From 53dc9e83c34b2a0ee2651046de031566f5b925d2 Mon Sep 17 00:00:00 2001
From: Pawel Chojnacki <pawel@chojnacki.ws>
Date: Thu, 7 Dec 2017 19:49:44 +0100
Subject: [PATCH 01/10] Cache feature check for 5 minutes for MethodCall
 instrumentation toggle

---
 lib/gitlab/metrics/method_call.rb           |  4 +++-
 spec/lib/gitlab/metrics/method_call_spec.rb | 11 +++++++++++
 2 files changed, 14 insertions(+), 1 deletion(-)

diff --git a/lib/gitlab/metrics/method_call.rb b/lib/gitlab/metrics/method_call.rb
index 65d55576ac2..ab7e7a06a77 100644
--- a/lib/gitlab/metrics/method_call.rb
+++ b/lib/gitlab/metrics/method_call.rb
@@ -72,7 +72,9 @@ module Gitlab
       end
 
       def call_measurement_enabled?
-        Feature.get(:prometheus_metrics_method_instrumentation).enabled?
+        Rails.cache.fetch(:prometheus_metrics_method_instrumentation_enabled, expires_in: 5.minutes) do
+          Feature.get(:prometheus_metrics_method_instrumentation).enabled?
+        end
       end
     end
   end
diff --git a/spec/lib/gitlab/metrics/method_call_spec.rb b/spec/lib/gitlab/metrics/method_call_spec.rb
index 5341addf911..df4c5167497 100644
--- a/spec/lib/gitlab/metrics/method_call_spec.rb
+++ b/spec/lib/gitlab/metrics/method_call_spec.rb
@@ -23,6 +23,17 @@ describe Gitlab::Metrics::MethodCall do
           Feature.get(:prometheus_metrics_method_instrumentation).enable
         end
 
+        it 'feature check is cached for 5 minutes' do
+          allow(Feature.get(:prometheus_metrics_method_instrumentation)).to receive(:enabled?).and_call_original
+          allow(Rails.cache).to receive(:fetch).and_call_original
+
+          method_call.measure { 'foo' }
+          method_call.measure { 'foo' }
+
+          expect(Feature.get(:prometheus_metrics_method_instrumentation)).to have_received(:enabled?).twice
+          expect(Rails.cache).to have_received(:fetch).with(:prometheus_metrics_method_instrumentation_enabled, expires_in: 5.minutes).twice
+        end
+
         it 'observes the performance of the supplied block' do
           expect(described_class.call_duration_histogram)
             .to receive(:observe)

From b503e6ff423699f7556fb948051e9c180a7b89f0 Mon Sep 17 00:00:00 2001
From: Pawel Chojnacki <pawel@chojnacki.ws>
Date: Fri, 8 Dec 2017 19:36:30 +0100
Subject: [PATCH 02/10] Implement simple in memory cache that expires after 5
 minutes

---
 lib/gitlab/metrics/method_call.rb           | 26 +++++++++++++-----
 spec/lib/gitlab/metrics/method_call_spec.rb | 30 ++++++++++++++++-----
 2 files changed, 43 insertions(+), 13 deletions(-)

diff --git a/lib/gitlab/metrics/method_call.rb b/lib/gitlab/metrics/method_call.rb
index ab7e7a06a77..744c489d46e 100644
--- a/lib/gitlab/metrics/method_call.rb
+++ b/lib/gitlab/metrics/method_call.rb
@@ -18,6 +18,24 @@ module Gitlab
         end
       end
 
+      def self.call_measurement_enabled?
+        return @call_measurement_enabled unless call_measurement_enabled_cache_expired?
+        MUTEX.synchronize do
+          return @call_measurement_enabled unless call_measurement_enabled_cache_expired?
+          @call_measurement_enabled_cache_expires_at = Time.now + 5.minutes
+          @call_measurement_enabled = Feature.get(:prometheus_metrics_method_instrumentation).enabled?
+        end
+      end
+
+      def self.call_measurement_enabled_cache_expired?
+        @call_measurement_enabled.nil? || @call_measurement_enabled_cache_expires_at.nil? || @call_measurement_enabled_cache_expires_at < Time.now
+      end
+
+      def self.call_measurement_enabled_cache_expire
+        @call_measurement_enabled = nil
+        @call_measurement_enabled_cache_expires_at = nil
+      end
+
       # name - The full name of the method (including namespace) such as
       #        `User#sign_in`.
       #
@@ -45,7 +63,7 @@ module Gitlab
         @cpu_time += cpu_time
         @call_count += 1
 
