Re: [HACKERS] The case for removing replacement selection sort

On Mon, Sep 11, 2017 at 11:47 AM, Tomas Vondra
<tomas.vondra@2ndquadrant.com> wrote:
> The question is what is the optimal replacement_sort_tuples value? I
> assume it's the number of tuples that effectively uses CPU caches, at
> least that's what our docs say. So I think you're right it to 1B rows
> may break this assumption, and make it perform worse.
>
> But perhaps the fact that we're testing with multiple work_mem values,
> and with smaller data sets (100k or 1M rows) makes this a non-issue?

I am not sure that's the case -- I think that before Peter's changes
it was pretty easy to find cases where lowering work_mem made sorting
ordered data go faster.

But I could easily be wrong.

-- 
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company


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