How to calculate redis memory used percentage on ElastiCache

Question

I want to monitor my redis cache cluster on ElastiCache. From AWS/Elasticache i am able to get metrics like FreeableMemory and BytesUsedForCache. If i am not wrong BytesUsedForCache is the memory used by cluster(assuming there is only one node in cluster). I want to calculate percentage uses of memory. Can any one help me to get percentage of Memory uses in Redis.

Answer 1

By comparing the freeableMemory and bytesUsedForCache metrics, you will have the available memory for the Elasticache non-cluster mode (not sure if it applies to cluster-mode too).

Here is the NRQL we're using to monitor the cache:

SELECT Max(`provider.bytesUsedForCache.Sum`) / (Max(`provider.bytesUsedForCache.Sum`) + Min(`provider.freeableMemory.Sum`)) * 100 FROM DatastoreSample WHERE provider = 'ElastiCacheRedisNode'

This is based on the following:

• FreeableMemory: The amount of free memory available on the host. This is derived from the RAM, buffers and cache that the OS reports as freeable.AWS CacheMetrics HostLevel
• BytesUsedForCache: The total number of bytes allocated by Redis for all purposes, including the dataset, buffers, etc. This is derived from used_memory statistic at Redis INFO.AWS CacheMetrics Redis

So BytesUsedForCache (amount of memory used by Redis) + FreeableMemory (amount of data that Redis can have access to) = total memory that Redis can use.