Reduce the number of buckets for ElasticSearch

These are buckets of the time spent in ElasticSearch within a
transaction.

lib/gitlab/metrics/elasticsearch_rack_middleware.rb

@@ -4,7 +4,7 @@ module Gitlab
   module Metrics
     # Rack middleware for tracking Elasticsearch metrics from Grape and Web requests.
     class ElasticsearchRackMiddleware
-      HISTOGRAM_BUCKETS = [0.1, 0.25, 0.5, 1, 2.5, 5, 10, 60].freeze
+      HISTOGRAM_BUCKETS = [0.1, 0.5, 1, 10, 50].freeze
 
       def initialize(app)
         @app = app
@@ -28,6 +28,8 @@ module Gitlab
           docstring 'Amount of calls to Elasticsearch servers during web requests'
         end
 
+        return unless request_count > 0
+
         transaction.observe(:http_elasticsearch_requests_duration_seconds, query_time) do
           docstring 'Query time for Elasticsearch servers during web requests'
           buckets HISTOGRAM_BUCKETS

spec/lib/gitlab/metrics/elasticsearch_rack_middleware_spec.rb

@@ -38,5 +38,15 @@ RSpec.describe Gitlab::Metrics::ElasticsearchRackMiddleware do
 
       expect { middleware.call(env) }.to raise_error(StandardError)
     end
+
+    context 'when there are no elasticsearch requests' do
+      let(:elasticsearch_requests_count) { 0 }
+
+      it 'does not record duration if there were no ES calls' do
+        expect(transaction).not_to receive(:observe).with(:http_elasticsearch_requests_duration_seconds)
+
+        middleware.call(env)
+      end
+    end
   end
 end