Large HASH_SIZE with DBMS_UTILITY.GET_HASH_VALUE and performance

Question

I need to set the hash_size to quite a large value (16777216) in order to ensure uniqueness for the sets of values I ma hashing.
The examples all use much smaller values (128K).
It seems unlikely to me, but do large values for hash_size affect performance, perhaps in the amount memory used in the PGA for the hashing fucntions.

Answer 1

Hi Nijmegen
I think your problem is not related to OWB, but anyway.
If you don't change data type to char, GET_HASH_VALUE function will automatically change this data type to char in your case datetime will be changed to something like '2007.12.16' (try simple function to_char). So both values are equal '16-12-2007 13:43:55' = '2007.12.16' and '16-12-2007 16:43:55' = '2007.12.16' and you will get the same hash value. Better use POWER(2,30).
example
SELECT
DBMS_UTILITY.GET_HASH_VALUE (
TO_CHAR(TO_DATE('16-12-2007 13:43:55','dd-mm-yyyy hh24:mi:ss')),
0,
POWER(2,30)) AS x1,
DBMS_UTILITY.GET_HASH_VALUE (
TO_CHAR(TO_DATE('16-12-2007 16:43:55','dd-mm-yyyy hh24:mi:ss')),
0,
POWER(2,30)) AS x2,
DBMS_UTILITY.GET_HASH_VALUE (
'16-12-2007 13:43:55',
0,
POWER(2,30)) AS x1,
DBMS_UTILITY.GET_HASH_VALUE (
'16-12-2007 16:43:55',
0,
POWER(2,30)) AS x2,
TO_CHAR(TO_DATE('16-12-2007 13:43:55','dd-mm-yyyy hh24:mi:ss'))
FROM DUAL
Regards