Re: Minor performance improvement in transition to external sort

On 6 February 2014 18:21, Jeff Janes <jeff.janes@gmail.com> wrote:
> On Tue, Feb 4, 2014 at 2:22 PM, Jeremy Harris <jgh@wizmail.org> wrote:
>>
>> The attached patch replaces the existing siftup method for heapify with
>> a siftdown method. Tested with random integers it does 18% fewer
>> compares and takes 10% less time for the heapify, over the work_mem
>> range 1024 to 1048576.
>
>
> Thanks for working on this.

+1

Your patch isn't linked properly from the CF manager though.

If you like patches like this then there's a long(er) list of
optimizations already proposed previously around sorting. It would be
good to have someone work through them for external sorts. I believe
Noah is working on parallel internal sort (as an aside).

There's also an optimization possible for merge joins where we use the
output of the first sort as an additional filter on the second sort.
That can help when we're going to join two disjoint tables.

-- Simon Riggs                   http://www.2ndQuadrant.com/PostgreSQL Development, 24x7 Support, Training & Services