Magnus prepared a trivial patch which added the O_SYNC flag for windows
and mapped it to FILE_FLAG_WRITE_THROUGH in win32_open.c.  We pg_benched
it and here are the results of our test on my WinXP workstation on a 10k

Settings were pgbench -t 100 -c 10.

fsync = off: 
~ 280 tps

fsync on, WAL=fsync:
~ 35 tps 

fsync on, WAL=open_sync write cache policy on:
~ 240 tps

fsync on, WAL=open_sync write cache policy off:
~ 80 tps

80 tps, btw, is about the results I'd expect from linux on this
hardware.  Also, the open_sync method plays much nicer with RAID
devices, but it would need some more rigorous testing before I'd
personally certify it as safe.  As an aside, it doesn't look like the
open_sync can be trusted with write caching policy on the disk (the
default), and that's worth noting.  


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