Apache - DBI - Postgresql: Cancelling queries

I am having trouble with users firing off a query from the web
interface, and then getting bored of waiting and firing off a different
query.

As http is stateless apache, (and so the perl cgi script) only realises
that the user has gone when it ties to send data back to the user and
gets a "broken pipe" type response. This is usually too late as by this
time the query has completed, using up valuable resources.

Is there a tried and tested solution to this problem?
If so please let me know!

If not...

I am working on a work around at the moment but have run into trouble!

I have read the DBI man pages but there doesn't seem to be a cancel
query function implemented, can anyone confirm or deny this?

Can i send some control sequence using DBI to cancel the query?

I had taken the approach of having two perl threads, one to run the
query and one to poll the browser every second to see if the user is
still there. Plan X was then to cancel the query if the user had ended
the connection.

The first problem was the lack of cancel query, second problem seems to
be that the DBI database handles cannot be shared between thread - so i
will have to pass a signal to the thread waiting for query to return to
cancel it? anyone else tried this? any more gaping pitfalls that i
should be aware of?!

Thanks!