How to not repeat a database call everytime an ajax request is made in PHP codeignite

i am new to codeigniter and ajax requests are consuming db calls each time they are made, a simple autocomplete box will query db everytime a letter is entered and i want to be able to save results in php and not javascript after first query for later use until user leaves the page.

as an example i did a simple autocomplete input box using ajax and php(codeigniter) and it works fine, but what is the best way to do it in codeigniter? session variables or constants.php or is there a better way thank you!