What would it take to change the protocol?

[IveBeenBit]

This post talks about the large number of transactions added to the network by Satoshi Dice. Much of the discussion in the thread is about "pruning" or "compressing" the block chain so it doesn't take up as much space on nodes' hard drives and get unwieldy as number of transactions continues to increase.

What would it take to do that? I thought I remembered hearing that for any changes made in the protocol, unanimous adoption of the new client by all miners would be necessary. Requiring unanimous adoption seems like a good way to not ever get any changes done because all it would take is one person to not update, or gum up the works just because.

Or maybe I understand it incorrectly.

What would it take to implement a block-chain pruning solution?

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[Kazimir]

I think first of all there would have to be general acceptance by the community. Once this feature is agreed upon, it can be implemented in various clients and mining software, and set to become active from a predefined moment in the future (e.g. from a specific block number that's still to come). Once this protocol change is implemented, it should be announced in a timely manner, to make sure everybody has the opportunity to update their client before the change goes into effect.

[deepceleron]

Some of the optimization desired, cleaning the locally stored blockchain, could be done on the local client without network approval - removing zero-balance addresses from the transaction record database and blockchain index. This likely won't be put into the main Bitcoin client as history is important too (being able to look up past payments). Also, the blockchain is distributed peer-to-peer, you couldn't share blocks that have had data pruned out of them.

The blockchain database also need not be stored locally in the BerkeleyDB format used by the mainline client, it could be more highly compressed and optimized.

[realnowhereman]

Pruning doesn't require a protocol change; it requires a client change.  It'll happen in the end when the developers see it as a priority.