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

On Wed, Jan 19, 2011 at 12:10:16PM -0500, Tom Lane wrote:
> Robert Haas <robertmhaas(at)gmail(dot)com> writes:
> > On Tue, Jan 18, 2011 at 5:22 PM, Pavel Stehule <pavel(dot)stehule(at)gmail(dot)com> wrote:
> >> opinion isn't strong in this topic. One or twenty useless detoasting
> >> isn't really significant in almost use cases (problem is thousands
> >> detoasting).
>
> > Yeah. Many-times-repeated detoasting is really bad, and this is not
> > the only place in the backend where we have this problem. :-(
>
> Yeah, there's been some discussion of a more general solution, and I
> think I even had a trial patch at one point (which turned out not to
> work terribly well, but maybe somebody will have a better idea someday).
> In the meantime, the proposal at hand seems like a bit of a stop-gap,
> which is why I'd prefer to see something with a very minimal code
> footprint. Detoast at assignment would likely need only a few lines
> of code added in a single place.

What qualifies a patch as stop-gap scale? Pavel's patch is ~60 lines.

If adding PLpgSQL_var.should_be_detoasted is your main pain point, testing
VARATT_IS_EXTENDED there might be the least-harmful way to avoid it. Saving a
few more lines by moving the work to exec_assign_value probably does not justify
the associated performance regressions Pavel has cited.

nm