在PostgreSQL 9.0中优化转义JSON

@H_404_0@ 我目前在Postgresql中使用这个 JSON转义函数作为未来原生 JSON支持的代表.虽然它有效,但它也限制了我们的系统性能.我该如何进行优化呢？也许某种查找数组？

CREATE OR REPLACE FUNCTION escape_json(i_text TEXT) 
RETURNS TEXT AS
$body$                                                 
DECLARE
  idx INTEGER;
  text_len INTEGER;   
  cur_char_unicode INTEGER;
  rtn_value TEXT := i_text;
BEGIN
  -- $Rev: $--
  text_len = LENGTH(rtn_value);
  idx = 1; 

  WHILE (idx <= text_len) LOOP
    cur_char_unicode = ASCII(SUBSTR(rtn_value,idx,1));

    IF cur_char_unicode > 255 THEN
      rtn_value = OVERLAY(rtn_value PLACING (E'\\u' || LPAD(UPPER(TO_HEX(cur_char_unicode)),4,'0')) FROM idx FOR 1);
      idx = idx + 5;
      text_len = text_len + 5;
    ELSE
      /* is the current character one of the following: " \ / bs ff nl cr tab */
      IF cur_char_unicode IN (34,92,47,8,12,10,13,9) THEN
        rtn_value = OVERLAY(rtn_value PLACING (E'\\' || (CASE cur_char_unicode
                                                         WHEN 34 THEN '"'
                                                         WHEN 92 THEN E'\\'
                                                         WHEN 47 THEN '/'
                                                         WHEN  8 THEN 'b'
                                                         WHEN 12 THEN 'f'
                                                         WHEN 10 THEN 'n'
                                                         WHEN 13 THEN 'r'
                                                         WHEN  9 THEN 't'
                                                          END)
                                        )
                                FROM idx FOR 1);

        idx = idx + 1;
        text_len = text_len + 1;
      END IF;
    END IF;

    idx = idx + 1;
  END LOOP;                   

  RETURN rtn_value;
END;
$body$
LANGUAGE plpgsql;