Performance of regexp_replace vs translate in Oracle?

Question

For simple things is it better to use the translate function on the premise that it is less CPU intensive or is regexp_replace the way to go?

Answer 1

For SQL, I tested this with the following script:

set timing on

select sum(length(x)) from (
  select translate('()', '()[]', '----') x
  from (
    select *
    from dual
    connect by level <= 2000000
  )
);

select sum(length(x)) from (
  select regexp_replace('[()]', '[\(\)\[]|\]', '-', 1, 0) x
  from (
    select *
    from dual
    connect by level <= 2000000
  )
);

and found that the performance of translate and regexp_replace were almost always the same, but it could be that the cost of the other operations is overwhelming the cost of the functions I'm trying to test.

Next, I tried a PL/SQL version:

set timing on

declare
  x varchar2(100);
begin
  for i in 1..2500000 loop
    x := translate('()', '()[]', '----');
  end loop;
end;
/

declare
  x varchar2(100);
begin
  for i in 1..2500000 loop
    x := regexp_replace('[()]', '[\(\)\[]|\]', '-', 1, 0);
  end loop;
end;
/

Here the translate version takes just under 10 seconds, while the regexp_replace version around 0.2 seconds -- around 2 orders of magnitude faster(!)

Based on this result, I will be using regular expressions much more often in my performance critical code -- both SQL and PL/SQL.