old_contents: from __future__ import absolute_import
  from django.apps import AppConfig
  from django.conf import settings
  from django.core.checks import Error, register
  
  
  class SQLDBAppConfig(AppConfig):
      name = 'corehq.sql_db'
  
  
  default_app_config = 'corehq.sql_db.SQLDBAppConfig'
  
  
  @register()
  def custom_db_checks(app_configs, **kwargs):
      errors = []
      custom_db_settings = [
          'WAREHOUSE_DATABASE_ALIAS',
          'SYNCLOGS_SQL_DB_ALIAS'
      ]
      for setting in custom_db_settings:
          default = getattr(settings, setting) == 'default'
          custom =  not default and getattr(settings, setting) in settings.DATABASES
          if not (default or custom):
              errors.append(
                  Error('settings.{} should either be "default" for a default database'
                        'or a valid database defined in settings.DATABASES'.format(setting))
              )
          if custom and not settings.USE_PARTITIONED_DATABASE:
              errors.append(
                  Error('A custom database can\'tbe used without a partitioned database.'
                        'settings.USE_PARTITIONED_DATABASE must be True if '
                        'settings.{} is set to a custom database.'.format(setting))
              )
      return errors
  
new_contents: from __future__ import absolute_import
  from django.apps import AppConfig
  from django.conf import settings
  from django.core.checks import Error, register
  
  
  class SQLDBAppConfig(AppConfig):
      name = 'corehq.sql_db'
  
  
  default_app_config = 'corehq.sql_db.SQLDBAppConfig'
  
  
  @register()
  def custom_db_checks(app_configs, **kwargs):
      errors = []
      custom_db_settings = [
          'WAREHOUSE_DATABASE_ALIAS',
          'SYNCLOGS_SQL_DB_ALIAS'
      ]
      for setting in custom_db_settings:
          default = getattr(settings, setting) == 'default'
          custom = not default and getattr(settings, setting) in settings.DATABASES
          if not (default or custom):
              errors.append(
                  Error('settings.{} should either be "default" for a default database'
                        'or a valid database defined in settings.DATABASES'.format(setting))
              )
      return errors
  
subject: remove restriction on 'custom' databases