Redis transaction mechanism implementation process and principle, and use transaction mechanism to prevent inventory oversold

One 、Redis The process and principle of transaction implementation

First step ： Observation data

Before the client modifies the data , First use watch Command to observe the data to be modified , This step is equivalent to recording the version number of the data

The second step ： Open transaction

Use multi Order to start a transaction .

After opening the transaction , All commands will not be sent immediately to Redis, Instead, cache it locally on the client , It's not really going to be implemented , Until the execution of exec When you order a transaction to be committed , The client will send these commands to Redis To carry out .

The third step ：Redis Carry out orders

Client side usage exec Commit transaction ,Redis Received client exec After the command , The version number of the data will be compared first , If the version number is the same , Will execute all commands submitted by the client .

If the current version number and are watch The version number is inconsistent , Then all commands in the transaction submitted by the client will not be executed , It is equivalent to the transaction execution failure .

Two 、 Actual operation

Summarize the process ： Use watch Monitoring data , Then start the transaction , Do business processing , Submission of orders .

 

notes ： Under what circumstances , There will be inconsistent version numbers ？

For example, client A Open transaction , But it hasn't been implemented yet exec Submit , At this time, the client A Yes Redis The commands of are cached on the client A On , It has not been submitted in batch to Redis Carry out orders , At this time, the client B Write the data , Then the version number of this data will change , At this time , client A perform exec command , The version number will be inconsistent , Causes the client to A The problem that all commands under this transaction fail to execute .

3、 ... and 、PHP Pseudo code , Realize the prevention of commodity oversold

 

Four 、 explain

Redis adopt watch And multi Realize the problem of preventing oversold , Its essence is divided into two parts ：

The first part is watch, The second part is from multi To exec All the orders of .

When the client watch command ,Redis Start monitoring data , Get the current version number of the data

When the client exec command ,Redis First, check whether the current version number of the data is consistent with the version number at the beginning of monitoring , If it is consistent, we will start from multi To exec All commands of are executed , otherwise multi To exec All commands of are not executed .