mysql.connector SELECT查询是同时运行还是顺序运行？

Question

I'm currently using mysql.connector in a python Flask project and, after users enter their information, the following query is executed:

"SELECT first, last, email, {} FROM {} WHERE {} <= {} AND ispaired IS NULL".format(key, db, class_data[key], key)

It would pose a problem if this query was executed in 2 threads concurrently, and returned the same row in both threads. I was wondering if there was a way to prevent SELECT mysql queries from executing concurrently, or if this was already the default behavior of mysql.connector ? For additional information, all mysql.connector queries are executed after being authenticated with the same account credentials.

Answer 1

It is hard to say from your description, but if you're using Flask, you're most probably using (or will use in production) multiple processes, and you probably have a connection pool (ie multiple connections) in each process. So while each connection is executing queries sequentially, this query can be ran concurrently by multiple connections at the same time.

To prevent your application from obtaining the same row at the same time while handling different requests, you should use transactions and techniques like SELECT FOR UPDATE . The exact solution depends on your exact use case.