code: public static Dialect getDialect(DataSource ds) {
  		Dialect dialect = dialectPool.get(ds);
  		if(null == dialect) {
  			synchronized (lock) {
  				dialect = dialectPool.get(ds);
  				if(null == dialect) {
  					dialect = newDialect(ds);
  					dialectPool.put(ds, dialect);
  				}
  			}
  		}
  		return dialect;
  	}
docs: 获取共享方言
  @param ds 数据源，每一个数据源对应一个唯一方言
  @return {@link Dialect}方言