Add graphs and retention metrics to admin dashboard (#16829)

app/lib/admin/metrics/dimension/space_usage_dimension.rb

@@ -0,0 +1,70 @@
+# frozen_string_literal: true
+
+class Admin::Metrics::Dimension::SpaceUsageDimension < Admin::Metrics::Dimension::BaseDimension
+  include Redisable
+  include ActionView::Helpers::NumberHelper
+
+  def key
+    'space_usage'
+  end
+
+  def data
+    [postgresql_size, redis_size, media_size]
+  end
+
+  private
+
+  def postgresql_size
+    value = ActiveRecord::Base.connection.execute('SELECT pg_database_size(current_database())').first['pg_database_size']
+
+    {
+      key: 'postgresql',
+      human_key: 'PostgreSQL',
+      value: value.to_s,
+      unit: 'bytes',
+      human_value: number_to_human_size(value),
+    }
+  end
+
+  def redis_size
+    value = redis_info['used_memory']
+
+    {
+      key: 'redis',
+      human_key: 'Redis',
+      value: value.to_s,
+      unit: 'bytes',
+      human_value: number_to_human_size(value),
+    }
+  end
+
+  def media_size
+    value = [
+      MediaAttachment.sum(Arel.sql('COALESCE(file_file_size, 0) + COALESCE(thumbnail_file_size, 0)')),
+      CustomEmoji.sum(:image_file_size),
+      PreviewCard.sum(:image_file_size),
+      Account.sum(Arel.sql('COALESCE(avatar_file_size, 0) + COALESCE(header_file_size, 0)')),
+      Backup.sum(:dump_file_size),
+      Import.sum(:data_file_size),
+      SiteUpload.sum(:file_file_size),
+    ].sum
+
+    {
+      key: 'media',
+      human_key: I18n.t('admin.dashboard.media_storage'),
+      value: value.to_s,
+      unit: 'bytes',
+      human_value: number_to_human_size(value),
+    }
+  end
+
+  def redis_info
+    @redis_info ||= begin
+      if redis.is_a?(Redis::Namespace)
+        redis.redis.info
+      else
+        redis.info
+      end
+    end
+  end
+end