But, um, backing to Steve's original scenario:
For your case of "firing off the same slow query again and again
bringing the server to its knees", if there's a legitimate reason for
that query to be slow (it really is doing hard important work, it's
not just written poorly), then what you want to do is prevent the
firing off of the queries 2 to N, not abort each N-1 query query as
query N is submitted.
Probably that means you need some UI to let the user go find the
results of the query he submitted earlier, as he will have clicked
away to another page in the meantime. In OpenACS, a simple smallish
scale system for that shouldn't be too hard to do. You already have
every logged in user uniquely identified, so only allow each user to
run query Q once ever N minutes, and cache the results of the query in
a NSV for N or N*2 minutes as well, or something like that.
Of course, that's assuming that the expensive query is giving
different results for each user. If all your users are
running the same query with the same results, then none of that fancy
stuff is necessary, all you need is a little cacheing in AOLserver and
you're done. You're users will never see any difference except in
speed. And you originally said this is for an E-commerce site...
Most of the time query tuning and maybe some cacheing is probably all
they need.
