Re: Using quicksort for every external sort run

On Thu, Mar 10, 2016 at 1:40 PM, Tomas Vondra <tomas(dot)vondra(at)2ndquadrant(dot)com>
wrote:
> I was thinking about running some benchmarks on this patch, but the
> thread is pretty huge so I want to make sure I'm not missing something
> and this is indeed the most recent version.

I also ran some preliminary benchmarks just before FOSDEM and intend to get
back to in after running different benchmarks. These are preliminary
because it was only a single run and on a machine that wasn't dedicated for
benchmarks. These were comparing the quicksort-all-runs patch against HEAD
at the time without the memory management optimizations which I think are
independent of the sort algorithm.

It looks to me like the interesting space to test is on fairly small
work_mem compared to the data size. There's a general slowdown on 4MB-8MB
work_mem when the data set is more than a gigabyte but but even in the
worst case it's only a 30% slowdown and the speedup in the more realistic
scenarios looks at least as big.

I want to rerun these on a dedicated machine and with trace_sort enabled so
that we can see how many merge passes were actually happening and how much
I/O was actually happening.

--
greg