Re: Space management for PGresult

Alvaro Herrera wrote:
> Tom Lane wrote:
> > Atsushi Ogawa <atsushi(dot)ogawa(at)gmail(dot)com> writes:
> > > The number of malloc calls at pqResultAlloc:
> > > 8.1.0 : 80542
> > > patched: 86
> >
> > > Execution time:
> > > 8.1.0 : 6.80 sec
> > > patched: 6.73 sec
> >
> > This hardly seems worth adding any complexity for ...
>
> What about memory usage? Is there a notorious difference?

Well, I measured memory usage by attached patch. An allocated(bytes)
is total amounts of allocated memory by pqResultAlloc. An unused(bytes)
is total amounts of PGresult->spaceLeft.

(1)accounts table (4 columns, 1,000,000 tuples)
malloc calls allocated(bytes) unused(bytes) execution time
--------------------------------------------------------------------------
8.1.0 80,542 164,950,016 2,946,402 6.80 sec.
patched 86 161,478,656 177,650 6.73 sec.

(2)another teble (50 columns, 100,000 tuples)
malloc calls allocated(bytes) unused(bytes) execution time
--------------------------------------------------------------------------
8.1.0 55,557 113,780,736 8,561,518 6.26 sec.
patched 86 104,855,552 83,307 6.21 sec.

The unused memory increases when the number of columns increases. The
tuple size of PGresult is proportional to the number of columns.

getAnotherTuple() at fe-protocol3.c:
--------------------------------------------------------------------------
conn->curTuple = (PGresAttValue *)
pqResultAlloc(result, nfields * sizeof(PGresAttValue), TRUE);
--------------------------------------------------------------------------

regards,

--- Atsushi Ogawa