Understand the alert
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.
What is Memcached?
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.
Troubleshoot the alert
- Check the current cache usage:
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:
echo "stats" | nc IP PORT
Look for the bytes and limit_maxbytes fields in the output to see the current cache usage and the maximum cache size allowed, respectively.
- Identify heavy cache users:
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.
- Optimize cache storage:
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.
- Increase the cache size:
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:
memcached -d -u memcached -m NEW_SIZE -l IP -p PORT
Replace NEW_SIZE with the desired cache size in MB.