| From: | Andrew Gierth <andrew(at)tao11(dot)riddles(dot)org(dot)uk> |
|---|---|
| To: | Peter Geoghegan <pg(at)heroku(dot)com> |
| Cc: | Robert Haas <robertmhaas(at)gmail(dot)com>, 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 09:47:54 |
| Message-ID: | 87h9vklbgp.fsf@news-spur.riddles.org.uk |
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| Lists: | pgsql-hackers |
>>>>> "Peter" == Peter Geoghegan <pg(at)heroku(dot)com> writes:
Peter> You'll probably prefer the attached. This patch works by
Peter> disabling abbreviation, but only after writing out runs, with
Peter> the final merge left to go. That way, it doesn't matter when
Peter> abbreviated keys are not read back from disk (or regenerated).
This seems tolerable to me for a quick fix. The merits of storing the
abbreviation vs. re-abbreviating on input can be studied later.
Peter> I believe this bug was missed because it only occurs when there
Peter> are multiple runs, and not in the common case where there is one
Peter> big initial run that is found already sorted when we reach
Peter> mergeruns().
Ah, yes, there is an optimization for the one-run case which bypasses
all further comparisons, hiding the problem.
--
Andrew (irc:RhodiumToad)
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