1 files changed, 38 insertions, 0 deletions
diff --git a/lib/gitlab/database/migrations/observers/query_statistics.rb b/lib/gitlab/database/migrations/observers/query_statistics.rb
new file mode 100644
index 00000000000..466f4724256
--- /dev/null
+++ b/lib/gitlab/database/migrations/observers/query_statistics.rb
@@ -0,0 +1,38 @@
+# frozen_string_literal: true
+
+module Gitlab
+  module Database
+    module Migrations
+      module Observers
+        # This observer gathers statistics from the pg_stat_statements extension.
+        # Notice that this extension is not installed by default. In case it cannot
+        # be found, the observer does nothing and doesn't throw an error.
+        class QueryStatistics < MigrationObserver
+          include Gitlab::Database::SchemaHelpers
+
+          def before
+            return unless enabled?
+
+            connection.execute('select pg_stat_statements_reset()')
+          end
+
+          def record(observation)
+            return unless enabled?
+
+            observation.query_statistics = connection.execute(<<~SQL)
+              SELECT query, calls, total_time, max_time, mean_time, rows
+              FROM pg_stat_statements
+              ORDER BY total_time DESC
+            SQL
+          end
+
+          private
+
+          def enabled?
+            function_exists?(:pg_stat_statements_reset) && connection.view_exists?(:pg_stat_statements)
+          end
+        end
+      end
+    end
+  end
+end