see this fiddle
http://jsfiddle.net/nx7g756d/If you write something fast example "12 34 56 78"
then there will be more than 3 request to the server

it will eat huge memory on server PC.

or
can i just cancel all AJAX request that combobox made except the last one?
see this autocomplete plugin
https://github.com/devbridge/jQuery-Autocompletethe plugin above they have smart system that
cancell all request made before the last one so the server not be flooded by request

Thank you in advance