Re: Apache - DBI - Postgresql: Cancelling queries

If it's double-click stuff why don't you just not submit duplicate queries?
There are very many methods - e.g. must have valid token to submit query,
token only valid for one query. That sort of thing.
e.g. store hash of certain values (hidden params, sessionid) in the form
(including a random salt, and row num) in a table, as a token. Then send
the form with token to the user. When user submits form, do a select for
update on the table for that row, if particular row does not have matching
token, flag an error. If no row - flag error. Update row to invalidate the
token.

You could even limit the number of concurrent queries that way, with a bit
more overhead. You'll have a bottleneck, but since it's only for expensive
(slow) queries it might not be a big problem.

Javascript is annoying, plus if it's off it doesn't work.

Regards,
Link.

At 01:19 PM 8/1/2003 +0000, Ian Harding wrote:

>The "solution" I finally implemented seems to be pretty good, graying out
>the button after it's pushed with javascript. That means no more
>doubleclick problem, and no more hammering away at the same button. It
>does not preclude the reloading of the page (reactivating the button) or
>just going somewhere else and issuing another query.
>
>The "real" solutions involving cute little client side applets that phone
>home to the server to see if the query is still running and show a phony
>status bar seem like too much work and still don't prevent malicious
>wankers from issuing multiple queries.
>
>Good luck!
>
>Mat wrote:
>
>>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!
>>
>>
>>
>>
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