Prometheus metrics first pass

metrics wip

2 files changed, 80 insertions, 0 deletions

diff --git a/lib/gitlab/metrics/dummy_metric.rb b/lib/gitlab/metrics/dummy_metric.rb
new file mode 100644
index 00000000000..d27bb83854a
--- /dev/null
+++ b/lib/gitlab/metrics/dummy_metric.rb
@@ -0,0 +1,29 @@
+module Gitlab
+  module Metrics
+    # Mocks ::Prometheus::Client::Metric and all derived metrics
+    class DummyMetric
+      def get(*args)
+        raise NotImplementedError
+      end
+
+      def values(*args)
+        raise NotImplementedError
+      end
+
+      # counter
+      def increment(*args)
+        # noop
+      end
+
+      # gauge
+      def set(*args)
+        # noop
+      end
+
+      # histogram / summary
+      def observe(*args)
+        # noop
+      end
+    end
+  end
+end
diff --git a/lib/gitlab/metrics/prometheus_sampler.rb b/lib/gitlab/metrics/prometheus_sampler.rb
new file mode 100644
index 00000000000..5f90d4f0b66
--- /dev/null
+++ b/lib/gitlab/metrics/prometheus_sampler.rb
@@ -0,0 +1,51 @@
+module Gitlab
+  module Metrics
+    # Class that sends certain metrics to InfluxDB at a specific interval.
+    #
+    # This class is used to gather statistics that can't be directly associated
+    # with a transaction such as system memory usage, garbage collection
+    # statistics, etc.
+    class PrometheusSamples
+      # interval - The sampling interval in seconds.
+      def initialize(interval = Metrics.settings[:sample_interval])
+        interval_half = interval.to_f / 2
+
+        @interval = interval
+        @interval_steps = (-interval_half..interval_half).step(0.1).to_a
+      end
+
+      def start
+        Thread.new do
+          Thread.current.abort_on_exception = true
+
+          loop do
+            sleep(sleep_interval)
+
+            sample
+          end
+        end
+      end
+
+      def sidekiq?
+        Sidekiq.server?
+      end
+
+      # Returns the sleep interval with a random adjustment.
+      #
+      # The random adjustment is put in place to ensure we:
+      #
+      # 1. Don't generate samples at the exact same interval every time (thus
+      #    potentially missing anything that happens in between samples).
+      # 2. Don't sample data at the same interval two times in a row.
+      def sleep_interval
+        while step = @interval_steps.sample
+          if step != @last_step
+            @last_step = step
+
+            return @interval + @last_step
+          end
+        end
+      end
+    end
+  end
+end