What is writebehind?

WriteBehind is a tool that automatically syncs data from Redis, a fast in-memory data store, into a slower but more permanent database like MySQL. The core benefit is simple: you write data once to Redis for speed, and it shows up in your database automatically without you writing any extra code to handle the transfer. Here is how it works under the hood. When you save data to Redis (like a person's profile), a trigger captures that change instantly. Instead of sending it straight to the database, which would slow Redis down, it drops the change into a temporary internal queue called a Redis Stream. A background process then reads from this queue and writes the data to your target database. This ensures Redis stays fast while still reliably getting your data into permanent storage. This is useful for developers building apps that need both high speed and data permanence. For example, an e-commerce app might use Redis to quickly handle thousands of shopping cart updates per second, but still need those orders saved in a traditional database for analytics and reporting. It also gives you control: you can choose to save something in Redis without replicating it to the database, or request a confirmation when the data successfully reaches its final destination. A notable tradeoff the project addresses is data consistency. By default, it guarantees data will be written to the target database "at least once," meaning if something goes wrong, a piece of data might be written twice. However, it offers an advanced "exactly once" mode for SQL databases to prevent any duplicates. To prevent data loss entirely if Redis crashes, the project strongly recommends running Redis with replication or persistence features turned on.