Collecting and Analyzing Redis Performance Metrics

Redis is an open source, in memory advance key value store with optional persistence to disk. Two common use of Redis is caching and publish-subscribe queues. 

How to access Redis performance metrics

Redis performance metrics is accessible through Redis command line interface (Redis-cli). Use the info command to print all performance metrics for your redis server.

Output of info command is grouped in following 10 groups :

1. server
2. client
3. memory
4. persistence
5. stats
6. replication
7. cpu
8. commandstats
9. cluster
10. keyspace

In case you just want to see metrics for any specific section, use info command. For example to print memory statistics for redis server use info memory :

Top Redis Performance Metrics:

• Memory Usage : used_memory

The used_memory metrics reports the total number of bytes allocated by Redis. This metrics reflects the amount of memory in bytes that Redis has requested to store your data and supporting metadata it needs to run. This metrics doesn't consider memory wastage due to fragmentation , meaning amount of memory reported by this parameter will always be different than total amount of memory that Redis has been allocated by Operating System.

• total_commands_processed

total_commands_processed metric give number of commands processed by Redis server. Tracking number of commands processed is critical for diagnosing latency issue in Redis instance. Because Redis is single threaded so commands are processed sequentially. The typical latency in 1 GB/s network is about 200 micro second. In case you are seeing slow response of commands and latency is greater than 200 micro second, this could be because of high number of commands in command queue.

• mem_fragmentation_ratio

The mem_fragmentation _ratio metrics gives the ratio of memory used as seen by the operating system (used_memory_rss) to memory allocated by Redis (used_memory)

Memory Fragmentation ratio = used_memory_rss/used_memory

If fragmentation ratio is outside range of 1 to 1.5 , it is likely sign of poor memory fragmentation by either Operating system or Redis instance.

• Evictions

The evicted_keys metrics gives number of keys removed by Redis due to hitting maxmemory limit.