| From: | Peter Geoghegan <pg(at)heroku(dot)com> |
|---|---|
| To: | Robert Haas <robertmhaas(at)gmail(dot)com> |
| Cc: | Andrew Gierth <andrew(at)tao11(dot)riddles(dot)org(dot)uk>, 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>, Pg Hackers <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: B-Tree support function number 3 (strxfrm() optimization) |
| Date: | 2015-01-21 00:07:53 |
| Message-ID: | CAM3SWZRe5-JizUdvHRiJuZEQY2Va-ddREPEMhosnedvdDVFuJQ@mail.gmail.com |
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| Lists: | pgsql-hackers |
On Tue, Jan 20, 2015 at 3:57 PM, Peter Geoghegan <pg(at)heroku(dot)com> wrote:
> It's certainly possible to fix Andrew's test case with the attached.
> I'm not sure that that's the appropriate fix, though: there is
> probably a case to be made for not bothering with abbreviation once
> we've read tuples in for the final merge run. More likely, the
> strongest case is for storing the abbreviated keys on disk too, and
> reading those back.
Maybe not, though: An extra 8 bytes per tuple on disk is not free.
OTOH, if we're I/O bound on the final merge, as we ought to be, then
recomputing the abbreviated keys could make sense, since there may
well be an idle CPU core anyway.
--
Peter Geoghegan
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