Re: A potential memory leak on Merge Join when Sort node is not below Materialize node

On Wed, Sep 28, 2022 at 12:57 PM Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> David Rowley <dgrowleyml(at)gmail(dot)com> writes:
> > I'm wondering if the best way to fix it if doing it that way would be
> > to invent tuplesort_getdatum_nocopy() which would be the same as
> > tuplesort_getdatum() except it wouldn't do the datumCopy for byref
> > types.
>
> Yeah, perhaps. We'd need a clear spec on how long the Datum could
> be presumed good --- probably till the next tuplesort_getdatum_nocopy
> call, but that'd need to be checked --- and then check if that is
> satisfactory for nodeSort's purposes.

I am reminded of the discussion that led to bugfix commit c2d4eb1b
some years back.

As the commit message of that old bugfix notes, tuplesort_getdatum()
and tuplesort_gettupleslot() are "the odd ones out" among "get tuple"
routines (i.e. routines that get a tuple from a tuplesort by calling
tuplesort_gettuple_common()). We used to sometimes do that with
tuplesort_getindextuple() and possible other such routines, but the
need for that capability was eliminated on the caller side around the
same time as the bugfix went in.

--
Peter Geoghegan