Looking for Help on Understanding Dex Aggregators

Hi, there. I'm learning about dex aggregators. Unfortunately, I couldn't find good resources to clear my doubts. So here I am, pouring all my questions.

How often does the backend need to update its values(distances)? Does it happens on a loop, or is there an interrupt to check if a transaction on a pool occurred, and then distances are updated?

if you've any good Github/medium resources please share.