-        if call_measurement_enabled? && above_threshold?
+        if self.class.call_measurement_enabled? && above_threshold?
           self.class.call_duration_histogram.observe(@transaction.labels.merge(labels), real_time / 1000.0)
         end
 
@@ -70,12 +88,6 @@ module Gitlab
       def above_threshold?
         real_time >= Metrics.method_call_threshold
       end
-
-      def call_measurement_enabled?
-        Rails.cache.fetch(:prometheus_metrics_method_instrumentation_enabled, expires_in: 5.minutes) do
-          Feature.get(:prometheus_metrics_method_instrumentation).enabled?
-        end
-      end
     end
   end
 end
diff --git a/spec/lib/gitlab/metrics/method_call_spec.rb b/spec/lib/gitlab/metrics/method_call_spec.rb
index df4c5167497..f514fdd70ed 100644
--- a/spec/lib/gitlab/metrics/method_call_spec.rb
+++ b/spec/lib/gitlab/metrics/method_call_spec.rb
@@ -20,18 +20,35 @@ describe Gitlab::Metrics::MethodCall do
 
       context 'prometheus instrumentation is enabled' do
         before do
+          allow(Feature.get(:prometheus_metrics_method_instrumentation)).to receive(:enabled?).and_call_original
+          described_class.call_measurement_enabled_cache_expire
           Feature.get(:prometheus_metrics_method_instrumentation).enable
         end
 
-        it 'feature check is cached for 5 minutes' do
-          allow(Feature.get(:prometheus_metrics_method_instrumentation)).to receive(:enabled?).and_call_original
-          allow(Rails.cache).to receive(:fetch).and_call_original
+        around do |example|
+          Timecop.freeze do
+            example.run
+          end
+        end
 
-          method_call.measure { 'foo' }
-          method_call.measure { 'foo' }
+        it 'caches subsequent invocations of feature check' do
+          10.times do
+            method_call.measure { 'foo' }
+          end
+
+          expect(Feature.get(:prometheus_metrics_method_instrumentation)).to have_received(:enabled?).once
+        end
+
+        it 'expires feature check cache after 5 minutes' do
+          10.times do
+            method_call.measure { 'foo' }
+          end
+
+          Timecop.travel(Time.now + 5.minutes) do
+            method_call.measure { 'foo' }
+          end
 
           expect(Feature.get(:prometheus_metrics_method_instrumentation)).to have_received(:enabled?).twice
-          expect(Rails.cache).to have_received(:fetch).with(:prometheus_metrics_method_instrumentation_enabled, expires_in: 5.minutes).twice
         end
 
         it 'observes the performance of the supplied block' do
@@ -45,6 +62,7 @@ describe Gitlab::Metrics::MethodCall do
 
       context 'prometheus instrumentation is disabled' do
         before do
+          described_class.call_measurement_enabled_cache_expire
           Feature.get(:prometheus_metrics_method_instrumentation).disable
         end
 

From 6af849644dd097f7b41a26ca8b49d274444db196 Mon Sep 17 00:00:00 2001
From: Pawel Chojnacki <pawel@chojnacki.ws>
Date: Fri, 8 Dec 2017 20:19:01 +0100
Subject: [PATCH 03/10] Set cache expire only once the cache is filled,  to
 avoid situation where old result is returned in parallel thread.

