Instrument Caches

A cache can be used to speed up data retrieval, thereby improving application performance. Because instead of getting data from a potentially slow data layer, your application will be getting data from memory (in a best case scenario). Caching can speed up read-heavy workloads for applications like Q&A portals, gaming, media sharing, and social networking.

Sentry offers a cache-monitoring dashboard for getting an overview of your application's caches.

To make it possible for Sentry to give you an overview of your cache performance, you'll need to create two spans - one indicating that something is being put into the cache, and a second one indicating that something is being fetched from the cache.

Make sure that there's a transaction running when you create the spans. If you're using a web framework like Rails those transactions will be created for you automatically. See Performance Monitoring for more information.

For detailed information about which data can be set, see the Cache Module Developer Specification.

Manual Instrumentation

Follow the steps below to make sure your Cache related spans end up in Sentry correctly.

Add Span When Putting Data Into the Cache

1. Set the cache value with whatever cache library you happen to be using.
2. Wrap the part of your application that uses the cached value with Sentry.with_child_span { |span| ... }
3. Set op to cache.put.
4. Set cache.item_size to an integer representing the size of the cached item.

(The steps described above are documented in the snippet.)

key = 'myCacheKey123'
value = 'The value I want to cache.'

Sentry.with_child_span(op: 'cache.put') do |span|
  # Set a key in your cache using your custom caching solution
  my_cache.set(key, value)

  # Describe the cache server you are accessing
  span.set_data('network.peer.address', 'cache.example.com/supercache')
  span.set_data('network.peer.port', 9000)

  # Add the key(s) you want to set
  span.set_data('cache.key', [key])

  # Add the size of the value you stored in the cache
  span.set_data('cache.item_size', value.size)  # Warning: if value is very big this could use lots of memory
end

Add Span When Retrieving Data From the Cache

1. Fetch the cached value from whatever cache library you happen to be using.
2. Wrap the part of your application that uses the cached value with Sentry.with_child_span { |span| ... }
3. Set op to cache.get.
4. Set cache.hit to a boolean value representing whether the value was successfully fetched from the cache or not.
5. Set cache.item_size to an integer representing the size of the cached item.

(The steps described above are documented in the snippet.)

key = 'myCacheKey123'
value = nil

Sentry.with_child_span(op: 'cache.get') do |span|
  # Get a key from your caching solution
  value = my_cache.get(key)

  # Describe the cache server you are accessing
  span.set_data('network.peer.address', 'cache.example.com/supercache')
  span.set_data('network.peer.port', 9000)

  # Add the key(s) you just retrieved from the cache
  span.set_data('cache.key', [key])

  if value
    # If you retrieved a value, the cache was hit
    span.set_data('cache.hit', True)

    # Optionally also add the size of the value you retrieved
    span.set_data('cache.item_size', value.size)
  else
    # If you could not retrieve a value, it was a miss
    span.set_data('cache.hit', False)
  end
end

You should now have the right spans in place. Head over to the Cache dashboard to see how your cache is performing.