Re: Let's drop two obsolete features which are bear-traps for novices

David Fetter wrote:
> On Mon, Nov 03, 2014 at 01:54:09PM +0100, Michael Banck wrote:

> > As an additional datapoint, Vitesse Data changed the DB schema from
> > NUMERIC to MONEY for their TPCH benchmark for performance reasons: "The
> > modification to data types is easy to understand -- money and double
> > types are faster than Numeric (and no one on this planet has a bank
> > account that overflows the money type, not any time soon)."[1] And
> > "Replaced NUMERIC fields representing currency with MONEY"[2].
> >
> > Not sure whether they modified/optimized PostgreSQL with respect to the
> > MONEY data type and/or how much performance that gained, so CCing CK Tan
> > as well.
>
> How does our NUMERIC type's performance compare to other systems'
> precise types? I realize that some of those systems might have
> restrictions on publishing numbers they don't authorize, but they
> might have pushed some authorized numbers if those numbers make them
> look good.

There is a real advantage of money over numeric in the performance
front. I haven't measured it, but suffice to say that money uses
integer operations which map almost directly to CPU instructions,
whereas numeric needs to decode from our varlena base-10000 digit
format, operate on digits at a time, then encode back. No matter how
much you optimize numeric, it's never going to outperform stuff that
runs practically on bare electrons. As far as I recall, some TPCH
queries run aggregations on currency columns.

Now, whether this makes a measurable difference or not in TPCH terms, I
have no idea.

--
Álvaro Herrera http://www.2ndQuadrant.com/
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