Troubleshooting | Administration

Introduction

Redis is an in-memory data structure store used as a database, cache, and message broker. Despite its robustness, you may encounter issues that require troubleshooting. This guide provides a comprehensive approach to troubleshooting Redis, from common problems to advanced diagnostics.

Common Issues

Some of the most common issues you might encounter with Redis include:

Connection problems
High memory usage
Slow performance
Data persistence issues

Connection Problems

Connection issues can arise due to network problems, incorrect configurations, or server overload.

Check Redis Server Status

First, ensure that the Redis server is running:

redis-cli ping

PONG

If you don't receive a PONG response, check if the Redis service is active:

sudo systemctl status redis

High Memory Usage

Redis stores data in memory, which can lead to high memory usage. Monitor the memory usage with the info command:

redis-cli info memory

The output will show memory-related metrics:

used_memory:1048576
used_memory_human:1M
used_memory_rss:2097152
used_memory_peak:2097152

If memory usage is too high, consider setting a max memory limit:

maxmemory 256mb

Slow Performance

Slow performance can be due to various reasons including high CPU usage, slow network, or large datasets. Use the slowlog command to identify slow queries:

redis-cli slowlog get

The output will list slow queries:

1) 1) (integer) 15
   2) (integer) 1496897112
   3) (integer) 12345
   4) 1) "SET"
      2) "key"
      3) "value"

Data Persistence Issues

Redis supports data persistence through RDB snapshots and AOF logs. Ensure that these are configured correctly.

Check RDB Snapshot

Verify the last RDB snapshot with:

redis-cli info persistence

Look for the rdb_last_save_time field:

rdb_last_save_time:1496897112

If the snapshot is not recent, manually trigger an RDB save:

redis-cli save

Advanced Diagnostics

For advanced diagnostics, use the following commands:

Monitor Command

Track real-time operations:

redis-cli monitor

Latency Command

Check for latency spikes:

redis-cli latency doctor

Conclusion

Troubleshooting Redis involves checking the server status, monitoring memory usage, identifying slow queries, and ensuring data persistence. By following these steps, you can diagnose and resolve common issues effectively.

Redis Troubleshooting