Reduce the number of indexes on the node_field_* tables

    'indexes' => array(
      'node_changed' => array('changed'),
      'node_created' => array('created'),
      'node_default_langcode' => array('default_langcode'),
      'node_langcode' => array('langcode'),
      'node_frontpage' => array('promote', 'status', 'sticky', 'created'),
      'node_status_type' => array('status', 'type', 'nid'),
      'node_title_type' => array('title', array('type', 4)),
      'node_type' => array(array('type', 4)),
      'nid' => array('nid'),
      'vid' => array('vid'),
      'uid' => array('uid'),
    ),

That's too much. Indexes have a cost, inserts and updates get slower. Some of them are useless, like the separate index on nid, indexes also always work on parts of them. Others are unnecessary or inefficent or can be combined.