[Bitcoin-development] Proposed alternatives to the 20MB step function

Tier Nolan tier.nolan at gmail.com
Sat May 9 13:49:53 UTC 2015

On Sat, May 9, 2015 at 12:58 PM, Gavin Andresen <gavinandresen at gmail.com>

> RE: fixing sigop counting, and building in UTXO cost: great idea! One of
> the problems with this debate is it is easy for great ideas get lost in all
> the noise.

If the UTXO set cost is built in, UTXO database entries suddenly are worth
something, in addition to the bitcoin held in that entry.

A user's client might display how many they own.  When sending money to a
merchant, the user might demand the merchant indicate a slot to pay to.

The user could send an ANYONE_CAN_PAY partial transaction.  The transaction
would guarantee that the user has at least as many UTXOs as before.

Discussing the possibility of doing this creates an incentive to bloat the
UTXO set right now, since UTXOs would be valuable in the future.

The objective would be to make them valuable enough to encourage
conservation, but not so valuable that the UTXO contains more value than
the bitcoins in the output.

Gmaxwell's suggested "tx_size = MAX( real_size >> 1,  real_size +
4*utxo_created_size - 3*utxo_consumed_size)" for a 250 byte transaction
with 1 input and 2 outputs has very little effect.

real_size + 4 * (2) - 3 * 1 = 255

That gives a 2% size penalty for adding an extra UTXO.  I doubt that is
enough to change behavior.

The UTXO set growth could be limited directly.  A block would be invalid if
it increases the number of UTXO entries above the charted path.

RE: a hard upper limit, with a dynamic limit under it:

If the block is greater than 32MB, then it means an update to how blocks
are broadcast, so that could be a reasonable hard upper limit (or maybe
31MB, or just the 20MB already suggested).
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