---
 lib/gitlab/metrics/method_call.rb | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/lib/gitlab/metrics/method_call.rb b/lib/gitlab/metrics/method_call.rb
index 744c489d46e..2f5c45966ff 100644
--- a/lib/gitlab/metrics/method_call.rb
+++ b/lib/gitlab/metrics/method_call.rb
@@ -20,10 +20,13 @@ module Gitlab
 
       def self.call_measurement_enabled?
         return @call_measurement_enabled unless call_measurement_enabled_cache_expired?
+
         MUTEX.synchronize do
           return @call_measurement_enabled unless call_measurement_enabled_cache_expired?
-          @call_measurement_enabled_cache_expires_at = Time.now + 5.minutes
+
           @call_measurement_enabled = Feature.get(:prometheus_metrics_method_instrumentation).enabled?
+          @call_measurement_enabled_cache_expires_at = Time.now + 5.minutes
+          @call_measurement_enabled
         end
       end
 

From 5904b033dba553636ae2a06cbf1469d8f19df040 Mon Sep 17 00:00:00 2001
From: Pawel Chojnacki <pawel@chojnacki.ws>
Date: Mon, 11 Dec 2017 22:24:07 +0100
Subject: [PATCH 04/10] Implemente measurement enabled cache using
 AtomicReference

---
 lib/gitlab/metrics/method_call.rb           | 31 +++++++++------------
 spec/lib/gitlab/metrics/method_call_spec.rb |  4 +--
 2 files changed, 15 insertions(+), 20 deletions(-)

diff --git a/lib/gitlab/metrics/method_call.rb b/lib/gitlab/metrics/method_call.rb
index 2f5c45966ff..dc56a10957d 100644
--- a/lib/gitlab/metrics/method_call.rb
+++ b/lib/gitlab/metrics/method_call.rb
@@ -2,6 +2,7 @@ module Gitlab
   module Metrics
     # Class for tracking timing information about method calls
     class MethodCall
+      MEASUREMENT_ENABLED_CACHE = Concurrent::AtomicReference.new({ enabled: false, expires_at: Time.now })
       MUTEX = Mutex.new
       BASE_LABELS = { module: nil, method: nil }.freeze
       attr_reader :real_time, :cpu_time, :call_count, :labels
@@ -18,25 +19,19 @@ module Gitlab
         end
       end
 
-      def self.call_measurement_enabled?
-        return @call_measurement_enabled unless call_measurement_enabled_cache_expired?
-
-        MUTEX.synchronize do
-          return @call_measurement_enabled unless call_measurement_enabled_cache_expired?
-
-          @call_measurement_enabled = Feature.get(:prometheus_metrics_method_instrumentation).enabled?
-          @call_measurement_enabled_cache_expires_at = Time.now + 5.minutes
-          @call_measurement_enabled
+      def call_measurement_enabled?
+        res = MEASUREMENT_ENABLED_CACHE.update do |cache|
+          if cache[:expires_at] < Time.now
+            {
+              enabled: Feature.get(:prometheus_metrics_method_instrumentation).enabled?,
+              expires_at: Time.now + 5.minutes
+            }
+          else
+            cache
+          end
         end
-      end
 
-      def self.call_measurement_enabled_cache_expired?
-        @call_measurement_enabled.nil? || @call_measurement_enabled_cache_expires_at.nil? || @call_measurement_enabled_cache_expires_at < Time.now
-      end
-
-      def self.call_measurement_enabled_cache_expire
-        @call_measurement_enabled = nil
-        @call_measurement_enabled_cache_expires_at = nil
+        res[:enabled]
       end
 
       # name - The full name of the method (including namespace) such as
@@ -66,7 +61,7 @@ module Gitlab
         @cpu_time += cpu_time
         @call_count += 1
 
-        if self.class.call_measurement_enabled? && above_threshold?
+        if call_measurement_enabled? && above_threshold?
           self.class.call_duration_histogram.observe(@transaction.labels.merge(labels), real_time / 1000.0)
         end
 
diff --git a/spec/lib/gitlab/metrics/method_call_spec.rb b/spec/lib/gitlab/metrics/method_call_spec.rb
index f514fdd70ed..eca6a2cb54a 100644
--- a/spec/lib/gitlab/metrics/method_call_spec.rb
+++ b/spec/lib/gitlab/metrics/method_call_spec.rb
@@ -21,7 +21,7 @@ describe Gitlab::Metrics::MethodCall do
       context 'prometheus instrumentation is enabled' do
         before do
           allow(Feature.get(:prometheus_metrics_method_instrumentation)).to receive(:enabled?).and_call_original
-          described_class.call_measurement_enabled_cache_expire
+          described_class::MEASUREMENT_ENABLED_CACHE.set({enabled: false, expires_at: Time.now - 1.second})
           Feature.get(:prometheus_metrics_method_instrumentation).enable
         end
 
