Steps to update data to database and cache

Cache strategy: Cache aside

(1) Read request

The application first determines whether there is data in the cache. If the cache hits, it returns the data directly; if the cache does not hit, it queries the data from the database, writes it to the cache, and returns the data.

(2) Write request

Update the database first, then delete the data from the cache.

Question:

Why not just write back the data when writing the request?

In a concurrent scenario, data inconsistency may be found.For example, in the case of a write request, the database is updated first, and then the cache is updated. Request 1 first writes data 18 to the database, but the cache has not been updated. At this time, request 2 writes data 20 to the database, and the update cache data is 20. At this time, request 1 is updated again.Cache data, which will result in inconsistent data when the database data is 20 and the cached data is 18.