> > What version exactly was this? There was some changes in
> 8.0.2 in this
> > area on win32. The default sync method was also changed at
> this point.
>
> "PostgreSQL 8.0.2 on i686-pc-mingw32, compiled by GCC gcc.exe
> (GCC) 3.4.2 (mingw-special)"
There we go. That explains it - you have the new code.
> > What's the output of "show wal_sync_method"?
>
> "open_datasync"
This setting is only safe if you disable write cache.
> > Finally, go into device manager, find your disk, get
> properties, look
> > under Policies, is the box for "Enable write caching on the disk"
> > checked?
>
> It is checked.
>
> Does Postgres require this to be unchecked ? It is difficult
> to force customers to change it.
No, doesn't erquire it. There are a couple of different scenarios:
1) Box is checked. wal_sync_method=open_datasync. This may cause data
loss!
2) Box is checked. wal_sync_method=fsync_writethrough. This is safe.
3) Box is unchecked. wal_sync_method=open_datasync. This is safe.
4) Box is unchecked. wal_sync_method=fsync_writethrough. This is safe.
In general I would say that 1 is of course the fastest, but it's not
safe. 3 should normally be the fastest if the data is on a disk that's
only used by postgresql. 2 is probably faster if you have other
applications that also write data to the same disk. 4 is probably
*never* fastest :-)
This all assumes you don't have a battery backed cache. If you have a
controller with battery backed cache, 1 should still be the fastest, but
now it's suddenly safe.
(The basics of these changes are documented in the release notes at
http://www.postgresql.org/docs/8.0/static/release-8-0-2.html)
//Magnus
