Re: File system performance and pg_xlog

On Sat, May 05, 2001 at 06:43:51PM -0400, mlw wrote:
> Marko Kreen wrote:
> > On Sat, May 05, 2001 at 01:09:38PM -0400, mlw wrote:
> > > A small debate started with bad performance on ReiserFS. I pondered the likely
> > > advantages to raw device access. It also occured to me that the FAT file system
> > > is about as close to a managed raw device as one could get. So I did some
> > > tests:

> I think a "pgfs" could easily be a derivative of FAT, or even FAT with some
> Ioctls.  It is simple, it is fast, it does not attempt to do things postgres
> doesn't need.

Well, my opinion too is that it is waste of resources to try
implement PostgreSQL-specific filesystem.  As you already showed
that there are noticeable differences of different filesystems,
the Right Thing would be to make a FAQ/web-page/knowledge-base
of comments on different filesystem in point of view of DB
(PostgreSQL) server.

Also users will have different priorities:
reliability/speed-of-reads/speed-of-writes - I mean different
users have them ordered differently - so it should be mentioned
this fs is good for this but bad on this, etc...  It is good
to put this part of db on this fs but not that part of db...
Suggestions on mount flags to use...

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
* a lot of code should be reimplemented that already exists in today's OS'es
* you lose all of UNIX user-space tools
* 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
ofbetter and there should be a os/fs combo that is 95% perfect.
 


-- 
marko