David Gould wrote:
>
> 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.
> 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.
Phase tree is my terminology. In my previous post I failed to mention a much
bigger reason why phase tree is not shadow paging: phase tree does not use a
shadow page table. Instead, it uses a tree where the differences between one
commit phase and the next generate a minimal set of new nodes, and only these
need to be written to disk.
-- Daniel- 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/
This archive was generated by hypermail 2b29 : Mon Jul 31 2000 - 21:00:30 EST