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

On Sun, Sep 10, 2017 at 9:39 PM, Peter Geoghegan <pg@bowt.ie> wrote:
> To be clear, you'll still need to set replacement_sort_tuples high
> when testing RS, to make sure that we really use it for at least the
> first run when we're expected to. (There is no easy way to have
> testing mechanically verify that we really do only have one run in the
> end with RS, but I assume that such paranoia is unneeded.)

I seem to recall that raising replacement_sort_tuples makes
replacement selection look worse in some cases -- the optimization is
more likely to apply, sure, but the heap is also bigger, which hurts.

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


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