@@ -62,7 +62,7 @@ describe Gitlab::Metrics::MethodCall do
 
       context 'prometheus instrumentation is disabled' do
         before do
-          described_class.call_measurement_enabled_cache_expire
+          described_class::MEASUREMENT_ENABLED_CACHE.set({enabled: false, expires_at: Time.now})
           Feature.get(:prometheus_metrics_method_instrumentation).disable
         end
 

From 408208bc2b75d28235092e9bb3821242fdad08fb Mon Sep 17 00:00:00 2001
From: Pawel Chojnacki <pawel@chojnacki.ws>
Date: Mon, 11 Dec 2017 23:39:40 +0100
Subject: [PATCH 05/10] Use AtomicFixNum to implement CAS isolated cache
 update.

i.e.
Using compare and swap we update the expires_at value.
The thread that actually is able to update this value will also set
the cache holding method_call enabled state
---
 lib/gitlab/metrics/method_call.rb           | 17 +++++++----------
 spec/lib/gitlab/metrics/method_call_spec.rb | 13 +++++++++----
 2 files changed, 16 insertions(+), 14 deletions(-)

diff --git a/lib/gitlab/metrics/method_call.rb b/lib/gitlab/metrics/method_call.rb
index dc56a10957d..2c1cb789314 100644
--- a/lib/gitlab/metrics/method_call.rb
+++ b/lib/gitlab/metrics/method_call.rb
@@ -2,7 +2,8 @@ module Gitlab
   module Metrics
     # Class for tracking timing information about method calls
     class MethodCall
-      MEASUREMENT_ENABLED_CACHE = Concurrent::AtomicReference.new({ enabled: false, expires_at: Time.now })
+      MEASUREMENT_ENABLED_CACHE = Concurrent::AtomicBoolean.new(false)
+      MEASUREMENT_ENABLED_CACHE_EXPIRES_AT = Concurrent::AtomicFixnum.new(Time.now.to_i)
       MUTEX = Mutex.new
       BASE_LABELS = { module: nil, method: nil }.freeze
       attr_reader :real_time, :cpu_time, :call_count, :labels
@@ -20,18 +21,14 @@ module Gitlab
       end
 
       def call_measurement_enabled?
-        res = MEASUREMENT_ENABLED_CACHE.update do |cache|
-          if cache[:expires_at] < Time.now
-            {
-              enabled: Feature.get(:prometheus_metrics_method_instrumentation).enabled?,
-              expires_at: Time.now + 5.minutes
-            }
-          else
-            cache
+        expires_at = MEASUREMENT_ENABLED_CACHE_EXPIRES_AT.value
+        if expires_at < Time.now.to_i
+          if MEASUREMENT_ENABLED_CACHE_EXPIRES_AT.compare_and_set(expires_at, (Time.now + 30.seconds).to_i)
+            MEASUREMENT_ENABLED_CACHE.value = Feature.get(:prometheus_metrics_method_instrumentation).enabled?
           end
         end
 
-        res[:enabled]
+        MEASUREMENT_ENABLED_CACHE.value
       end
 
       # name - The full name of the method (including namespace) such as
diff --git a/spec/lib/gitlab/metrics/method_call_spec.rb b/spec/lib/gitlab/metrics/method_call_spec.rb
index eca6a2cb54a..5ce62504245 100644
--- a/spec/lib/gitlab/metrics/method_call_spec.rb
+++ b/spec/lib/gitlab/metrics/method_call_spec.rb
@@ -21,7 +21,7 @@ describe Gitlab::Metrics::MethodCall do
       context 'prometheus instrumentation is enabled' do
         before do
           allow(Feature.get(:prometheus_metrics_method_instrumentation)).to receive(:enabled?).and_call_original
-          described_class::MEASUREMENT_ENABLED_CACHE.set({enabled: false, expires_at: Time.now - 1.second})
+          described_class::MEASUREMENT_ENABLED_CACHE_EXPIRES_AT.value = Time.now.to_i - 1
           Feature.get(:prometheus_metrics_method_instrumentation).enable
         end
 
