Re: Which qsort is used

Qingqing,

On 12/13/05 10:28 AM, "Qingqing Zhou" <zhouqq(at)cs(dot)toronto(dot)edu> wrote:

> http://www.cs.toronto.edu/~zhouqq/postgresql/sort/sort.html
>
> The source tar ball and linux 2.4G gcc 2.96 test results is on the page.
> There is a clear loser glibc, not sure qsortB or qsortG which is better.

Great stuff - thanks for doing this.

From the results, it's clear that the scale test makes a huge difference in
the relative performance. I'm wondering if it's an L2 cache effect, as it
seems to occur in that range.

Overall - I'd say that the BSD routine is showing the best overall results
when the scale test is included. The qsortG routine has some significantly
better performance in certain cases at smaller sort set sizes - it could
probably be improved for better L2 use, but BSD is already there.

Based on this it seems like we should expose the option to choose the BSD
qsort routine at configure time.

- Luke