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fees: Update MIN_CHANGE and document why

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Updates MIN_CHANGE to always allow for a subsequent bump from the
change output using RBF or CPFP of at least 2x the recommended
minumum fee, on top of the dust limit, because the previous value
did not allow enough change for performing a CPFP bump, and only
allowed for a single bumfee call, which would spend the entire
change output rather than allowing for optimization.
This commit is contained in:
Patrick Lodder 2021-09-26 20:45:36 +02:00
parent dcc22f1696
commit 16764d6e80
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GPG key ID: 2D3A345B98D0DC1F
2 changed files with 37 additions and 3 deletions
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2
qa/rpc-tests/bumpfee.py
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@ -279,7 +279,7 @@ def test_locked_wallet_fails(rbf_node, dest_address):
def test_dogecoin_wallet_minchange(rbf_node, dest_address):
input = Decimal("10.00000000")
min_change = Decimal("0.01000000")
min_change = Decimal("0.03000000")
min_fee = Decimal("0.01000000")
bumpfee = Decimal("0.001")
est_tx_size = Decimal("0.193")

38
src/wallet/wallet.h
View file

@ -66,10 +66,44 @@ static const CAmount DEFAULT_TRANSACTION_MINFEE = RECOMMENDED_MIN_TX_FEE;
* This way, replacements for fee bumps are transient rather than persisted.
*/
static const CAmount WALLET_INCREMENTAL_RELAY_FEE = RECOMMENDED_MIN_TX_FEE / 10;
/*
* Dogecoin: Creating change outputs at exactly the dustlimit is counter-
* productive because it leaves no space to bump the fee up, so we make the
* MIN_CHANGE parameter higher than the MIN_FINAL_CHANGE parameter.
*
* When RBF is not a default policy, we need to scale for both that and CPFP,
* to have a facility for those that did not manually enable RBF, yet need to
* bump a fee for their transaction to get mined.
*
* Using bumpfee currently will add WALLET_INCREMENTAL_RELAY_FEE as a fixed
* increment, and CPFP would need the spending fee for at least 147 bytes
* (1 input, 1 output), and additional space for actually increasing the fee
* for both transactions.
*
* Because the change calculation is currently not taking into account feerate
* or transaction size, we assume that most transactions are < 1kb, leading
* to the following when planning for a replacements with 2x original fee:
*
* RBF: MIN_CHANGE = dust limit + min fee or
* CPFP: MIN_CHANGE = dust limit + 2 * min fee * 0.147 + min fee
*
* Where the CPFP requirement is higher than the RBF one to lead to the same
* result.
*
* This can be rounded up to the nearest multiple of RECOMMENDED_MIN_TX_FEE as:
*
* MIN_CHANGE = DEFAULT_DUST_LIMIT + 2 * RECOMMENDED_MIN_TX_FEE
*
* The MIN_FINAL_CHANGE parameter can stay equal to DEFAULT_DUST_LIMIT as this
* influences when the wallet will discard all remaining dust as fee instead of
* change.
*/
//! target minimum change amount
static const CAmount MIN_CHANGE = RECOMMENDED_MIN_TX_FEE;
static const CAmount MIN_CHANGE = DEFAULT_DUST_LIMIT + 2 * RECOMMENDED_MIN_TX_FEE;
//! final minimum change amount after paying for fees
static const CAmount MIN_FINAL_CHANGE = RECOMMENDED_MIN_TX_FEE;
static const CAmount MIN_FINAL_CHANGE = DEFAULT_DUST_LIMIT;
//! Default for -spendzeroconfchange
static const bool DEFAULT_SPEND_ZEROCONF_CHANGE = true;
//! Default for -sendfreetransactions