Store request methods/URIs as values

Since filtering by these values is very rare (they're mostly just
displayed as-is) we don't need to waste any index space by saving them
as tags. By storing them as values we also greatly reduce the number of
series in InfluxDB.

lib/gitlab/metrics/rack_middleware.rb

@@ -32,8 +32,8 @@ module Gitlab
       def transaction_from_env(env)
         trans = Transaction.new
 
-        trans.add_tag(:request_method, env['REQUEST_METHOD'])
+        trans.set(:request_uri, env['REQUEST_URI'])
-        trans.add_tag(:request_uri, env['REQUEST_URI'])
+        trans.set(:request_method, env['REQUEST_METHOD'])
 
         trans
       end

lib/gitlab/metrics/transaction.rb

@@ -4,7 +4,7 @@ module Gitlab
     class Transaction
       THREAD_KEY = :_gitlab_metrics_transaction
 
-      attr_reader :tags
+      attr_reader :tags, :values
 
       def self.current
         Thread.current[THREAD_KEY]
@@ -46,6 +46,10 @@ module Gitlab
         @values[name] += value
       end
 
+      def set(name, value)
+        @values[name] = value
+      end
+
       def add_tag(key, value)
         @tags[key] = value
       end

spec/lib/gitlab/metrics/rack_middleware_spec.rb

@@ -40,9 +40,9 @@ describe Gitlab::Metrics::RackMiddleware do
       expect(transaction).to be_an_instance_of(Gitlab::Metrics::Transaction)
     end
 
-    it 'tags the transaction with the request method and URI' do
+    it 'stores the request method and URI in the transaction as values' do
-      expect(transaction.tags[:request_method]).to eq('GET')
+      expect(transaction.values[:request_method]).to eq('GET')
-      expect(transaction.tags[:request_uri]).to eq('/foo')
+      expect(transaction.values[:request_uri]).to eq('/foo')
     end
   end
 

spec/lib/gitlab/metrics/transaction_spec.rb

@@ -50,6 +50,17 @@ describe Gitlab::Metrics::Transaction do
     end
   end
 
+  describe '#set' do
+    it 'sets a value' do
+      transaction.set(:number, 10)
+
+      expect(transaction).to receive(:add_metric).
+        with('transactions', { duration: 0.0, number: 10 }, {})
+
+      transaction.track_self
+    end
+  end
+
   describe '#add_tag' do
     it 'adds a tag' do
       transaction.add_tag(:foo, 'bar')