Exemplar sketch

lib/prometheus/client/data_stores/README.md

@@ -102,11 +102,11 @@ module Prometheus
           # Store a value for this metric and a set of labels
           # Internally, may add extra "labels" to disambiguate values between,
           # for example, different processes
-          def set(labels:, val:)
+          def set(labels:, val:, exemplar_labels: {})
             raise NotImplementedError
           end
 
-          def increment(labels:, by: 1)
+          def increment(labels:, by: 1, exemplar_labels: {})
             raise NotImplementedError
           end
 

lib/prometheus/client/data_stores/direct_file_store.rb

@@ -99,13 +99,13 @@ def synchronize
             end
           end
 
-          def set(labels:, val:)
+          def set(labels:, val:, exemplar_labels: {}) # no exemplar support, this change to make tests pass
             in_process_sync do
               internal_store.write_value(store_key(labels), val.to_f)
             end
           end
 
-          def increment(labels:, by: 1)
+          def increment(labels:, by: 1, exemplar_labels: {}) # no exemplar support, this change to make tests pass
             if @values_aggregation_mode == DirectFileStore::MOST_RECENT
               raise InvalidStoreSettingsError,
                     "The :most_recent aggregation does not support the use of increment"\
@@ -263,6 +263,19 @@ def all_values
             end
           end
 
+          # I completely punted on this.  Here is a sketch of a solution with no promises that this is a good idea
+          # 
+          # Instead of storing a single value, store the following four values for each labelset on the metric:
+          # - value: 8 byte float
+          # - exemplar label: 140 bytes (fixed width)
+          #   128 bytes of label data + some amount of buffer for control characters generated in store_key (& = etc)
+          # - exemplar value: 8 byte float
+          # - exemplar timestamp: 8 byte float (need to double check the spec)
+          #
+          # - update @positions and @used for this wider value in init_value ~164 bytes
+          # - add read_value_with_exemplar and write_value_with_exemplar
+          # - keep read_value and write_value exactly the same.  The only difference when they run is
+          #   the return value of @positions[key] will have a bigger offset than before.
           def read_value(key)
             if !@positions.has_key?(key)
               init_value(key)

lib/prometheus/client/data_stores/single_threaded.rb

@@ -32,11 +32,11 @@ def synchronize
             yield
           end
 
-          def set(labels:, val:)
+          def set(labels:, val:, exemplar_labels: {}) # no exemplar support for now, this change to make tests pass
             @internal_store[labels] = val.to_f
           end
 
-          def increment(labels:, by: 1)
+          def increment(labels:, by: 1, exemplar_labels: {}) # no exemplar support for now, this change to make tests pass
             @internal_store[labels] += by
           end
 

lib/prometheus/client/data_stores/synchronized.rb

@@ -1,3 +1,5 @@
+require 'prometheus/client/value_with_exemplar'
+
 module Prometheus
   module Client
     module DataStores
@@ -24,33 +26,62 @@ def validate_metric_settings(metric_settings:)
 
         class MetricStore
           def initialize
-            @internal_store = Hash.new { |hash, key| hash[key] = 0.0 }
+            @internal_store = Hash.new { |hash, key| hash[key] = ValueWithExemplar.new }
             @lock = Monitor.new
           end
 
           def synchronize
             @lock.synchronize { yield }
           end
 
-          def set(labels:, val:)
+          def set(labels:, val:, exemplar_labels: {})
             synchronize do
-              @internal_store[labels] = val.to_f
+              vwe = @internal_store[labels]
+              vwe.value = val
+              vwe.setup_exemplar(exemplar_labels)
+
+              vwe.value
             end
           end
 
-          def increment(labels:, by: 1)
+          def increment(labels:, by: 1, exemplar_labels: {})
             synchronize do
-              @internal_store[labels] += by
+              vwe = @internal_store[labels]
+              vwe.value = vwe.value + by
+              vwe.setup_exemplar(exemplar_labels)
+
+              vwe.value
             end
           end
 
+          # get and get_with_exemplars probably combined into a single method eventually
           def get(labels:)
             synchronize do
-              @internal_store[labels]
+              @internal_store[labels].value
             end
           end
 
