Sweep up dust inputs when there is room #1675

The coin selection should automatically sweep up excessive small / dust inputs in order to get them out of the txout set when there is room and the txn already has change. (e.g. excess priority before the txn loses freeness, or room before the next kiliobyte fee increment)

This can be done as a post-processing step after the existing selection.

Care should be taken to avoid reducing privacy by linking otherwise independent accounts. This can sometimes increase privacy by further disguising the values exchange.

But fees might not be rounded to kilobyte (and aren't any more, with Gavin's changes, AFAIK)

Er. I'd missed that. I think we should keep the rounding behavior, both for improved compatibility with current behavior, and also because it leaves some free room for housekeeping operations like this.

Is this related? http://www.reddit.com/r/Bitcoin/comments/12h1ec/how_to_minimize_fees_by_sending_dust_inputs_to/

I would say that it is more important to structure costs correctly. It is the creation of dust txouts that causes both the expense of storing them on the blockchain and the eventual expense of redeeming them. A better solution IMO would be to make txins free and calculate fees based on txouts, and then allow clients sweep all dust from their accounts at will.

@Cryddit alas, for a miner, making them free would be economically irrational since the scarcity creating the market to begin with is the maximum size of the block.

(Also, making txins free entirely has the risk of people stuffing kilobytes of data in them for parasitic storage)

@gmaxwell This can be closed. We finally got rid of rounding up to the next 1kB in #7103 (rebase of #6708) and it's really unlikely those changes get reverted.

@MarcoFalke I suppose you can close this now that you're a member?