@@ -39,12 +39,16 @@ describe Gitlab::Metrics::MethodCall do
           expect(Feature.get(:prometheus_metrics_method_instrumentation)).to have_received(:enabled?).once
         end
 
-        it 'expires feature check cache after 5 minutes' do
+        it 'expires feature check cache after 30 seconds' do
           10.times do
             method_call.measure { 'foo' }
           end
 
-          Timecop.travel(Time.now + 5.minutes) do
+          Timecop.travel(Time.now + 30.seconds) do
+            method_call.measure { 'foo' }
+          end
+
+          Timecop.travel(Time.now + 31.seconds) do
             method_call.measure { 'foo' }
           end
 
@@ -62,7 +66,8 @@ describe Gitlab::Metrics::MethodCall do
 
       context 'prometheus instrumentation is disabled' do
         before do
-          described_class::MEASUREMENT_ENABLED_CACHE.set({enabled: false, expires_at: Time.now})
+          described_class::MEASUREMENT_ENABLED_CACHE_EXPIRES_AT.value = Time.now.to_i - 1
+
           Feature.get(:prometheus_metrics_method_instrumentation).disable
         end
 

From ca176a9bfe2ce9555da16e134bb92779b85952ad Mon Sep 17 00:00:00 2001
From: Pawel Chojnacki <pawel@chojnacki.ws>
Date: Mon, 11 Dec 2017 23:52:28 +0100
Subject: [PATCH 06/10] move call_measurement_enabled? method to the bottom of
 the file

---
 lib/gitlab/metrics/method_call.rb | 22 +++++++++++-----------
 1 file changed, 11 insertions(+), 11 deletions(-)

diff --git a/lib/gitlab/metrics/method_call.rb b/lib/gitlab/metrics/method_call.rb
index 2c1cb789314..a6900225a27 100644
--- a/lib/gitlab/metrics/method_call.rb
+++ b/lib/gitlab/metrics/method_call.rb
@@ -20,17 +20,6 @@ module Gitlab
         end
       end
 
-      def call_measurement_enabled?
-        expires_at = MEASUREMENT_ENABLED_CACHE_EXPIRES_AT.value
-        if expires_at < Time.now.to_i
-          if MEASUREMENT_ENABLED_CACHE_EXPIRES_AT.compare_and_set(expires_at, (Time.now + 30.seconds).to_i)
-            MEASUREMENT_ENABLED_CACHE.value = Feature.get(:prometheus_metrics_method_instrumentation).enabled?
-          end
-        end
-
-        MEASUREMENT_ENABLED_CACHE.value
-      end
-
       # name - The full name of the method (including namespace) such as
       #        `User#sign_in`.
       #
@@ -83,6 +72,17 @@ module Gitlab
       def above_threshold?
         real_time >= Metrics.method_call_threshold
       end
+
+      def call_measurement_enabled?
+        expires_at = MEASUREMENT_ENABLED_CACHE_EXPIRES_AT.value
+        if expires_at < Time.now.to_i
+          if MEASUREMENT_ENABLED_CACHE_EXPIRES_AT.compare_and_set(expires_at, (Time.now + 30.seconds).to_i)
+            MEASUREMENT_ENABLED_CACHE.value = Feature.get(:prometheus_metrics_method_instrumentation).enabled?
+          end
+        end
+
+        MEASUREMENT_ENABLED_CACHE.value
+      end
     end
   end
 end

From fd0a5168542f3a69815c99dc21f39587064f872d Mon Sep 17 00:00:00 2001
From: Pawel Chojnacki <pawel@chojnacki.ws>
Date: Tue, 12 Dec 2017 00:23:56 +0100
Subject: [PATCH 07/10] use class variables instead of CONSTANTs

