Use seconds where possible, and convert to milliseconds for Influxdb consumption

changelogs/unreleased/pawel-reduce_cardinality_of_prometheus_metrics.yml

+---
+title: Reduce the number of buckets in gitlab_cache_operation_duration_seconds
+merge_request: 15881
+author:
+type: changed

lib/gitlab/metrics/method_call.rb

@@ -4,7 +4,7 @@ module Gitlab
     class MethodCall
       MUTEX = Mutex.new
       BASE_LABELS = { module: nil, method: nil }.freeze
-      attr_reader :real_time_seconds, :cpu_time, :call_count, :labels
+      attr_reader :real_time, :cpu_time, :call_count, :labels
 
       def self.call_duration_histogram
         return @call_duration_histogram if @call_duration_histogram
@@ -27,42 +27,38 @@ module Gitlab
         @transaction = transaction
         @name = name
         @labels = { module: @module_name, method: @method_name }
-        @real_time_seconds = 0.0
-        @cpu_time = 0
+        @real_time = 0.0
+        @cpu_time = 0.0
         @call_count = 0
       end
 
       # Measures the real and CPU execution time of the supplied block.
       def measure
-        start_real_seconds = System.monotonic_time
+        start_real = System.monotonic_time
         start_cpu = System.cpu_time
         retval = yield
 
-        real_time_seconds = System.monotonic_time - start_real_seconds
+        real_time = System.monotonic_time - start_real
         cpu_time = System.cpu_time - start_cpu
 
-        @real_time_seconds += real_time_seconds
+        @real_time += real_time
         @cpu_time += cpu_time
         @call_count += 1
 
         if call_measurement_enabled? && above_threshold?
-          self.class.call_duration_histogram.observe(@transaction.labels.merge(labels), real_time_seconds)
+          self.class.call_duration_histogram.observe(@transaction.labels.merge(labels), real_time)
         end
 
         retval
       end
 
-      def real_time_milliseconds
-        real_time_seconds.in_milliseconds.to_i
-      end
-
       # Returns a Metric instance of the current method call.
       def to_metric
         Metric.new(
           Instrumentation.series,
           {
-            duration: real_time_milliseconds,
-            cpu_duration: cpu_time,
+            duration: real_time.in_milliseconds.to_i,
+            cpu_duration: cpu_time.in_milliseconds.to_i,
             call_count: call_count
           },
           method: @name
@@ -72,7 +68,7 @@ module Gitlab
       # Returns true if the total runtime of this method exceeds the method call
       # threshold.
       def above_threshold?
-        real_time_milliseconds >= Metrics.method_call_threshold
+        real_time.in_milliseconds >= Metrics.method_call_threshold
       end
 
       def call_measurement_enabled?

lib/gitlab/metrics/system.rb

@@ -35,19 +35,19 @@ module Gitlab
       if Process.const_defined?(:CLOCK_THREAD_CPUTIME_ID)
         def self.cpu_time
           Process
-            .clock_gettime(Process::CLOCK_THREAD_CPUTIME_ID, :millisecond)
+            .clock_gettime(Process::CLOCK_THREAD_CPUTIME_ID, :float_second)
         end
       else
         def self.cpu_time
           Process
-            .clock_gettime(Process::CLOCK_PROCESS_CPUTIME_ID, :millisecond)
+            .clock_gettime(Process::CLOCK_PROCESS_CPUTIME_ID, :float_second)
         end
       end
 
       # Returns the current real time in a given precision.
       #
-      # Returns the time as a Fixnum.
-      def self.real_time(precision = :millisecond)
+      # Returns the time as a Float for precision = :float_second.
+      def self.real_time(precision = :float_second)
         Process.clock_gettime(Process::CLOCK_REALTIME, precision)
       end
 

spec/lib/gitlab/metrics/method_call_spec.rb

@@ -8,8 +8,7 @@ describe Gitlab::Metrics::MethodCall do
     it 'measures the performance of the supplied block' do
       method_call.measure { 'foo' }
 
-      expect(method_call.real_time_seconds).to be_a_kind_of(Numeric)
-      expect(method_call.real_time_milliseconds).to be_a_kind_of(Numeric)
+      expect(method_call.real_time).to be_a_kind_of(Numeric)
       expect(method_call.cpu_time).to be_a_kind_of(Numeric)
       expect(method_call.call_count).to eq(1)
     end
@@ -65,14 +64,17 @@ describe Gitlab::Metrics::MethodCall do
 
   describe '#to_metric' do
     it 'returns a Metric instance' do
+      expect(method_call).to receive(:real_time).and_return(4.0001)
+      expect(method_call).to receive(:cpu_time).and_return(3.0001)
+
       method_call.measure { 'foo' }
       metric = method_call.to_metric
 
       expect(metric).to be_an_instance_of(Gitlab::Metrics::Metric)
       expect(metric.series).to eq('rails_method_calls')
 
-      expect(metric.values[:duration]).to be_a_kind_of(Numeric)
-      expect(metric.values[:cpu_duration]).to be_a_kind_of(Numeric)
+      expect(metric.values[:duration]).to eq(4000)
+      expect(metric.values[:cpu_duration]).to eq(3000)
       expect(metric.values[:call_count]).to be_an(Integer)
 
       expect(metric.tags).to eq({ method: 'Foo#bar' })
@@ -85,13 +87,13 @@ describe Gitlab::Metrics::MethodCall do
     end
 
     it 'returns false when the total call time is not above the threshold' do
-      expect(method_call).to receive(:real_time_seconds).and_return(0.009)
+      expect(method_call).to receive(:real_time).and_return(0.009)
 
       expect(method_call.above_threshold?).to eq(false)
     end
 
     it 'returns true when the total call time is above the threshold' do
-      expect(method_call).to receive(:real_time_seconds).and_return(9)
+      expect(method_call).to receive(:real_time).and_return(9)
 
       expect(method_call.above_threshold?).to eq(true)
     end
@@ -132,7 +134,7 @@ describe Gitlab::Metrics::MethodCall do
   describe '#real_time' do
     context 'without timings' do
       it 'returns 0.0' do
-        expect(method_call.real_time_seconds).to eq(0.0)
+        expect(method_call.real_time).to eq(0.0)
       end
     end
 
@@ -140,7 +142,7 @@ describe Gitlab::Metrics::MethodCall do
       it 'returns the total real time' do
         method_call.measure { 'foo' }
 
-        expect(method_call.real_time_seconds >= 0.0).to be(true)
+        expect(method_call.real_time >= 0.0).to be(true)
       end
     end
   end

spec/lib/gitlab/metrics/system_spec.rb

@@ -29,13 +29,13 @@ describe Gitlab::Metrics::System do
 
   describe '.cpu_time' do
     it 'returns a Fixnum' do
-      expect(described_class.cpu_time).to be_an(Integer)
+      expect(described_class.cpu_time).to be_an(Float)
     end
   end
 
   describe '.real_time' do
     it 'returns a Fixnum' do
-      expect(described_class.real_time).to be_an(Integer)
+      expect(described_class.real_time).to be_an(Float)
     end
   end