how to make website print receipt automatically?

I made a delivery website and published on my server. I have my local printer ready, there is a web page in my website which using Ajax to find all placed orders and display on webpage in every 3 seconds. I am wondering could I also connect my local printer to print out all those placed orders at same time as I display them on the page? Another question is the performance issue if I use Ajax to query placed order in every 3 seconds. for example, one day if I customise my website and make it work for more than one restaurant, Ajax query database might cause my server crash I guess.
Please help me with those two questions. 1, automatic printing order on local printer when website deployed remotely. 2, Is there other better solution to query database with nonstop and always getting realtime data without performance issue on server. For example, one new order come in, my website should display it on webpage and print it out on my local printer.

Please give me some suggestions guys, thank you.

via Chebli Mohamed