Re: Re: patch: fix performance problems with repated decomprimation of varlena values in plpgsql

Robert Haas <robertmhaas(at)gmail(dot)com> writes:
> On Tue, Jan 25, 2011 at 10:03 AM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>> The arguments that were made against this were about maintenance costs
>> and code footprint. Claims about performance are not really relevant,
>> especially when they're entirely unsupported by evidence.

> How much evidence do you need to the effect that detoasting a value
> that's never used will hurt performance?

I agree that at some microscopic level it will cost something. What's
not been shown is that there's any significant cost in any real-world
use pattern. As Pavel said upthread, the main thing here is to get rid
of cases where there are many many repeated detoastings. Adding an
occasional detoast that wouldn't have happened before is a good tradeoff
for that. To convince me that we should contort the code to go further,
you need to show that that's more than a negligible cost.

regards, tom lane