Cache Metrics

Metrician can automatically report metrics about calls your application makes to the common caches redis and memcached if you are using the redis gem, or one of memcached gem or dalli gem, respectively. If you need metrics about the service itself, rather than your application's interaction with it, then check out instrumentald.

Configuration

Metrician accepts 2 configuration options for cache metric collection in metrician.yaml. Cache metrics are enabled by default. For each call to memcached or redis, Metrician can be configured to also report the command used (e.g. GET/SET for memcached, HGET/ZRANK/MGET for redis) as part of the metric. The following are the default settings.

:cache:
  :enabled: true
  :command:
    :enabled: true
  :command_specific:
    :enabled: false

Metrics

Metrician can report the following metrics. Only app.cache.command is recorded by default.
app.cache.command average query execution time (ms)
app.cache.command.<command_name> avg. query execution time (ms) by command

Cache Metrics Query Language Expressions

To get the raw count of commands your application is sending to your cache service, add the following expression to a graph:

gauge_count(app.cache.command)

If you have enabled command_specific metrics and are using Memcached, determine your read-write ratio with this expression:

gauge_count(app.cache.command.get) / gauge_count(app.cache.command.set)
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