| From: | Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com> |
|---|---|
| To: | Peter Geoghegan <peter(at)2ndquadrant(dot)com> |
| Cc: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, PG Hackers <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: Inlining comparators as a performance optimisation |
| Date: | 2011-09-21 06:51:32 |
| Message-ID: | 4E798974.8030801@enterprisedb.com |
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| Lists: | pgsql-hackers |
On 21.09.2011 02:53, Peter Geoghegan wrote:
> C stdlib quick-sort time elapsed: 2.092451 seconds
> Inline quick-sort time elapsed: 1.587651 seconds
>
> Does *that* look attractive to you?
Not really, to be honest. That's a 25% speedup in pure qsorting speed.
How much of a gain in a real query do you expect to get from that, in
the best case? There's so many other sources of overhead that I'm afraid
this will be lost in the noise. If you find a query that spends, say,
50% of its time in qsort(), you will only get a 12.5% speedup on that
query. And even 50% is really pushing it - I challenge you to find a
query that spends any significant amount of time qsorting integers.
--
Heikki Linnakangas
EnterpriseDB http://www.enterprisedb.com
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