John Davidson

Message:

As attached, Blackfire is reporting that all Redis actions have ridiculous latency with the Redis hosted on the same container. The hypervisor is not reporting high IO wait. The redis does not contain many keys but it is frequently accessed. How can this be happening? I've checked ulimit and the daemon files and increased the TCP port range. Just clueless what this is.

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My Answer:
There could be several reasons for the high IO wait reported for PHP accessing Redis. Here are a few things you can check and try to improve the performance:

1. Check the Redis configuration: Make sure that the Redis configuration is optimized for performance. You can check the maxclients setting in the Redis configuration file and increase it if necessary. Also, check the maxmemory setting to ensure that Redis has enough memory allocated for its operations.

2. Check the network latency: If the Redis server is hosted on a different container or server, there could be network latency causing the high IO wait. You can try to optimize the network settings or consider hosting Redis on the same container as PHP to reduce latency.

3. Check for any bottlenecks: Use tools like top, iostat, or vmstat to monitor the system resources and identify any bottlenecks that could be causing the high IO wait. Look for any processes consuming a lot of CPU or memory, as well as any disk or network bottlenecks.

4. Optimize PHP code: Make sure that the PHP code accessing Redis is optimized and efficient. Avoid making unnecessary or frequent Redis calls, and consider using caching to reduce the number of Redis requests.

5. Consider using a Redis cluster: If the Redis server is under heavy load, consider setting up a Redis cluster to distribute the load and improve performance. This can help reduce the IO wait and improve overall performance.

By checking these factors and optimizing your setup, you should be able to reduce the high IO wait reported for PHP accessing Redis. If the issue persists, you may need to further investigate and troubleshoot to identify the root cause of the problem.