What resources can i use to better understand the architecture of a cryptocurrency exchange?

My intention is not to recreate Binance and get rich. I am learning microservices in Java and thought that developing a very basic exchange would be a great exercise and i could actually show it in my portfolio. I don't have a very good understanding of the exchange architecture. Specifically, how are the transaction implemented? If they are on-chain, then it is an asset exchange between wallets, but it cannot be accomplished in real time. So the pair trading must be off-chain to achieve real time trading. But then all assets are pooled into a special system controller wallet? In summary, how does a crypto exchange achieve real time pair trading without transaction confirmation delay?