Redis 4.x Cookbook

How it works...

Overselling is often a headache for seckilling application design. The reason why the overselling happens is that there was a race condition at the time you retrieved the counter; the number might be valid for the business scenario, but before you decreased the counter, the counter may have been modified by other requests. In our example, we use a Redis transaction to avoid such a situation.

First, we call a WATCH command on the key to set a flag indicating if the key has been changed before the EXEC command; if so, we just discard the whole transaction. Then, we get the value of the counter.

Second, we start a transaction by calling the MULTI command, and if the counter is an invalid value, the transaction is stopped directly ...