WIP

Gemfile

@@ -92,3 +92,11 @@ if RUBY_VERSION >= '2.4.0' && (RUBY_PLATFORM =~ /^x86_64-(darwin|linux)/)
   gem 'sorbet', '= 0.5.9672'
   gem 'spoom', '~> 1.1'
 end
+
+gem 'rails', '~> 6.1.0'
+gem 'pg', '>= 1.1', platform: :ruby
+gem 'activerecord-jdbcpostgresql-adapter', '>= 61', platform: :jruby
+gem 'sidekiq', '>= 6.1.2'
+gem 'sprockets', '< 4'
+gem 'lograge', '~> 0.11'
+gem 'i18n', '1.8.7', platform: :jruby # Removal pending: https://github.com/ruby-i18n/i18n/issues/555#issuecomment-772112169

lib/datadog/core/utils.rb

@@ -110,6 +110,36 @@ def self.extract_host_port(host_port)
 
         [match[1], match[2].to_i]
       end
+
+      # Remove the prefixed module names from `Class#name` or `Module#name`.
+      # @example
+      #  `App::Api::User` returns `User`.
+      # @param [String] class_name the result from a `Class#name` or `Module#name` call
+      # @return [String] the class or module name without its enclosing modules
+      def self.extract_class_name(class_name)
+        if idx = class_name.rindex("::")
+          class_name[(idx + 2)..-1]
+        else
+          class_name
+        end
+      end
+
+      # Converts CamelCase strings to snake_case.
+      # @example
+      #  `MyClass` returns `my_class`.
+      # @param [String] string a CamelCase string
+      # @return [String] the snake_case version of the provided string
+      def self.camel_to_snake_case(string)
+        first_letter = true
+        string.gsub(/[A-Z]/) { |upcase_char|
+          if first_letter # Don't add `_` at the beginning of the string.
+            first_letter = false
+            upcase_char.downcase
+          else
+            "_#{upcase_char.downcase}"
+          end
+        }
+      end
     end
   end
 end

lib/datadog/tracing/contrib/active_support/cache/instrumentation.rb

@@ -50,7 +50,7 @@ def start_trace_cache(payload)
               Datadog.logger.debug(e.message)
             end
 
-            def finish_trace_cache(payload)
+            def finish_trace_cache(payload, instance)
               return unless enabled?
 
               # retrieve the tracing context and continue the trace
@@ -59,11 +59,28 @@ def finish_trace_cache(payload)
               return unless span && !span.finished?
 
               begin
-                # discard parameters from the cache_store configuration
-                if defined?(::Rails)
-                  store, = *Array.wrap(::Rails.configuration.cache_store).flatten
-                  span.set_tag(Ext::TAG_CACHE_BACKEND, store)
-                end
+                # Rails-compatible storage adapter identification.
+                #
+                # This will return the same result as the symbol provided to `config.cache_store` in the
+                # Rails configuration block: https://github.com/rails/rails/blob/f2ab66da735f9382a923471e27aca12f07ec05cd/guides/source/caching_with_rails.md#configuration
+                #
+                # For example:
+                # `config.cache_store = :memory_store, { size: 64.megabytes }` will return `memory_store`.
+                #
+                # This makes the cache backend immediately identifiable by the user.
+                #
+                # A few downsides: it is a string-heavy process to convert the current adapter back into
+                # its Rails configuration name. Also, this process assumes all cache instances live under a flat
+                # namespace: if the user creates a custom cache adapter called `App::MemoryStore` it will clash
+                # with the built-in `memory_store` adapter when reported through the `rails.cache.backend` tag.
+                #
+                # DEV: This is implemented in its current form to ensure backwards compatibility:
+                # DEV: the previous iteration would to always return `Rails.configuration.cache_store`
+                # DEV: regardless of the storage backend being used, which is incorrect.
+                # DEV: This version supports any backend class that is currently being instrumented.
+                class_name = Utils.extract_class_name(instance.class.name)
+                store = Utils.camel_to_snake_case(class_name)
+                span.set_tag(Ext::TAG_CACHE_BACKEND, store)
 
                 normalized_key = ::ActiveSupport::Cache.expand_cache_key(payload.fetch(:key))
                 cache_key = Core::Utils.truncate(normalized_key, Ext::QUANTIZE_CACHE_MAX_KEY_SIZE)
@@ -128,7 +145,7 @@ def read(*args, &block)
                   raise e
                 end
               ensure
-                Instrumentation.finish_trace_cache(payload)
+                Instrumentation.finish_trace_cache(payload, self)
               end
             end
 
@@ -174,7 +191,7 @@ def fetch(*args, &block)
                   raise e
                 end
               ensure
-                Instrumentation.finish_trace_cache(payload)
+                Instrumentation.finish_trace_cache(payload, self)
               end
             end
 
@@ -222,7 +239,7 @@ def write(*args, &block)
                   raise e
                 end
               ensure
-                Instrumentation.finish_trace_cache(payload)
+                Instrumentation.finish_trace_cache(payload, self)
               end
             end
 
@@ -268,7 +285,7 @@ def delete(*args, &block)
                   raise e
                 end
               ensure
-                Instrumentation.finish_trace_cache(payload)
+                Instrumentation.finish_trace_cache(payload, self)
               end
             end
           end