46. On Scalability and Lightweight Clients

46

On Scalability and Lightweight Clients

AS TIME PASSES, the block chain, which contains a record of all transactions made since January 2009, grows continuously. Given a Bitcoin wallet containing several Bitcoin addresses along with their corresponding private keys and bitcoin balances, Bitcoin must know which address or addresses should be used to cover a transaction. For example, assume that Bitcoin address A has 0.1 BTC, B has 0.2 BTC, and C has 0.3 BTC and that a payment of 0.5 BTC is to be made. The Bitcoin wallet will have to pick a combination of 2 or more Bitcoin addresses with which to cover the 0.5 BTC as none of them individually has sufficient bitcoins to make the entire payment. Unless a Bitcoin client has the full block chain and so is able to know the current balance of each address, it must interface with a server that does have the block chain. The Simplified Payment Verification, first described in Satoshi’s original Bitcoin paper, allows clients to rely on a server participating in the Bitcoin network that has the full block chain but may or may not be participating in the mining process. It was implemented later and benefits lightweight clients.

Re: Scalability

Satoshi Nakamoto July 14, 2010, 09:10:52 PM

Quote from: jib on July 12, 2010, 11:36:17 AM

Am I correct in understanding that every node receives information about every transaction (as the technical paper says)? Doesn’t that make bitcoin completely impractical for use as a currency on a large scale?

The design outlines a lightweight client that does not need the full block chain. In the design PDF it’s called Simplified Payment Verification.

The lightweight client can send and receive transactions, it just can’t generate blocks. It does not need to trust a node to verify payments, it can still verify them itself.The lightweight client is not implemented yet, but the plan is to implement it when it’s needed. For now, everyone just runs a full network node.

I anticipate there will never be more than 100K nodes, probably less. It will reach an equilibrium where it’s not worth it for more nodes to join in. The rest will be lightweight clients, which could be millions.

At equilibrium size, many nodes will be server farms with one or two network nodes that feed the rest of the farm over a LAN.