Ticketing & reservations
SmartQueue
High-traffic booking and payment engine
A booking and payment engine built to survive on-sale spikes, with no double-bookings under concurrent load, and no revenue lost between reservation and payment.
This example comes from the technical delivery experience behind AussieSync. It does not necessarily represent a project contracted directly through AussieSync.
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01 Problem
Concurrent demand for the same slot produces double-bookings, and payment failures silently lose revenue.
- Hundreds of users hitting one release window raced for the same inventory.
- A naive check-then-write let two bookings pass validation microseconds apart.
- Payment gateway timeouts left orders in limbo: charged but unconfirmed, or the reverse.
- Abandoned checkouts held inventory indefinitely, starving genuine buyers.
02 The solution
Redis-backed reservation locks with TTL, idempotent payment flows, and an event-driven confirmation pipeline.
- A short-lived distributed lock makes a slot exclusively held while checkout proceeds.
- Holds carry a TTL, so an abandoned cart auto-releases the inventory instead of stranding it.
- Reservation, payment and ticket issuance are decoupled stages on an event queue.
- Payment operations are idempotent, so a gateway retry cannot charge twice.
- Each stage is separately retryable, so a downstream failure never voids a valid booking.
03 Technical approach
Every choice earns its place.
- NestJSBooking and payment API with a typed, testable service boundary.
- PostgreSQLAuthoritative inventory and order records.
- RedisReservation locks with TTL, the mechanism preventing double-booking.
- Event queueDecouples reservation from payment from issuance.
04 Outcome
Zero double-bookings under load, with reliable revenue capture and inventory that releases itself.
- Zerodouble-bookings under concurrent load
- Reliablerevenue capture through gateway failures
- Auto-releasedholds recover abandoned-cart inventory