On Tue, Jul 25, 2000 at 12:16:42PM +0200, Daniel Phillips wrote:
> Please excuse me for the delay in responding to this...
Me too...
> "Stephen C. Tweedie" wrote:
> >
> > On Thu, Jul 06, 2000 at 09:19:58PM +0100, Steve Whitehouse wrote:
> > > can you explain "phase tree" and/or give a reference ?
> >
> > For a reference, wait until ALS and see the ext2-derived filesystem
> > report. :-)
>
> Which is when I'll deliver my white paper on Tux2fs - thanks for
> being mysterious and building up the anticpation. ;-)
>
> > For basic background, look up some of the WAFL white papers from
> > NetApps. The basic idea is an old database one: you have your
> > filesystem in a tree, and whenever you modify the tree, you write into
> > new blocks. Then the next level up in the tree --- which contains
> > pointers to the old blocks --- gets modified to point to the new
> > blocks, and those changes too get written to new blocks, so you then
> > need to update the pointers in the _next_ level up the tree.
> >
> > So you do your changes right up the tree, allocating all your new
> > blocks in sequential order on disk somewhere (anywhere, unlike a LFS),
> > and now all you need to do to make the entire new set of writes
> > visible after a reboot is to move the root node pointer for the
> > filesystem from the old root block to the new one. It's a beautiful
> > mechanism for achieving transactional consistency, and it lends itself
I had not heard the term "phase tree", but from your description is sounds
exactly like what is often called "shadow paging". Which may make sense for
file systems, but none of the commercial DB engines use it, probably because
of the latency issues you mention.
Or have I misunderstood?
-dg
-- David Gould dg@suse.com SuSE, Inc., 580 2cd St. #210, Oakland, CA 94607 510.628.3380 "I sense a disturbance in the source" -- Alan Cox- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.rutgers.edu Please read the FAQ at http://www.tux.org/lkml/
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