Re: Document how to turn off disk write cache on popular operating

Magnus Hagander wrote:
> > > Should this mention that you don't need to turn it off at the disk level if
> > > you use fsync_writethrough? 
> > 
> > Uh, I remember we looked at this checkbox before but I don't remember
> > the details, and I can't find a comment about it.  Was the issue that
> > writethrough always forces through the disk cache?  Is that the default
> > on Win32?  Did we comment this somewhere?
> 
> If you set it to fsync or fsync_writethrough it will write through the
> cache. (fsync is just an alias)
> If you set it to OPEN_DATASYNC, it will respond to the checkbox you are
> referring to.
> 
> OPEN_DATASYNC is the default, IIRC.

OK, docs updated:
  On <productname>Windows</> if <varname>wal_sync_method</> is  <literal>open_datasync</> (the default), write caching
isdisabled by  unchecking <literal>My Computer\Open\{select disk  drive}\Properties\Hardware\Properties\Policies\Enable
writecaching on  the disk</>.  Also on Windows, <literal>fsync</> and  <literal>fsync_writethrough</> never do write
caching.

--  Bruce Momjian  <bruce@momjian.us>        http://momjian.us EnterpriseDB
http://postgres.enterprisedb.com
 + If your life is a hard drive, Christ can be your backup. +