1 files changed, 58 insertions, 0 deletions
diff --git a/lib/gitlab/metrics/samplers/database_sampler.rb b/lib/gitlab/metrics/samplers/database_sampler.rb
new file mode 100644
index 00000000000..9ee4b0960c5
--- /dev/null
+++ b/lib/gitlab/metrics/samplers/database_sampler.rb
@@ -0,0 +1,58 @@
+# frozen_string_literal: true
+
+module Gitlab
+  module Metrics
+    module Samplers
+      class DatabaseSampler < BaseSampler
+        SAMPLING_INTERVAL_SECONDS = 5
+
+        METRIC_PREFIX = 'gitlab_database_connection_pool_'
+
+        METRIC_DESCRIPTIONS = {
+          size: 'Total connection pool capacity',
+          connections: 'Current connections in the pool',
+          busy: 'Connections in use where the owner is still alive',
+          dead: 'Connections in use where the owner is not alive',
+          idle: 'Connections not in use',
+          waiting: 'Threads currently waiting on this queue'
+        }.freeze
+
+        def metrics
+          @metrics ||= init_metrics
+        end
+
+        def sample
+          host_stats.each do |host_stat|
+            METRIC_DESCRIPTIONS.each_key do |metric|
+              metrics[metric].set(host_stat[:labels], host_stat[:stats][metric])
+            end
+          end
+        end
+
+        private
+
+        def init_metrics
+          METRIC_DESCRIPTIONS.map do |name, description|
+            [name, ::Gitlab::Metrics.gauge(:"#{METRIC_PREFIX}#{name}", description)]
+          end.to_h
+        end
+
+        def host_stats
+          return [] unless ActiveRecord::Base.connected?
+
+          [{ labels: labels_for_class(ActiveRecord::Base), stats: ActiveRecord::Base.connection_pool.stat }]
+        end
+
+        def labels_for_class(klass)
+          {
+            host: klass.connection_config[:host],
+            port: klass.connection_config[:port],
+            class: klass.to_s
+          }
+        end
+      end
+    end
+  end
+end
+
+Gitlab::Metrics::Samplers::DatabaseSampler.prepend_if_ee('EE::Gitlab::Metrics::Samplers::DatabaseSampler')