---
 lib/gitlab/metrics/method_call.rb           | 16 ++++++++++------
 spec/lib/gitlab/metrics/method_call_spec.rb |  4 ++--
 2 files changed, 12 insertions(+), 8 deletions(-)

diff --git a/lib/gitlab/metrics/method_call.rb b/lib/gitlab/metrics/method_call.rb
index a6900225a27..a844100e5a8 100644
--- a/lib/gitlab/metrics/method_call.rb
+++ b/lib/gitlab/metrics/method_call.rb
@@ -2,8 +2,8 @@ module Gitlab
   module Metrics
     # Class for tracking timing information about method calls
     class MethodCall
-      MEASUREMENT_ENABLED_CACHE = Concurrent::AtomicBoolean.new(false)
-      MEASUREMENT_ENABLED_CACHE_EXPIRES_AT = Concurrent::AtomicFixnum.new(Time.now.to_i)
+      @@measurement_enabled_cache = Concurrent::AtomicBoolean.new(false)
+      @@measurement_enabled_cache_expires_at = Concurrent::AtomicFixnum.new(Time.now.to_i)
       MUTEX = Mutex.new
       BASE_LABELS = { module: nil, method: nil }.freeze
       attr_reader :real_time, :cpu_time, :call_count, :labels
@@ -20,6 +20,10 @@ module Gitlab
         end
       end
 
+      def self.measurement_enabled_cache_expires_at
+        @@measurement_enabled_cache_expires_at
+      end
+
       # name - The full name of the method (including namespace) such as
       #        `User#sign_in`.
       #
@@ -74,14 +78,14 @@ module Gitlab
       end
 
       def call_measurement_enabled?
-        expires_at = MEASUREMENT_ENABLED_CACHE_EXPIRES_AT.value
+        expires_at = @@measurement_enabled_cache_expires_at.value
         if expires_at < Time.now.to_i
-          if MEASUREMENT_ENABLED_CACHE_EXPIRES_AT.compare_and_set(expires_at, (Time.now + 30.seconds).to_i)
-            MEASUREMENT_ENABLED_CACHE.value = Feature.get(:prometheus_metrics_method_instrumentation).enabled?
+          if @@measurement_enabled_cache_expires_at.compare_and_set(expires_at, (Time.now + 30.seconds).to_i)
+            @@measurement_enabled_cache.value = Feature.get(:prometheus_metrics_method_instrumentation).enabled?
           end
         end
 
-        MEASUREMENT_ENABLED_CACHE.value
+        @@measurement_enabled_cache.value
       end
     end
   end
diff --git a/spec/lib/gitlab/metrics/method_call_spec.rb b/spec/lib/gitlab/metrics/method_call_spec.rb
index 5ce62504245..f98d7e48b17 100644
--- a/spec/lib/gitlab/metrics/method_call_spec.rb
+++ b/spec/lib/gitlab/metrics/method_call_spec.rb
@@ -21,7 +21,7 @@ describe Gitlab::Metrics::MethodCall do
       context 'prometheus instrumentation is enabled' do
         before do
           allow(Feature.get(:prometheus_metrics_method_instrumentation)).to receive(:enabled?).and_call_original
-          described_class::MEASUREMENT_ENABLED_CACHE_EXPIRES_AT.value = Time.now.to_i - 1
+          described_class.measurement_enabled_cache_expires_at.value = Time.now.to_i - 1
           Feature.get(:prometheus_metrics_method_instrumentation).enable
         end
 
@@ -66,7 +66,7 @@ describe Gitlab::Metrics::MethodCall do
 
       context 'prometheus instrumentation is disabled' do
         before do
-          described_class::MEASUREMENT_ENABLED_CACHE_EXPIRES_AT.value = Time.now.to_i - 1
+          described_class.measurement_enabled_cache_expires_at.value = Time.now.to_i - 1
 
           Feature.get(:prometheus_metrics_method_instrumentation).disable
         end

From da19ce625ba8a0db9921fd85e331e70b14a5625b Mon Sep 17 00:00:00 2001
From: Pawel Chojnacki <pawel@chojnacki.ws>
Date: Tue, 12 Dec 2017 18:52:08 +0100
Subject: [PATCH 08/10] Expire feature flag cache after 1minute

