Utilizing "direct writes" Re: File system performance and pg_xlog

* Marko Kreen <marko@l-t.ee> [010505 17:39] wrote:
> 
> There already exist bazillion filesystems, _some_ of them should
> be usable for PostgreSQL too :)
> 
> Besides resource waste there are others problems with app-level
> fs:
> 
> * double-buffering and incompatibilities of avoiding that

Depends on the OS, most Operating systems like FreeBSD and Solaris
offer character device access, this means that the OS will DMA
directly from the process's address space.  Avoiding the double
copy is trivial except that one must align and size writes correctly,
generally on 512 byte boundries and in 512 byte increments.

> * a lot of code should be reimplemented that already exists
>   in today's OS'es

That's true.

> * you lose all of UNIX user-space tools

Even worse. :)

> * the speed difference will not be very big.  Remeber: it _was_
>   big on OS'es and fs' in year 1990.  Today's fs are lot of
>   better and there should be a os/fs combo that is 95% perfect.

Well, here's an idea, has anyone tried using the "direct write"
interface that some OS's offer?  I doubt FreeBSD does, but I'm
positive that Solaris offers it as well as possibly IRIX.

-- 
-Alfred Perlstein - [alfred@freebsd.org]
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