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Re: [NOVICE] Postgres storing time in strange manner

From: Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us>
To: Thomas Lockhart <lockhart(at)fourpalms(dot)org>
Cc: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>,Ron Johnson <ron(dot)l(dot)johnson(at)cox(dot)net>, pgsql-bugs(at)postgresql(dot)org
Subject: Re: [NOVICE] Postgres storing time in strange manner
Date: 2002-09-18 00:03:40
Message-ID: 200209180003.g8I03eQ07965@candle.pha.pa.us (view raw or flat)
Thread:
Lists: pgsql-bugs
Thomas Lockhart wrote:
> ...
> > > > Hard to imagine why anyone would want such an optimization.  How much
> > > > faster could it possibly be?
> > > Back in ye bad olde days, there was probably an order-of-magnitude
> > > difference between the speed of a float multiply and that of a float
> > > divide; so this used to be a pretty standard sort of optimization.
> > > I can remember doing the equivalent thing by hand in source code.
> > > On modern hardware I doubt it makes much difference...
> 
> The speed difference is still there; you can't do a divide with one pass
> through a barrel shifter, which is how the multiply operations were sped
> up. I vaguely recall something like a 40:1 ratio on a 604 PowerPC but
> that may not be accurate, or may be for integers which have similar
> issues.

Wow, 40:1 is a major difference.

> > And you would have to do a heck of a lot of them to see a difference.
> 
> ?? Some applications *do* do a heck of a lot of them ;)

Yep, I am sure.  The question is whether there is ever a reason to use
such a flag on the database code.  My guess is no.

-- 
  Bruce Momjian                        |  http://candle.pha.pa.us
  pgman(at)candle(dot)pha(dot)pa(dot)us               |  (610) 359-1001
  +  If your life is a hard drive,     |  13 Roberts Road
  +  Christ can be your backup.        |  Newtown Square, Pennsylvania 19073

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