Enable verbose query logging

This backports the rails/rails#26815
and enables that for non-Rails5 and non-production environments.

config/initializers/active_record_verbose_query_logs.rb

@@ -0,0 +1,54 @@
+# frozen_string_literal: true
+
+# This is backport of https://github.com/rails/rails/pull/26815/files
+# Enabled by default for every non-production environment
+
+module ActiveRecord
+  class LogSubscriber
+    module VerboseQueryLogs
+      def debug(progname = nil, &block)
+        return unless super
+
+        log_query_source
+      end
+
+      def log_query_source
+        source_line, line_number = extract_callstack(caller_locations)
+
+        if source_line
+          if defined?(::Rails.root)
+            app_root = "#{::Rails.root}/".freeze
+            source_line = source_line.sub(app_root, "")
+          end
+
+          logger.debug("  ↳ #{source_line}:#{line_number}")
+        end
+      end
+
+      def extract_callstack(callstack)
+        line = callstack.find do |frame|
+          frame.absolute_path && !ignored_callstack(frame.absolute_path)
+        end
+
+        offending_line = line || callstack.first
+        [
+          offending_line.path,
+          offending_line.lineno,
+          offending_line.label
+        ]
+      end
+
+      LOG_SUBSCRIBER_FILE = ActiveRecord::LogSubscriber.method(:logger).source_location.first
+      RAILS_GEM_ROOT = File.expand_path("../../../..", LOG_SUBSCRIBER_FILE) + "/"
+      APP_CONFIG_ROOT = File.expand_path("..", __dir__) + "/"
+
+      def ignored_callstack(path)
+        path.start_with?(APP_CONFIG_ROOT, RAILS_GEM_ROOT, RbConfig::CONFIG["rubylibdir"])
+      end
+    end
+
+    unless Gitlab.rails5?
+      prepend(VerboseQueryLogs) unless Rails.env.production?
+    end
+  end
+end