On Mon, Jun 18, 2007 at 08:54:46PM +0200, Markus Schiltknecht wrote:
> Postgres-R has been the name of the research project by Bettina Kemme et
> al. Slony-II was the name Neil and Gavin gave their attempt to continue
> that project.
This isn't quite true. Slony-II was originally conceived by Jan as
an attempt to implement some of the Postgres-R ideas. For our uses,
however, Postgres-R had built into it a rather knotty design problem:
under high-contention workloads, it will automatically increase the
number of ROLLBACKs users experience. Jan had some ideas on how to
solve this by moving around the GC events and doing slightly
different things with them.
To that end, Afilias sponsored a small workshop in Toronto during one
of the coldest weeks the city has ever seen. This should have been a
clue, perhaps. ;-) Anyway, the upshot of this was that two or three
different approaches were attempted in prototypes. AFAIK, Neil and
Gavin got the farthest, but just about everyone who was involved in
the original workshop all independently concluded that the approach
we were attempting to get to work was doomed -- it might go, but
the overhead was great enough that it wouldn't be any benefit.
Part of the problem, as near as I could tell, was that we had no
group communication protocol that would really work. Spread needed a
_lot_ of work (where "lot of work" may mean "rewrite"), and I just
didn't have the humans to put on that problem. Another part of the
problem was that, for high-contention workloads like the ones we
happened to be working on, an optimistic approach like Postgres-R is
probably always going to be a loser.
A
--
Andrew Sullivan | ajs@crankycanuck.ca
In the future this spectacle of the middle classes shocking the avant-
garde will probably become the textbook definition of Postmodernism.
--Brad Holland
