Re: numeric/decimal docs bug? - Mailing list pgsql-hackers

Bruce Momjian wrote:
> Jan Wieck wrote:
> > > The hard limit is certainly no more than 64K, since we store these
> > > numbers in half of an atttypmod.  In practice I suspect the limit may
> > > be less; Jan would be more likely to remember...
> >
> >     It is arbitrary of course. I don't recall completely, have to
> >     dig into the code, but there might be some side  effect  when
> >     mucking with it.
> >
> >     The NUMERIC code increases the actual internal precision when
> >     doing multiply and divide, what  happens  a  gazillion  times
> >     when  doing higher functions like trigonometry. I think there
> >     was some connection between the max precision  and  how  high
> >     this internal precision can grow, so increasing the precision
> >     might affect the computational  performance  of  such  higher
> >     functions significantly.
>
> Oh, interesting, maybe we should just leave it alone.
   As  said, I have to look at the code. I'm pretty sure that it   currently will not use hundreds of digits internally
if  you   use  only  a  few digits in your schema. So changing it isn't   that dangerous.
 
   But who's going to write and run a regression test,  ensuring   that  the  new  high  limit can really be supported.
Ididn't   even run the numeric_big test lately, which  tests  with  500   digits  precision  at least ... and therefore
takessome time   (yawn). Increasing the number of digits used you  first  have   to  have  some  other  tool  to
generate the  test  data (I   originally used bc(1) with some scripts). Based  on  that  we   still  claim that our
systemdeals correctly with up to 1,000   digits precision.
 
   I don't like the idea of  bumping  up  that  number  to  some   higher  nonsense, claiming we support 32K digits
precisionon   exact numeric, and noone ever tested if  natural  log  really   returns  it's  result  in  that precision
insteadof a 30,000   digit precise approximation.
 
   I missed some of the discussion,  because  I  considered  the   1,000 digits already beeing complete nonsense and
droppedthe   thread. So could someone please enlighten me  what  the  real   reason  for  increasing  our  precision
is?  AFAIR  it  had   something to do with the docs. If it's just because the  docs   and  the code aren't in sync, I'd
votefor changing the docs.
 


Jan

--

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