Hi,

How can i compensate the oracle hash function for

parallel_enable(partition myCursor by hash(Some_Key))

Because Some_Key is already a good ID to dispatch to the table
functions.
For a bulk i have e.g. #10 Some_Key values with nearly the same
#number of records per Some_Key value.
This means a balanced load distribution to the parallel pipelined
table function instances.
However oracle requiring hash(Some_Key) undermines the load balancing
(the same for range(Some_Key)).

So i would like to translate Some_Key to a value, that after
hash(Some_Key) results in ID (Some_Key) used for dispatch - some kind
of anti-hash.

So functionally speaking it ends up in

parallel_enable(partition myCursor by hash(antihash(Some_Key)))

.... which effectively is

parallel_enable(partition myCursor by SomeKey)


What's the anti-hash (inverse) function, which compensates for
hash(Some_Key)?

- many thanks!

regards,
Frank

On Wednesday, January 25, 2012 11:24:58 AM UTC+1, Frank Bergemann wrote:
Why is it the same for range partitioning?

Hash functions do not have an inverse function because they are not injections.

http://en.wikipedia.org/wiki/Inverse_function

Kind regards

robert

Hi Robert,

On 25 Jan., 17:40, Robert Klemme <shortcut... (AT) googlemail (DOT) com> wrote:
I have to correct myself - i don't need an inverse "function" in terms
of mathematics.
That is not possible, because hashing compacts the number space
resulting in (minimized) clashing.
So it is not n:1 in forward direction and 1:n in backwards direction -
so no function.
But i just need *some* back-mapping.
And i found a way:
Create a look-up table for the forward mapping and use it in inverse
direction (fortunately i have only a small set of input values).

best regards,
Frank

On 26 Jan., 09:21, Frank Bergemann <FBergem... (AT) web (DOT) de> wrote:
sorry, there's a type: it should have been:

So it is n:1 in forward direction and 1:n in backwards direction - so
no function.

best regards,
Frank

On 26 Jan., 09:21, Frank Bergemann <FBergem... (AT) web (DOT) de> wrote:
ups! there's a typo - it should have been

So it is n:1 in forward direction and 1:n in backwards direction - so
no function.

best regards,
Frank