tools

  • Docker
  • Git