| From: | Peter Geoghegan <pg(at)heroku(dot)com> |
|---|---|
| To: | Robert Haas <robertmhaas(at)gmail(dot)com> |
| Cc: | Heikki Linnakangas <hlinnakangas(at)vmware(dot)com>, Noah Misch <noah(at)leadboat(dot)com>, Marti Raudsepp <marti(at)juffo(dot)org>, Stephen Frost <sfrost(at)snowman(dot)net>, Greg Stark <stark(at)mit(dot)edu>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Thom Brown <thom(at)linux(dot)com>, Pg Hackers <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: B-Tree support function number 3 (strxfrm() optimization) |
| Date: | 2014-09-03 01:13:16 |
| Message-ID: | CAM3SWZSoRvJ+-Bh4B_ux3Hgx4Vsep3YWbMTveCguCJbhcmKHnw@mail.gmail.com |
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| Lists: | pgsql-hackers |
On Tue, Sep 2, 2014 at 12:22 PM, Robert Haas <robertmhaas(at)gmail(dot)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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