Farting around

lib/prometheus/client/counter.rb

@@ -10,11 +10,11 @@ def type
         :counter
       end
 
-      def increment(by: 1, labels: {})
+      def increment(by: 1, labels: {}, exemplar: nil)
         raise ArgumentError, 'increment must be a non-negative number' if by < 0
 
         label_set = label_set_for(labels)
-        @store.increment(labels: label_set, by: by)
+        @store.increment(labels: label_set, by: by, exemplar: exemplar)
       end
     end
   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: nil)
             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: nil)
             if @values_aggregation_mode == DirectFileStore::MOST_RECENT
               raise InvalidStoreSettingsError,
                     "The :most_recent aggregation does not support the use of increment"\
@@ -118,13 +118,13 @@ def increment(labels:, by: 1)
             end
           end
 
-          def get(labels:)
+          def get(labels:, with_exemplars: false)
             in_process_sync do
               internal_store.read_value(store_key(labels))
             end
           end
 
-          def all_values
+          def all_values(with_exemplars: false)
             stores_data = Hash.new{ |hash, key| hash[key] = [] }
 
             # There's no need to call `synchronize` here. We're opening a second handle to

lib/prometheus/client/data_stores/single_threaded.rb

@@ -1,3 +1,7 @@
+require "prometheus/client/value_with_exemplars"
+require "prometheus/client/exemplar_collection"
+require "prometheus/client/exemplar"
+
 module Prometheus
   module Client
     module DataStores
@@ -25,27 +29,41 @@ 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] = Prometheus::Client::ValueWithExemplars.new }
           end
 
           def synchronize
             yield
           end
 
-          def set(labels:, val:)
-            @internal_store[labels] = val.to_f
+          def set(labels:, val:, exemplar: nil)
+            @internal_store[labels].set(value: val, exemplar: exemplar)
           end
 
-          def increment(labels:, by: 1)
-            @internal_store[labels] += by
+          def increment(labels:, by: 1, exemplar: nil)
+            @internal_store[labels].increment(by: by, exemplar: exemplar)
           end
 
-          def get(labels:)
-            @internal_store[labels]
+          def get(labels:, with_exemplars: false)
+            if with_exemplars
+              @internal_store[labels]
+            else
+              @internal_store[labels].value
+            end
           end
 
-          def all_values
-            @internal_store.dup
+          def all_values(with_exemplars: false)
+            if with_exemplars
+              @internal_store.dup
+            else
+              # this mess is just for backwards compatibility
+              output = Hash.new { |hash, key| hash[key] = 0.0 }
+              @internal_store.keys.each do |k|
+                output[k] = @internal_store[k].value
+              end
+
+              output
+            end
           end
         end
 

lib/prometheus/client/data_stores/synchronized.rb

@@ -1,3 +1,8 @@
+# no idea why this is reuired but giving up for now
+require 'prometheus/client/exemplar'
+require 'prometheus/client/exemplar_collection'
+require 'prometheus/client/value_with_exemplars'
+
 module Prometheus
   module Client
     module DataStores
@@ -24,34 +29,50 @@ 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] = Prometheus::Client::ValueWithExemplars.new }
             @lock = Monitor.new
           end
 
           def synchronize
             @lock.synchronize { yield }
           end
 
-          def set(labels:, val:)
+          def set(labels:, val:, exemplar: nil)
             synchronize do
-              @internal_store[labels] = val.to_f
+              @internal_store[labels].set(value: val, exemplar: exemplar)
             end
           end
 
-          def increment(labels:, by: 1)
+          def increment(labels:, by: 1, exemplar: nil)
             synchronize do
-              @internal_store[labels] += by
+              @internal_store[labels].increment(by: by, exemplar: exemplar)
             end
           end
 
-          def get(labels:)
+          def get(labels:, with_exemplars: false)
             synchronize do
-              @internal_store[labels]
+              if with_exemplars
+                @internal_store[labels]
+              else
+                @internal_store[labels].value
+              end
             end
           end
 
-          def all_values
-            synchronize { @internal_store.dup }
+          def all_values(with_exemplars: false)
+            synchronize do
+              if with_exemplars
+                @internal_store.dup
+              else
+                # this mess is just for backwards compatibility
+                output = Hash.new { |hash, key| hash[key] = 0.0 }
+                @internal_store.keys.each do |k|
+                  output[k] = @internal_store[k].value
+                end
+
+                output
+              end
+            end
           end
         end
 

lib/prometheus/client/exemplar.rb

@@ -0,0 +1,34 @@
+# encoding: UTF-8
+
+module Prometheus
+  module Client
+
+    # Store a snapshot of metric data including an extra set of kv pairs for a specific moment in
+    # time and specific moment of code execution.
+    #
+    # Value is expected to be set after the exemplar is initialized.  Exemplars without a value will
+    # not be exported.
+    class Exemplar
+      # The kv pairs that make up the unique information in the exemplar.
+      #
+      # We generally store trace ids here
+      attr_reader :labels
+
+      # The time the exemplar was recorded
+      attr_reader :timestamp
+
+      # The value of the metric at the time the exemplar was recorded
+      attr_writer :value
+      attr_reader :value
+
+      def initialize(labels: {}, timestamp: nil)
+        @labels = labels
+        @timestamp = timestamp || Time.now.to_i
+      end
+
+      def empty?
+        value.nil?
+      end
+    end
+  end
+end

lib/prometheus/client/exemplar_collection.rb

@@ -0,0 +1,68 @@
+# encoding: UTF-8
+
+module Prometheus
+  module Client
+    class ExemplarCollection
+      include Enumerable
+
+      # store the exemplars attached to a metric + label set
+      def initialize
+        @collection = {}
+
+        # theoretical way to avoid causing a major memory leak
+        #
+        # This could store two minutes of requests with 2 requests per second with these settings.
+        # I am not clear on the situation where this wouldn't be enough but I am sure I will find it
+        @max_timestamps = 120
+        @max_exemplars = 240
+        @exemplar_count = 0
+      end
+
+      def add(exemplar)
+        cleanup_if_necessary
+        @collection[exemplar.timestamp] ||= []
+        @collection[exemplar.timestamp] << exemplar
+
+        exemplar
+      end
+
+      def most_recent
+        @collection[last_key]&.last
+      end
+
+      def last
+        most_recent
+      end
+
+      def each
+        @collection.keys.sort.each do |key|
+          @collection[key].each do |exemplar|
+            yield(exemplar)
+          end
+        end
+      end
+
+      def size
+        @exemplar_count
+      end
+
+      private
+
+      def cleanup_if_necessary
+        if @exemplar_count >= @max_exemplars || @collection.keys.size >= @max_timestamps
+          @exemplar_count -= @collection.delete(first_key)&.size
+        end
+
+        @exemplar_count += 1
+      end
+
+      def first_key
+        @collection.keys.sort&.first
+      end
+
+      def last_key
+        @collection.keys.sort&.last
+      end
+    end
+  end
+end