I had a similar problem and there a couple ways of approaching it. I opted for turning off buffering and printing a "Pleast wait" message and emitting a "." or similar every thousand or so records so they wouldn't hit refresh and spawn another copy of the process.
Then when it was finished I displayed the results.

You could also fork the actual search off as another process and display a "searching.." page with a meta-refresh or server-push, this way you could handle problems with impatient people spawning lots of processes.

You might also be interested in this related node.

-Lee

"To be civilized is to deny one's nature."