Re: O_DIRECT for WAL writes

On Mon, 2005-05-30 at 02:52 -0400, Tom Lane wrote:
> Some googling suggests so, eg
> http://www.die.net/doc/linux/man/man2/open.2.html

Well, that claims that "data is guaranteed to have been transferred",
but transferred to *where* is the question :) Transferring data to the
disk's buffers and then not asking for the buffer to be flushed is not
sufficient, for example. IMHO the fact that InnoDB uses both O_DIRECT
and fsync() is more convincing. I'm still looking for a definitive
answer, though.

The other question is whether these semantics are identical among the
various O_DIRECT implementations (e.g. Linux, FreeBSD, AIX, IRIX, and
others).

-Neil