Heroku Redis Metrics Logs

Last updated 25 January 2021

Customers using Heroku Redis premium instances will see Redis-related events on their app’s log stream. This can be useful for recording and analyzing usage over time.

Heroku Redis metrics which appear via heroku-redis are separate from standard alerts emitted from Redis itself which appear for all applications via redis.

Log format

2015-09-10T20:52:43+00:00 app[heroku-redis]: source=REDIS addon=redis-metric-98068 sample#active-connections=404 sample#load-avg-1m=0.115 sample#load-avg-5m=0.075 sample#load-avg-15m=0.07 sample#read-iops=0 sample#write-iops=54.758 sample#memory-total=15405660kB sample#memory-free=12639520kB sample#memory-cached=1911724kB sample#memory-redis=343477584bytes sample#hit-rate=0.7 sample#evicted-keys=0

The following attributes appear in application logs for all premium plans:

  • source: The instance attachment name that the measurements relate to.
  • addon: The instance addon name that the measurements relate to.
  • The log line’s timestamp is the time at which the measurements were taken.

Redis instance metrics

These attributes apply to a particular Redis instance:

  • sample#active-connections: The number of connections established on the Redis instance.
  • sample#memory-redis: Approximate amount of memory used by your Redis instance processes in bytes.
  • sample#hit-rate: The ratio of successful reads out of all read operations, rounded to five decimal points.
  • sample#evicted_keys: The number of evicted keys due to reaching your instance maxmemory limit.

Server metrics

For multi-tenant plans, server metrics include other Redis instances running on the shared server, and may be misleading when diagnosing Redis performance.

Server metrics come directly from the server operating system:

  • sample#load-avg-1m, sample#load-avg-5m and sample#load-avg-15m: The average system load over a period of 1 minute, 5 minutes and 15 minutes, divided by the number of available CPUs. A load-avg of 1.0 indicates that, on average, processes were requesting CPU resources for 100% of the timespan. This number includes I/O wait.
  • sample#read-iops and sample#write-iops: Number of read or write operations in I/O sizes of 16KB blocks.
  • sample#memory-total: Total amount of server memory in use, in kB. This includes memory used by all Redis processes, OS memory, and disk cache.
  • sample#memory-free: Amount of free memory available in kB.
  • sample#memory-cached: Amount of memory being used the OS for page cache, in kB.

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