Re: [HACKERS] regression bigtest needs very long time

wieck@debis.com (Jan Wieck) writes:
>> >     We certainly should think about a general speedup of NUMERIC.
>>
>> How would we do that?  I assumed it was already pretty optimized.
>
>    The  speedup  (I expect) results from the fact that the inner
>    loops of add,  subtract  and  multiply  will  then  handle  4
>    decimal digits per cycle instead of one! Doing a
>
>        1234.5678 + 2345.6789
>
>    then needs 2 internal cycles instead of 8. And
>
>        100.123 + 12030.12345
>
>    needs  4  cycles instead of 10 (because the decimal point has
>    the same meaning in base  10000  the  last  value  is  stored
>    internally  as  short  ints 1, 2030, 1234, 5000). This is the
>    worst case and it still saved 60% of the innermost cycles!

The question, though, becomes what percentage of operations on a 
NUMERIC field are arithmetic, and what percentage are storage/retrieval.

For databases that simply store/retrieve data, your "optimization" will have
the effect of significantly increasing format conversion overhead.  With a
512-byte table, four packed-decimal digits can be converted in two
primitive operations, but base-10000 will require three divisions, 
three subtractions, four additions, plus miscellaneous data shuffling.
-Michael Robinson