Cache hit ratio is a metric that measures the efficiency of key retrieval in a database.
Cache hit ratio is the ratio of key hits against the total number of key hits and misses.
The cache hit ratio plot tracks read efficiency, measured by the proportion of reads from cache versus the total reads from both disk and cache. With the exception of data warehouse use cases, an ideal cache hit ratio is 99% or higher, meaning that at least 99% of reads are from cache and no more than 1% are from disk.
If your cache hit ratio is consistently lower than 99%, consider upgrading to a plan with additional memory to increase your cache size.
For more information on monitoring PostgreSQL clusters, see How to Monitor PostgreSQL Database Performance.
The cache hit ratio plot displays the efficiency of key retrieval from the Redis cache. The Redis cache defines the ratio of key hits to the total number of key hits and misses. Key misses occur when a key has been expired or evicted from the cache, or it never existed.
For optimal responsiveness, keep your cache hit ratio at 0.8 or higher.
For more information on monitoring Redis clusters, see How to Monitor Redis Database Cluster Performance.