Re: Progress on fast path sorting, btree index creation time

On Jan 26, 2012, at 9:32 PM, Robert Haas wrote:
> But if we want to put it on a diet, the first thing I'd probably be
> inclined to lose is the float4 specialization.  Some members of the
> audience will recall that I take dim view of floating point arithmetic
> generally, but I'll concede that there are valid reasons for using
> float8.  I have a harder time coming up with a good reason to use
> float4 - ever, for anything you care about.  So I would be inclined to
> think that if we want to trim this back a bit, maybe that's the one to
> let go.  If we want to be even more aggressive, the next thing I'd
> probably lose is the optimization of multiple sortkey cases, on the
> theory that single sort keys are probably by far the most common
> practical case.

I do find float4 to be useful, though it's possible that my understanding is flawed…

We end up using float to represent ratios in our database; things that really, honest to God do NOT need to be exact.

In most cases, 7 digits of precision (which AFAIK is what you're guaranteed with float4) is plenty, so we use float4
ratherthan bloat the database (though, since we're on 64bit hardware I guess that distinction is somewhat moot…). 

Is there something I'm missing that would make float4 useless as compared to float8?
--
Jim C. Nasby, Database Architect                   jim@nasby.net
512.569.9461 (cell)                         http://jim.nasby.net