Use multiple databases on drupal 8

Move some tables into another database.

Example:

$databases['default']['default'] = array(

  'database' => 'drupal8_default',

  'username' => 'root',

  'password' => 'THEPASSWORD',

  'host' => 'localhost',

  'port' => '3306',

  'namespace' => 'Drupal\\Core\\Database\\Driver\\mysql',

  'driver' => 'mysql',

  //Add prefix to separate databases

  'prefix' => array(

    //Use a shared database for the users (not recomended, Just for example)

    'users' => 'drupal8_shared.',

    //Move cache into another database

    'cache_bootstrap' => 'drupal8_cache.',

    'cache_config' => 'drupal8_cache.',

    'cache_container' => 'drupal8_cache.',

    'cache_data' => 'drupal8_cache.',

    'cache_default' => 'drupal8_cache.',

    'cache_discovery' => 'drupal8_cache.',

    'cache_dynamic_page_cache' => 'drupal8_cache.',

    'cache_entity' => 'drupal8_cache.',

    'cache_menu' => 'drupal8_cache.',

    'cache_render' => 'drupal8_cache.',

    'cache_toolbar' => 'drupal8_cache.',

  ),

);

//Configure shared database

$databases['shared']['default'] = array(

  'database' => 'drupal8_shared',

  'username' => 'root',

  'password' => 'THEPASSWORD',

  'host' => 'localhost',

  'port' => '3306',

  'namespace' => 'Drupal\\Core\\Database\\Driver\\mysql',

  'driver' => 'mysql',

);

//Configure cache database

$databases['cache']['default'] = array(

  'database' => 'drupal8_cache',

  'username' => 'root',

  'password' => 'THEPASSWORD',

  'host' => 'localhost',

  'port' => '3306',

  'namespace' => 'Drupal\\Core\\Database\\Driver\\mysql',

  'driver' => 'mysql',

);