Redis message queue repeated consumption

A recent problem , Make a note of .

The last article said SpringBoot+Redis Implement simple publishing / subscribe

What happened

The short message module in our current project is adopted Redis For message queuing , The reason is that recently, some applications reported that when sending text messages , Occasionally, it is sent twice .

After investigation , It does exist , This is the processing before our research and development. The lock will be deleted after sending a text message , In this way, if the network fluctuates , It will be sent twice .

The details are as follows , We have two examples , Each instance is subscribed to topic, Each consumer will be notified when sending , Each instance acquires the lock , And then send a text message ; It was like this , After the producer sends , Consumers begin to consume The time consumed by the first instance is 18:10:024, Then do business processing , The completion time of sending SMS is 18:10:056（ Check the time through the log ）, Handled quickly , It can be processed in tens of milliseconds , Then delete the lock . The second example consumes time 18:10:244, At this time, the first instance has been processed , And remove the lock , So when the second instance tries to acquire the lock, it will succeed directly , Then the business processing is carried out , The completion time of resending the second SMS is 18:10:268. Therefore, it will occasionally send twice .

Find the problem and fix it , The main solution is to fail to acquire the lock for the second time .

Here, we modify it to obtain the lock after the business processing is completed , Do not delete locks directly , Instead, let it lapse over time , In this way, other instances will not succeed in obtaining locks during this period , Even if it is handled quickly for the first time , It will not be processed by two consumption .

Here we set the expiration time to 1 minute , Later, it can be adjusted according to the business situation .

summary

This time we also know , When doing business , It is not only necessary to lock and unlock , Also consider various situations ; When processing message queues , Repeated consumption is a common problem , This is an experience .

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