找到根目录 config/ config_global.php  文件

增加
/*读写分离*/

  $_config['db']['1']['slave']['1']['dbhost'] = '数据库地址';
  $_config['db']['1']['slave']['1']['dbuser'] = '数据库密用户名';
  $_config['db']['1']['slave']['1']['dbpw'] = '数据库密码';
  $_config['db']['1']['slave']['1']['dbcharset'] = 'utf8';
  $_config['db']['1']['slave']['1']['pconnect'] = '0';
  $_config['db']['1']['slave']['1']['dbname'] = '数据库名称';
  $_config['db']['1']['slave']['1']['tablepre'] = 'pre_';
  $_config['db']['1']['slave']['1']['weight'] = '100'; //权重：数据越大权重越高

/*增加第二台读写分离*/

  $_config['db']['1']['slave']['2']['dbhost'] = '数据库地址';
  $_config['db']['1']['slave']['2']['dbuser'] = '数据库密用户名';
  $_config['db']['1']['slave']['2']['dbpw'] = '数据库密码';
  $_config['db']['1']['slave']['2']['dbcharset'] = 'utf8';
  $_config['db']['1']['slave']['2']['pconnect'] = '0';
  $_config['db']['1']['slave']['2']['dbname'] = '数据库名称';
  $_config['db']['1']['slave']['2']['tablepre'] = 'pre_';
  $_config['db']['1']['slave']['2']['weight'] = '100'; //权重：数据越大权重越高

//启用从服务器的开关
$_config['db']['slave'] = true;

$_config['db']['common']['slave_except_table'] = 'common_session, common_member';