Horton

Re: Inlining comparators as a performance optimisation

Simon Riggs <simon@2ndquadrant.com>

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From: Simon Riggs <simon@2ndQuadrant.com>
To: Heikki Linnakangas <heikki.linnakangas@enterprisedb.com>
Cc: Peter Geoghegan <peter@2ndquadrant.com>, Tom Lane <tgl@sss.pgh.pa.us>, PG Hackers <pgsql-hackers@postgresql.org>
Date: 2011-09-21T07:01:11Z
Lists: pgsql-hackers

Commits

Same data as JSON: GET /api/v1/messages/:b64id/commits the thread's linked commits as JSON, with link sources. API reference →

  1. Speed up conversion of signed integers to C strings.

  2. Remove some unnecessary tests of pgstat_track_counts.

  3. Remove cvs keywords from all files.

  4. Code cleanup for function prototypes: change two K&R-style prototypes

  5. Use Min() instead of min() in qsort, for consistency and to avoid

  6. pgindent run for 8.2.

  7. Switch over to using our own qsort() all the time, as has been proposed

On Wed, Sep 21, 2011 at 7:51 AM, Heikki Linnakangas
<heikki.linnakangas@enterprisedb.com> wrote:
> 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.

How about almost every primary index creation?

Don't really see a reason for the negativity here. If you use that
argument no performance gain is worth it because all workloads are
mixed.

This is a marvellous win, a huge gain from a small, isolated and
easily tested change. By far the smallest amount of additional code to
sorting we will have added and yet one of the best gains.

-- 
 Simon Riggs                   http://www.2ndQuadrant.com/
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