Re: We really ought to do something about O_DIRECT and data=journalled on ext4

On Tue, Dec 7, 2010 at 03:34, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> To my mind, O_DIRECT is not really the key issue here, it's whether to
> prefer O_DSYNC or fdatasync.

Since different platforms implement these primitives differently, and
it's not always clear from the header file definitions which options
are actually implemented, how about simply hard-coding a default value
for each platform?

1. This would be quite straightforward to code and document (a table
of platforms and their default wal_sync_method setting)

2. The best performing (or safest) method can be chosen on every
platform. From the above discussion it seems that Windows and OSX
should default to fdatasync_writethrough even if other methods are
available

3. It would pre-empt similar surprises if other platforms change their
header files, like what happened on Linux now.

Sounds like the simple and foolproof solution.

Regards,
Marti