Troubleshooting Memcached: Common Issues
1. Memcached Not Starting
This is a common issue where Memcached fails to start due to various reasons, including configuration errors or port clashes.
To troubleshoot this, check the following:
- Ensure that the configuration file is correctly set up.
- Check if the port is already in use by another service.
Example Command:
If this command fails, review the logs for error messages.
2. Connection Refused Errors
These errors occur when clients try to connect to Memcached but cannot establish a connection. This can happen if Memcached is not running or if there are firewall rules blocking access.
To resolve this, try the following:
- Check if Memcached is running using
ps aux | grep memcached. - Inspect firewall settings to ensure that the Memcached port (default 11211) is open.
Example Output:
3. Memory Limit Reached
If Memcached reaches its memory limit, it will start evicting items to make room for new data, which can lead to performance issues or cache misses.
To check the current memory usage, use:
Adjust the memory limit by modifying the configuration file and restarting Memcached.
Example Configuration:
This sets the memory limit to 512 MB.
4. Data Not Being Cached
If your application is not caching data as expected, there could be several reasons such as incorrect set commands or issues in your application logic.
Ensure that you are using the correct commands to store data:
Example Command:
This command sets the key my_key with a time-to-live of 3600 seconds. Check for any errors in your application code that might prevent data from being stored.
5. Slow Performance
If Memcached is running slowly, it could be due to high load, inadequate memory allocation, or network issues. Monitor performance using:
Look for metrics such as cmd_get, cmd_set, and evictions. If evictions are high, consider increasing memory allocation.
Example Output:
This indicates that 100 items have been evicted from the cache. Increasing memory can help reduce this.