Doesn't anyone know if new transactions are added to the list at random places.
Or are they always added on top.
Transactions aren't reordered within a single wallet, and new transactions are always added to the top, though transactions could be reordered if you move keys between wallets or use -zapwallettxes.
I want to have a scalable way of getting all the new "receive" transactions.
listtransactions loops through every transaction in your wallet, so it isn't very fast or scalable. It's better to use one of these:
- getreceivedbyaccount or getreceivedbyaddress
- -walletnotify + gettransaction
- listsinceblock
Keep in mind that the chain can reorg, which can cause confirmed transactions to have a different number of confirmations or even become invalid. You need to handle this, especially if you use walletnotify or listsinceblock. I know that they're limited and a bit confusing, but I usually recommend bitcoind accounts for small- to medium-size sites because it's very easy to do things correctly with them.