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A matching engine is the core component of an order-book trading system.

Its job is to receive buy and sell orders, compare prices, determine execution priority, and generate trades as quickly and accurately as possible.

A typical matching process looks like this:

1. The system receives a new order
2. Basic risk and balance checks are completed
3. The order enters the matching queue
4. The engine searches the opposite side of the order book
5. Compatible orders are matched
6. Trade records and balance updates are generated
7. Market data is published through WebSocket

Most exchanges use **price-time priority**:

* Better prices are matched first
* Orders at the same price are matched by arrival time

For example, a market buy order will consume the lowest available sell orders first. If the quantity is large, it may match across several price levels.

A reliable matching engine also needs:

* High-performance in-memory order books
* Deterministic order processing
* Unique sequence numbers
* Partial-fill support
* Order cancellation and modification
* Persistent event logs
* Real-time market-data distribution
* Recovery and replay mechanisms
* Pre-trade and post-trade risk controls

The biggest technical challenge is not only speed.

The engine must also guarantee that orders are processed in the correct sequence, trades are not duplicated, balances remain consistent, and the system can recover after a failure.

In trading infrastructure, performance matters—but correctness comes first.

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How a Matching Engine Works