How to monitor Redis memory usage?

How to monitor Redis memory usage? Use the INFO memory command to view overall memory usage. Use the MEMORY USAGE key command to view the memory footprint of a single key. Use monitoring tools (such as Grafana, Prometheus) for visual monitoring, focusing on memory usage peaks. Periodically execute the MEMORY STATS command to check memory fragmentation. Optimize Redis configuration and application code based on monitoring results, such as limiting maximum memory usage, optimizing cache policies, and reducing memory usage.

How to monitor Redis memory usage? This question is a good question, which is much more sophisticated than asking "What is Redis"! After all, no matter how awesome Redis is, it will be useless if the memory is exploded.

In this article, we don’t mess with those who are stupid, and we just add real information. After reading it, you can not only monitor Redis memory, but also understand why you need to monitor and how to optimize it after monitoring.

Let’s talk about the basics first. You have to know that Redis is a memory-based database, and memory is its lifeblood. If there is not enough memory, it will stop. Therefore, monitoring memory usage is as important as a doctor taking blood pressure to a patient.

Redis itself provides several useful commands to help you understand the memory situation:

 <code class="bash">INFO memory</code>

This command, like Redis's physical examination report, will tell you various memory metrics, such as used_memory, used_memory_rss, etc. used_memory is the memory that Redis thinks is used, while used_memory_rss is the memory occupied by Redis seen by the operating system. These two values ​​usually have differences. This is related to the memory allocation mechanism of the operating system. Don't worry too much.

More advanced, you can use:

 <code class="bash">MEMORY USAGE key</code>

This command allows you to accurately measure how much memory a key occupies. This is very useful for finding out the memory "big users". Just imagine, you find that a key occupies a huge amount of memory, and it may be an outdated cache. At this time, you can delete it and release valuable memory resources.

But relying solely on command line monitoring is not real-time enough and not convenient enough. In production environment, you have to use monitoring tools, such as Grafana, Prometheus and Redis exporter. These tools can visualize Redis's memory information, allowing you to see the memory usage trend at a glance and discover exceptions in a timely manner.

Here is a tip: don't just stare at used_memory , but also used_memory_peak , which is the memory usage peak. If used_memory is always lower than used_memory_peak , it means that your memory is being used reasonably. If the two are similar, or even used_memory is close to used_memory_rss , then be careful, the memory may be about to explode.

Let’s talk about the pitfalls. Many students only focus on the total amount of memory and ignore memory fragmentation. With too much memory fragmentation, even if there is still a lot of free memory, it may not be allocated to the new key, causing Redis performance to decline or even crash. Therefore, it is also very important to execute the MEMORY STATS command regularly to check the memory fragmentation situation.

Finally, let’s talk about optimization. Monitoring is just the first step, and more importantly, it is to optimize Redis configuration and application code based on monitoring results. For example, you can adjust the configuration of Redis to limit the maximum memory usage; or optimize your cache strategy to reduce unnecessary cache data; or use smaller data types to reduce memory usage. These all need to be analyzed in detail based on actual conditions and specific issues. Remember, monitoring is just a means, and optimization is the goal. It's like a doctor prescribes medicine for you, and you have to take medicine on time to cure the disease.

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