> -----Ursprüngliche Nachricht-----
> Von: Tom Lane [mailto:tgl@sss.pgh.pa.us]
> Gesendet: Montag, 29. Mai 2017 10:19
> An: Klaus P. Pieper
> Cc: pgsql-admin@postgresql.org
> Betreff: Re: [ADMIN] pgbench Windows outperforms Debian in Write tests
> while Debian is faster in SELECT only tests
>
> "Klaus P. Pieper" <kpi6288@gmail.com> writes:
> > How can Windows outperform Debian by a factor of 2?
>
> Are you sure you have Windows configured to fsync properly?
> Not waiting for writes to hit disk would be a really easy explanation for a
> discrepancy of this kind.
It seems that it is indeed related to the wal_sync_method settings.
Results for 1 client read / write:
Option Windows Debian
fdatasync 340 150
fsync 125 90
open_datasync 360 160
fsync_writethrough 115 n/a
open_sync n/a 90
fsync = off 360 400
The result setting fsync=off shows that the maximum performance of the Debian syste is above Windows.
However, with fsync=on, Windows still outperforms the Debian system with all options.
In addition, the results on the Windows system with “fsync = off” are the same as “wal_sync_method = open_datasync”
What does this mean?
- Is the Windows system “better” than the Debian system?
- Or is the underlying filesystem on the Windows system less safe?
- Or is the Windows system better integrated with the Hyper-V host?
The Windows systems reports that the write cache is switched on for the virtual disk. It is however not possible to switch is off.
Thanks
Klaus