Aihnss.511
net.news
utzoo!decvax!ucbvax!mhtsa!ihnss!warren
Fri Dec 4 15:16:19 1981
Centralized versus distributed indices
One aspect of centralized .uindex files that Duke may not have
forseen appeared when we installed "A" netnews on some of the
general use unix machines in BTL. These machines typically have
lots of registered users (~500 entries in /etc/passwd), but few have
contact with netnews. There is also a lot of churn, as people are
moved from one machine to another to balance the load.
In this environment, rnews started to run for very long periods of
time. Most of that time seemed to be spent in making .uindex
correspond with /etc/passwd, and then going back and recoputing the
bitmap. Since this is a (# of users) X (# of articles) sort of
problem, it takes forever with 500 users and any significant number
of articles! The "B" version doesn't suffer from this, because of
its distributed index scheme. This strikes me as vastly preferable,
because it distributes the time spent doing the newscheck rather
than focussing it on the Daemon news receiving process, and it is
much more robust. (The A version was always loosing index files due
to locking problems, primarily because of the length of time it took
rnews to run).
A simple fix to our problem with the A version was to remove the
code that put users in /etc/passwd that were not in .uindex
into .uindex. This cut the run-time considerably, as the number of
users was now 5-10 as compared with 500!. The only adverse effect
is that you must actively subscribe in order to have the system keep
track of news for you. I don't think that this is a real problem,
as most people want much more than the default subscription list.
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Bruce Jones, Henry Spencer, David Wiseman.
