Tom Lane wrote:
> Obviously, if you are transporting the dump across platforms then that
> may be an impossibility. In that case you use a text dump and accept
> that you get an approximation.
That's something that I've been meaning to ask about, but you all
seemed so sure of yourself. What you are essentially saying is that no
one aside from the server itself is allowed to get full precision. That
seems like a strange decision to make.
> But there should be a way to ensure that
> you can have a lossless dump of whatever strange FP format your server
> may use, as long as you are restoring onto a similar machine.
>
Personally (and I know my opinion "doesn't count"), I find the "similar
machine" requirement a bit hard. It is usually accepted for HA or live
load balancing, but is really inappropriate for backups or data
transfers. Just my humble opinion.
> If there is a guaranteed-reversible transform between the ARM FP format
> and IEEE format, then I'd be interested in hacking things the way you
> suggest
I find it highly likely that there will be. After all, the ARM format
was not designed to be better packed than IEEE, just easier to hardware
implement in an efficient way. However
> --- but what I suspect is that such a conversion must lose
> either range or precision. There are only so many bits in a double.
>
Like I said elsewhere, a 64bit FP only has 64bits, but there is nothing
constraining us to export a 64bit number to 64bits.
> regards, tom lane
>
What I'm worried about in that regard is about other platforms that PG
may be running on. Like I said above, I'm fairly sure (will get the
specs and make sure) that there shouldn't be a problem in exporting ARM
FP into 64bit IEEE with no loss at all. This says nothing, however,
about other platforms. Unless we map all cases, we had better choose an
export format that is capable of extension.
Shachar