I can't speak for other sites, but for example
https://www.moneypot.com/ is currently monitoring a few million addresses. The approach is rather simple. In my case, I pre-generated all the addresses (using bip32, but it's irrelevant). Next, I store all those addresses in a hashmap, which effectively allow constant time lookup by address.
Next, I listen on the bitcoin network and the blockchain -- when ever I see a new transaction -- I look at all the outputs and see if it corresponds to one of the them in the hashmap to see if it's in there. If it is, it records the details in a database that has an index on the address column. Actually, using an approach like this would easily allow me to monitor *every* address in the blockchain. Really, the only slow part of my scheme was just generating the initial address set
Hey, thanks for that info, how would someone come across something similar without having to spend an crap ton of time coding something like that. You solution seems logical and practical. But time for software development is not something i really have, nor funds to do something of that nature as i am sure to have someone code something like that would be a few hundred dollars a minimum.
Really, the way you do it would be perfect in my case as i do not need to sign or send transactions or anything really other than be able to pull the balance on a bunch of addresses. I have a master list in .txt of the addresses by themselves that i need to monitor. Any ideas on quick solutions or short cuts?