On Tue, Sep 2, 2014 at 12:22 PM, Robert Haas <robertmh...@gmail.com> wrote:
> Most places that use a SortSupportData initialize ssup.position
> explicitly, but tuplesort_begin_datum() doesn't.  That's an
> inconsistency that should be fixed, but I'm not sure which direction
> is best.

I'm not sure what you mean. tuplesort_begin_datum() only
uses/initializes the Tuplesortstate.onlyKey field, and in fact that
did have its ssup.position initialized to zero in the last revision.
This indicates that we should not apply the optimization, because:

 * Conversion to abbreviated representation infeasible in the Datum case.
 * It must be possible to subsequently fetch original datum values within
 * tuplesort_getdatum(), which would require special-case preservation of
 * original values that we prefer to avoid.
state->onlyKey->position = sortKeyOther;

Peter Geoghegan

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