| 1 | ### Understand the alert |
| 2 | |
| 3 | This alert, `memcached_cache_fill_rate`, measures the average rate at which the Memcached cache fills up (positive value) or frees up (negative value) space over the last hour. The units are in `KB/hour`. If you receive this alert, it means that your Memcached cache is either filling up or freeing up space at a noticeable rate. |
| 4 | |
| 5 | ### What is Memcached? |
| 6 | |
| 7 | Memcached is a high-performance, distributed memory object caching system used to speed up web applications by temporarily storing frequently-used data in RAM. It reduces the load on the database and improves performance by minimizing the need for repeated costly database queries. |
| 8 | |
| 9 | ### Troubleshoot the alert |
| 10 | |
| 11 | 1. Check the current cache usage: |
| 12 | |
| 13 | You can view the current cache usage using the following command, where `IP` and `PORT` are the Memcached server's IP address and port number: |
| 14 | |
| 15 | ``` |
| 16 | echo "stats" | nc IP PORT |
| 17 | ``` |
| 18 | |
| 19 | Look for the `bytes` and `limit_maxbytes` fields in the output to see the current cache usage and the maximum cache size allowed, respectively. |
| 20 | |
| 21 | 2. Identify heavy cache users: |
| 22 | |
| 23 | Find out which applications or services are generating a significant number of requests to Memcached. You may be able to optimize them to reduce cache usage. You can check Memcached logs for more details about requests and operations. |
| 24 | |
| 25 | 3. Optimize cache storage: |
| 26 | |
| 27 | If the cache is filling up too quickly, consider optimizing your cache storage policies. For example, you can adjust the expiration times of stored items, prioritize essential data, or use a more efficient caching strategy. |
| 28 | |
| 29 | 4. Increase the cache size: |
| 30 | |
| 31 | If needed, you can increase the cache size to accommodate a higher fill rate. To do this, stop the Memcached service and restart it with the `-m` option, specifying the desired memory size in megabytes: |
| 32 | |
| 33 | ``` |
| 34 | memcached -d -u memcached -m NEW_SIZE -l IP -p PORT |
| 35 | ``` |
| 36 | |
| 37 | Replace `NEW_SIZE` with the desired cache size in MB. |
| 38 | |
| 39 | ### Useful resources |
| 40 | |
| 41 | 1. [Memcached Official Site](https://memcached.org/) |