On 6/18/09, Simon Riggs <simon@2ndquadrant.com> wrote:
> On Tue, 2009-06-16 at 10:23 -0400, Tom Lane wrote:
> > Speaking of which, what about some performance numbers? Like Heikki,
> > I'm quite suspicious of whether there is any real-world gain to be had
> > from this approach.
>
>
> It has been "lore" for some time that VARCHAR is cheaper than
> VARCHAR(n), so I'm looking forward to this improvement as a real-world
> gain. (If done right).
>
> I've looked at the code and the thing that bothers me is that I can't
> see where or why bcTruelen would be called more often for VARCHAR(n)
> than it would be for VARCHAR, on a Select/Sort only workload.
I'd guess plain VARCHAR simply does not have blanks at the end,
so Truelen is cheap.
> Are we tuning the right thing? Is there some code we can completely
> avoid?
>
> If not, does this mean it is a generic effect? Does this imply that
> NUMERIC(n) is somehow worse than NUMERIC? etc..
Probably not. For numeric the (n) seems to be only checked input time.
--
marko