+          def get_with_exemplars(labels:)
+            synchronize do
+              @internal_store[labels]
+            end
+          end
+
+          # all_values and all_values_with_exemplars probably combined into a single method
+          # eventually
           def all_values
+            synchronize do
+              # this code is bad and I feel bad about it
+              new_store = Hash.new { |hash, key| hash[key] = 0.0 }
+              @internal_store.keys.each do |k|
+                new_store[k] = @internal_store[k].value
+              end
+
+              new_store
+            end
+          end
+
+          def all_values_with_exemplars
             synchronize { @internal_store.dup }
           end
         end

lib/prometheus/client/formats/open_metrics.rb

@@ -0,0 +1,21 @@
+# encoding: UTF-8
+
+module Prometheus
+  module Client
+    module Formats
+      module OpenMetrics
+        # used by the middleware to determine if this format works for the request
+        MEDIA_TYPE   = 'application/openmetrics-text'.freeze
+        VERSION      = '1.0.0'.freeze
+        CONTENT_TYPE = "#{MEDIA_TYPE}; version=#{VERSION}; charset=utf-8".freeze
+        DELIMITER = "\n".freeze
+        EOF = "# EOF\n".freeze
+
+        # public interface to generate out the /metrics payload
+        def self.marshal(registry)
+          "hello world"
+        end
+      end
+    end
+  end
+end

lib/prometheus/client/gauge.rb

@@ -12,12 +12,12 @@ def type
       end
 
       # Sets the value for the given label set
-      def set(value, labels: {})
+      def set(value, labels: {}, exemplar_labels: {})
         unless value.is_a?(Numeric)
           raise ArgumentError, 'value must be a number'
         end
 
-        @store.set(labels: label_set_for(labels), val: value)
+        @store.set(labels: label_set_for(labels), val: value, exemplar_labels: exemplar_labels)
       end
 
       def set_to_current_time(labels: {})
@@ -26,16 +26,16 @@ def set_to_current_time(labels: {})
 
       # Increments Gauge value by 1 or adds the given value to the Gauge.
       # (The value can be negative, resulting in a decrease of the Gauge.)
-      def increment(by: 1, labels: {})
+      def increment(by: 1, labels: {}, exemplar_labels: {})
         label_set = label_set_for(labels)
-        @store.increment(labels: label_set, by: by)
+        @store.increment(labels: label_set, by: by, exemplar_labels: exemplar_labels)
       end
 
       # Decrements Gauge value by 1 or subtracts the given value from the Gauge.
       # (The value can be negative, resulting in a increase of the Gauge.)
-      def decrement(by: 1, labels: {})
+      def decrement(by: 1, labels: {}, exemplar_labels: {})
         label_set = label_set_for(labels)
-        @store.increment(labels: label_set, by: -by)
+        @store.increment(labels: label_set, by: -by, exemplar_labels: exemplar_labels)
       end
     end
   end

lib/prometheus/client/value_with_exemplar.rb

@@ -0,0 +1,52 @@
+# encoding: UTF-8
+
+module Prometheus
+  module Client
+    class ValueWithExemplar
+      attr_accessor :value, :exemplar_labels, :exemplar_value, :exemplar_timestamp
+
+      def self.from_json(json)
+        attributes = JSON.parse(json)
+        new(attributes) # this needs some more initialize args to actually work
+      end
+
+      def initialize(val: 0)
+        self.value = val
+      end
+
+      def value=(new_val)
+        @value = new_val.to_f
+      end
+
+      # to be cleaned up
+      def setup_exemplar(data)
+        if !data.empty? # don't store an exemplar on an empty values hash (might need to be converted to a nil check)
+          now = Time.now
+
+          if !exemplar_timestamp # no previous exemplar set
+            exemplar_labels = data
+            exemplar_value = value
+            exemplar_timestamp = now
+          elsif now > exemplar_timestamp # previous exemplar in the past
+            exemplar_labels = data
+            exemplar_value = value
+            exemplar_timestamp = now
+          end
+        end
+      end
+
+      def to_hash
+        {
+          value: value,
+          exemplar_labels: exemplar_labels,
+          exemplar_value: exemplar_value,
+          exemplar_timestamp: exemplar_timestamp
+        }
+      end
+
+      def to_json
+        to_hash.to_json
+      end
+    end
+  end
+end

lib/prometheus/middleware/exporter.rb

@@ -2,6 +2,7 @@
 
 require 'prometheus/client'
 require 'prometheus/client/formats/text'
+require 'prometheus/client/formats/open_metrics'
 
 module Prometheus
   module Middleware
@@ -14,7 +15,7 @@ module Middleware
     class Exporter
       attr_reader :app, :registry, :path
 
-      FORMATS  = [Client::Formats::Text].freeze
+      FORMATS  = [Client::Formats::Text, Client::Formats::OpenMetrics].freeze # I think this is all that is needed but I might be missing something
       FALLBACK = Client::Formats::Text
 
       def initialize(app, options = {})

spec/prometheus/middleware/exporter_spec.rb

@@ -42,7 +42,7 @@
 
     shared_examples 'not acceptable' do |headers|
       it 'responds with 406 Not Acceptable' do
-        message = 'Supported media types: text/plain'
+        message = 'Supported media types: text/plain, application/openmetrics-text'
 
         get '/metrics', nil, headers