---
 lib/gitlab/metrics/method_call.rb           |  2 +-
 spec/lib/gitlab/metrics/method_call_spec.rb | 10 ++++------
 2 files changed, 5 insertions(+), 7 deletions(-)

diff --git a/lib/gitlab/metrics/method_call.rb b/lib/gitlab/metrics/method_call.rb
index a844100e5a8..c58e54916e6 100644
--- a/lib/gitlab/metrics/method_call.rb
+++ b/lib/gitlab/metrics/method_call.rb
@@ -80,7 +80,7 @@ module Gitlab
       def call_measurement_enabled?
         expires_at = @@measurement_enabled_cache_expires_at.value
         if expires_at < Time.now.to_i
-          if @@measurement_enabled_cache_expires_at.compare_and_set(expires_at, (Time.now + 30.seconds).to_i)
+          if @@measurement_enabled_cache_expires_at.compare_and_set(expires_at, 1.minute.from_now.to_i)
             @@measurement_enabled_cache.value = Feature.get(:prometheus_metrics_method_instrumentation).enabled?
           end
         end
diff --git a/spec/lib/gitlab/metrics/method_call_spec.rb b/spec/lib/gitlab/metrics/method_call_spec.rb
index f98d7e48b17..c11da42ed29 100644
--- a/spec/lib/gitlab/metrics/method_call_spec.rb
+++ b/spec/lib/gitlab/metrics/method_call_spec.rb
@@ -40,15 +40,13 @@ describe Gitlab::Metrics::MethodCall do
         end
 
         it 'expires feature check cache after 30 seconds' do
-          10.times do
+          method_call.measure { 'foo' }
+
+          Timecop.travel(1.minute.from_now) do
             method_call.measure { 'foo' }
           end
 
-          Timecop.travel(Time.now + 30.seconds) do
-            method_call.measure { 'foo' }
-          end
-
-          Timecop.travel(Time.now + 31.seconds) do
+          Timecop.travel(1.minute.from_now + 1.second) do
             method_call.measure { 'foo' }
           end
 

From 51668d3e1faa448ceecf5457db552c89314c9dbe Mon Sep 17 00:00:00 2001
From: Pawel Chojnacki <pawel@chojnacki.ws>
Date: Tue, 12 Dec 2017 22:30:27 +0100
Subject: [PATCH 09/10] Use class variable and add rubocop exception

---
 lib/gitlab/metrics/method_call.rb | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/lib/gitlab/metrics/method_call.rb b/lib/gitlab/metrics/method_call.rb
index c58e54916e6..9112164f22e 100644
--- a/lib/gitlab/metrics/method_call.rb
+++ b/lib/gitlab/metrics/method_call.rb
@@ -1,3 +1,5 @@
+# rubocop:disable Style/ClassVars
+
 module Gitlab
   module Metrics
     # Class for tracking timing information about method calls

From db9e5bf75e8546649ddd65a5696ff4edb87ded20 Mon Sep 17 00:00:00 2001
From: Pawel Chojnacki <pawel@chojnacki.ws>
Date: Wed, 13 Dec 2017 18:43:08 +0100
Subject: [PATCH 10/10] fix test case description

---
 spec/lib/gitlab/metrics/method_call_spec.rb | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/spec/lib/gitlab/metrics/method_call_spec.rb b/spec/lib/gitlab/metrics/method_call_spec.rb
index c11da42ed29..78767d06462 100644
--- a/spec/lib/gitlab/metrics/method_call_spec.rb
+++ b/spec/lib/gitlab/metrics/method_call_spec.rb
@@ -39,7 +39,7 @@ describe Gitlab::Metrics::MethodCall do
           expect(Feature.get(:prometheus_metrics_method_instrumentation)).to have_received(:enabled?).once
         end
 
-        it 'expires feature check cache after 30 seconds' do
+        it 'expires feature check cache after 1 minute' do
           method_call.measure { 'foo' }
 
           Timecop.travel(1.minute.from_now) do