With high concurrency flash sale, how to ensure that Redis cache inventory is consistent with database inventory?

PHP Redis flash sale system inventory consistency solution

In the high concurrency flash sale scenario, how to ensure the consistency of Redis cache inventory and database inventory data is the key to system stability. This paper analyzes the flash sale process based on Redis atomic self-decreasing operation and proposes solutions to solve the possible "selling less" problem under high concurrency.

Common flash sale process: placing an order -> Redis inventory deduction -> Creating an order -> Paying successfully, updating the database. Although using Redis's decrBy method can quickly deduct inventory, under high concurrency, due to the non-atomic nature of Redis operations and database operations, it may cause problems. Multiple requests to deduct Redis inventory at the same time successfully, but the database operation partially failed due to concurrency or delay, and Redis inventory could not be retracted in time, resulting in "less selling". Even if the code rolls back the Redis inventory when create_order() fails, the rollback may also fail if the internal database operation create_order() does not have a transaction or lock mechanism.

Solution: Introduce message queue

To ensure atomicity, it is recommended to use a message queue. After the Redis inventory deduction is successful, the order information is placed in the message queue. The independent consumer process reads order information from the queue and then performs database order creation and inventory update operations. This solution ensures the atomicity of Redis inventory deductions and database operations, and will not affect the fallback of Redis inventory even if the database operation fails.

Key Improvements:

• Message queue ensures atomicity: decouples Redis operations and database operations to avoid concurrent conflicts.
• Database transaction: Database operations should be included in the transaction to ensure the atomicity of order creation and inventory updates.

Through the combination of message queues and database transactions, the problem of inconsistency between Redis and database inventory under high concurrency is effectively solved, and the stability and reliability of the flash sale system are improved.

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