Remove the comment on the countereffectiveness of large shared_buffers on Windows

Hello,

> From: pgsql-hackers-owner@postgresql.org
> [mailto:pgsql-hackers-owner@postgresql.org] On Behalf Of Magnus Hagander
> On Wed, Aug 24, 2016 at 4:35 AM, Tsunakawa, Takayuki
> <tsunakawa.takay@jp.fujitsu.com> wrote:
>     As a similar topic, I wonder whether the following still holds true,
> after many improvements on shared buffer lock contention.
>
>     https://www.postgresql.org/docs/devel/static/runtime-config-re
> source.html
>
>             "The useful range for shared_buffers on Windows systems
> is generally from 64MB to 512MB."
>
>
>
>
> Yes, that may very much be out of date as well. A good set of benchmarks
> around that would definitely be welcome.


I'd like to propose the above-mentioned comment from the manual.  The patch is attached.

I ran read-only and read-write modes of pgbench, and could not see any apparent decrease in performance when I
increasedshared_buffers.  The scaling factor is 200, where the database size is roughly 3GB.  I ran the benchmark on my
Windows10 PC with 6 CPU cores and 16GB of RAM.  The database and WAL is stored on the same HDD. 

<<Test batch file>>
@echo off
for %%s in (256MB 512MB 1GB 2GB 4GB) do (
  pg_ctl -w -o "-c shared_buffers=%%s" start
  pgbench -c18 -j6 -T60 -S bench >> g:\b.txt 2>&1
  pg_ctl -t 3600 stop
)

<<Select-only (with -S)>>
shared_buffers  tps
256MB  63056
512MB  63918
1GB  65520
2GB  66840
4GB  68270

<<Read-write (without -S)>>
shared_buffers  tps
256MB  1138
512MB  1187
1GB  1571
2GB  1650
4GB  1598

Regards
Takayuki Tsunakawa