Re: Inlining comparators as a performance optimisation

Peter Geoghegan wrote:
> On 29 November 2011 15:31, Bruce Momjian <bruce@momjian.us> wrote:
> > These are exciting advanced you are producing and I am hopeful we can
> > get this included in Postgres 9.2.
> 
> Thanks Bruce.
> 
> >I have mentioned already that I
> > think parallelism is the next big Postgres challenge, and of course, one
> > of the first areas for parallelism is sorting.
> 
> I'm not sure that sorting has that much to recommend it as an initial
> target of some new backend parallelism other than being easy to
> implement. I've observed the qsort_arg specialisations in this patch
> out-perform stock qsort_arg by as much as almost 3 times. However, the
> largest decrease in a query's time that I've observed was 45%, and
> that was for a contrived worst-case for quicksort, but about 25% is
> much more typical of queries similar to the ones I've shown, for more
> normative data distributions. While that's a respectable gain, it
> isn't a paradigm shifting one, and it makes parallelising qsort itself
> for further improvements quite a lot less attractive - there's too
> many other sources of overhead.

Agreed.  I think your improvements make it likely we will address not
address sort parallelism first.

With all the improvements coming in Postgres 9.2, we might need to look
at I/O parallelism first.

--  Bruce Momjian  <bruce@momjian.us>        http://momjian.us EnterpriseDB
http://enterprisedb.com
 + It's impossible for everything to be true. +