On Fri, Sep 01, 2023 at 01:56:18PM +0000, Andrew Poelstra via bitcoin-dev wrote: > We can swag what the space savings would be: there are 122MM utxos right > now, which is a bit under 2^27. So assuming a uniform distribution of > prefixes we'd need to specify 28 bits to identify a UTXO. To contrast, > to identify a blockheight we need 20 bits and then maybe 12 more bits to > specify a TXO within a block. Plus whatever varint overhead we have. > (I've been working on this project but busy with family stuff and don't > remember exactly where we landed on the varints for this. I think we > agreed that there was room for improvement but didn't want to hold up > posting the rest of the concept because of it.)
Since most transactions spend txouts that are similar in height to each other, you could save further bits by specifying a reference height and then encoding the exact txout with a delta. If you're sending multiple txins or multiple transactions in a single packet, you could achieve this by starting the packet with the reference block height. If your application tends to send just a single transaction, you could use a reference height that is a function of the current time. Since sender and receiver might not agree on the exact time, you could try slightly difference reference heights via bruteforcing until the transaction signatures validate. -- https://petertodd.org 'peter'[:-1]@petertodd.org
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