What is the data exchange mechanism between Redis memory and disk?

Redis persistence mainly uses RDB and AOF. RDB regularly creates snapshots of memory data to disk, which has a fast recovery speed, but has a high risk of data loss; AOF records all write operations to ensure data integrity, but will affect performance and cause log files to grow. The two can be mixed, taking into account data security and performance.

To put it bluntly, data exchange between Redis memory and disk is persistence. This thing seems simple, but it actually makes a lot of tricks. I was in trouble back then. Simply put, Redis mainly relies on two ways to "move" memory data to disk: RDB snapshots and AOF logs.

Let’s talk about RDB first. It's like taking a photo of Redis, copying the entire memory data to disk regularly. This method is simple and crude, and it is quick to recover data, but the disadvantages are also obvious: the risk of data loss is relatively high. If you happen to have Redis hangs between two snapshots, the data in the middle will be gone. Therefore, RDB is suitable for scenarios where data consistency requirements are not as high as possible, such as some statistics.

Look at AOF again. This guy is more like a diary, recording every write operation. In this way, even if Redis is hung, the data can be restored based on the log. Data security is much higher than RDB, but writing logs will affect performance, and log files will become larger and larger, making it troublesome to manage. Therefore, AOF is suitable for scenarios with relatively high requirements for data integrity, such as e-commerce order systems.

Of course, these two methods can also be used in a mixed manner. It’s like taking photos and writing diaries, you must grab both hands and be hard on both hands. This ensures data security and takes into account performance. But don't be too happy too early, there is also knowledge in the middle. For example, after the AOF log file is too large, how to rewrite and configure appropriate strategies need to be carefully considered.

I used to use RDB in a project, but the server suddenly went down and lost several hours of data. I was almost fired by my boss. Later, I learned from my mistakes and switched to the mixed mode of AOF RDB, optimized the AOF logs, configured a suitable rewrite strategy, and never had similar problems again.

Next, let’s use some code to simulate these two persistence methods:

 <code class="python"># 模拟RDB快照def rdb_snapshot(data): import pickle with open("rdb.dump", "wb") as f: pickle.dump(data, f) print("RDB snapshot created.") # 模拟AOF日志def aof_log(data, operation): with open("aof.log", "a") as f: f.write(f"{operation}:{data}\n") print(f"AOF log entry added: {operation}:{data}") # 示例数据data = {"key1": "value1", "key2": "value2"} # 创建RDB快照rdb_snapshot(data) # 模拟一些写操作并记录AOF日志aof_log(data, "SET") data["key3"] = "value3" aof_log(data, "SET") # 模拟Redis重启，从RDB或AOF恢复数据(这里只做模拟，实际恢复需要更复杂的逻辑) # ... (恢复数据代码) ...</code>

This is just a simple simulation, and the actual Redis persistence mechanism is much more complicated than this. To play with Redis persistence, you need to have a deep understanding of operating system IO, file system, and even some underlying details. Remember, if there is no silver bullet, choosing the right persistence solution and performing reasonable configuration and monitoring is the king. Don’t expect a simple configuration to solve all problems. Only by making real knowledge through practice, do more hands-on, and hitting more pitfalls can you become a true Redis master.

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