Problem w. hash-value calculation for CLOB with DBMS_UTILITY.GET_HASH_VALUE

Question

Hello Oracle-Experts,
I had to calculate hash-values for a corrorponding CLOB-field (see my post 'Buffer to small ORA-22835 error after migration from 9i to 10g' in forum 'database general').
I calculate the hash-values with the DBMS_UTILITY.GET_HASH_VALUE, e.g:
     SQL> SELECT DBMS_UTILITY.GET_HASH_VALUE(LPAD('X',3998,'X'),1,POWER(2,30)) FROM dual;
     DBMS_UTILITY.GET_HASH_VALUE(LPAD('X',3998,'X'),1,POWER(2,30))
     1053896858
Because the calculation failed with 10g I had taken a closer look at this function and realised the following results:
VALUE                                             DBMS_UTILITY.GET_HASH_VALUE(VALUE,1,POWER(2,30))
LPAD('X',3997,'X') 557754150
LPAD('X',3998,'X')      1053896858
LPAD('X',3999,'X')          888036750
LPAD('X',4000,'X') 162062978
LPAD('X',4001,'X')          162062978
LPAD('X',4002,'X') 162062978
LPAD('X',10000,'X') 162062978
It seems to me that I can't use this function for clob-values with a length greater than 4000 characters because of collisions. Maybe someone with experience
can give me a hint to handle this problem. Worst case i had to write my own CLOB_2_HASH function.
TIA + Best regards
Matthias

Answer 1

Yeah, the 4000-byte limit would be a factor in working CLOBs. I if you only had 4000 bytes you would not need a CLOB in the first place.
If you don't find something better then writing your own function might be the thing to do.