Hi!
On Oct 31, 2009, at 11:59 AM, John David Duncan wrote:
The final result is not easy to grok. (Base 10^9?? One's
complement!? And as Sheeri said, how big on disk??) But decimal.c
is really only about 3,000 lines of code, including a 100-line
comment on the SQL standard and a 200-line test suite. GMP is more
like 50,000 lines.
GMP can do a lot more feature-wise and can handle a much larger set of
numbers then what the hand written one can.
So I'd like to make the case that it's pretty remarkable code. A
database *must* have a fixed decimal type, this design has some real
advantages over others, and there's nothing else out there that you
can really just drop in to replace it.
Looking at the code there really isn't much in the way of tests (200
lines is pretty small). One of the other things I noticed was that
when reading the comments I found that it followed the standard bug
for bug (aka... behavior wise). Is that really way someone expects?
I went and looked at the one PG is using. No limitations on size,
doesn't follow the SQL standard,...
I'm not sure that I buy the disk format being the absolute best.
Internally when it was pushed several folks pointed out other
solutions which, I have no idea, might have been better then this one.
What I do know though is that it is not that complete.
One question I ask myself... do we want to have to extend this library
to add additional functions? For that matter, what functions matter
for a database beyond comparison operations? There was a good argument
to go with the GMP since it was complete, widely used, and had a
community that worked on it. While right now? We will be stuck
extending our own library, that only we use.
There is also the question of numerical constraint, what matters?
I'm on the fence. I know this will go sometime, but I don't know when.
I hate creating upgrade paths though.
Cheers,
-Brian
I'd urge you folks to consider giving the decimal library a new
lease on life by reusing it in drizzle.
On Oct 30, 2009, at 11:44 AM, Brian Aker wrote:
Hi!
I'm working through some reference checking right now, and decided
to look at decimal. Just for those playing along at home, up until
5.0 MySQL just stored DECIMAL as a string, mostly, and did all
operations on it through normal mathematical operations. Starting
in 5.0 we switched to a library and internal developer wrote which
should mimic the SQL standard (and if you read the header in the
subject you can find out some of the absurd bits it is doing).
Would anyone care if we dropped this in favor of just using one of
the GNU based arbitrary libraries in the future? GMP perhaps
(though it is not quite the same)? I'm a minimalist when it comes
to built in types so I tend to favor this approach, but I would
like to hear from others as well.
Cheers,
-Brian
BTW any thoughts on long double over our current use of double? It
looks like it would be a mess.
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