[policy] lower default minrelaytxfee and incrementalrelayfee to 100sat/kvB

Let's say an attacker wants to use/exhaust the network's bandwidth, and
has the choice between renting resources from a commercial provider and
getting the network to "spam" itself it by sending unconfirmed
transactions. We'd like the latter to be more expensive than the former.

The bandwidth for relaying a transaction across the network is roughly
its serialized size (plus relay overhead) x number of nodes. A 1000vB
transaction is 1000-4000B serialized. With 100k nodes, that's 0.1-0.4GB
If the going rate for commercial services is 10c/GB, that's like 1-4c per kvB
of transaction data, so a 1000vB transaction should pay at least $0.04.

At a price of 120k USD/BTC, 100sat is about $0.12. This price allows us
to tolerate a large decrease in the conversion rate or increase in the
number of nodes.

Author: glozow

src/policy/policy.h

@@ -41,7 +41,7 @@ static constexpr unsigned int MAX_STANDARD_TX_SIGOPS_COST{MAX_BLOCK_SIGOPS_COST/
 /** The maximum number of potentially executed legacy signature operations in a single standard tx */
 static constexpr unsigned int MAX_TX_LEGACY_SIGOPS{2'500};
 /** Default for -incrementalrelayfee, which sets the minimum feerate increase for mempool limiting or replacement **/
-static constexpr unsigned int DEFAULT_INCREMENTAL_RELAY_FEE{1000};
+static constexpr unsigned int DEFAULT_INCREMENTAL_RELAY_FEE{100};
 /** Default for -bytespersigop */
 static constexpr unsigned int DEFAULT_BYTES_PER_SIGOP{20};
 /** Default for -permitbaremultisig */
@@ -63,7 +63,7 @@ static constexpr unsigned int MAX_STANDARD_SCRIPTSIG_SIZE{1650};
  * outputs below the new threshold */
 static constexpr unsigned int DUST_RELAY_TX_FEE{3000};
 /** Default for -minrelaytxfee, minimum relay fee for transactions */
-static constexpr unsigned int DEFAULT_MIN_RELAY_TX_FEE{1000};
+static constexpr unsigned int DEFAULT_MIN_RELAY_TX_FEE{100};
 /** Default for -limitancestorcount, max number of in-mempool ancestors */
 static constexpr unsigned int DEFAULT_ANCESTOR_LIMIT{25};
 /** Default for -limitancestorsize, maximum kilobytes of tx + all in-mempool ancestors */

src/test/mempool_tests.cpp

@@ -443,15 +443,15 @@ BOOST_AUTO_TEST_CASE(MempoolSizeLimitTest)
     tx1.vout.resize(1);
     tx1.vout[0].scriptPubKey = CScript() << OP_1 << OP_EQUAL;
     tx1.vout[0].nValue = 10 * COIN;
-    AddToMempool(pool, entry.Fee(10000LL).FromTx(tx1));
+    AddToMempool(pool, entry.Fee(1000LL).FromTx(tx1));
 
     CMutableTransaction tx2 = CMutableTransaction();
     tx2.vin.resize(1);
     tx2.vin[0].scriptSig = CScript() << OP_2;
     tx2.vout.resize(1);
     tx2.vout[0].scriptPubKey = CScript() << OP_2 << OP_EQUAL;
     tx2.vout[0].nValue = 10 * COIN;
-    AddToMempool(pool, entry.Fee(5000LL).FromTx(tx2));
+    AddToMempool(pool, entry.Fee(500LL).FromTx(tx2));
 
     pool.TrimToSize(pool.DynamicMemoryUsage()); // should do nothing
     BOOST_CHECK(pool.exists(tx1.GetHash()));
@@ -469,7 +469,7 @@ BOOST_AUTO_TEST_CASE(MempoolSizeLimitTest)
     tx3.vout.resize(1);
     tx3.vout[0].scriptPubKey = CScript() << OP_3 << OP_EQUAL;
     tx3.vout[0].nValue = 10 * COIN;
-    AddToMempool(pool, entry.Fee(20000LL).FromTx(tx3));
+    AddToMempool(pool, entry.Fee(2000LL).FromTx(tx3));
 
     pool.TrimToSize(pool.DynamicMemoryUsage() * 3 / 4); // tx3 should pay for tx2 (CPFP)
     BOOST_CHECK(!pool.exists(tx1.GetHash()));
@@ -481,7 +481,7 @@ BOOST_AUTO_TEST_CASE(MempoolSizeLimitTest)
     BOOST_CHECK(!pool.exists(tx2.GetHash()));
     BOOST_CHECK(!pool.exists(tx3.GetHash()));
 
-    CFeeRate maxFeeRateRemoved(25000, GetVirtualTransactionSize(CTransaction(tx3)) + GetVirtualTransactionSize(CTransaction(tx2)));
+    CFeeRate maxFeeRateRemoved(2500, GetVirtualTransactionSize(CTransaction(tx3)) + GetVirtualTransactionSize(CTransaction(tx2)));
     BOOST_CHECK_EQUAL(pool.GetMinFee(1).GetFeePerK(), maxFeeRateRemoved.GetFeePerK() + DEFAULT_INCREMENTAL_RELAY_FEE);
 
     CMutableTransaction tx4 = CMutableTransaction();
@@ -532,10 +532,10 @@ BOOST_AUTO_TEST_CASE(MempoolSizeLimitTest)
     tx7.vout[1].scriptPubKey = CScript() << OP_7 << OP_EQUAL;
     tx7.vout[1].nValue = 10 * COIN;
 
-    AddToMempool(pool, entry.Fee(7000LL).FromTx(tx4));
-    AddToMempool(pool, entry.Fee(1000LL).FromTx(tx5));
-    AddToMempool(pool, entry.Fee(1100LL).FromTx(tx6));
-    AddToMempool(pool, entry.Fee(9000LL).FromTx(tx7));
+    AddToMempool(pool, entry.Fee(700LL).FromTx(tx4));
+    AddToMempool(pool, entry.Fee(100LL).FromTx(tx5));
+    AddToMempool(pool, entry.Fee(110LL).FromTx(tx6));
+    AddToMempool(pool, entry.Fee(900LL).FromTx(tx7));
 
     // we only require this to remove, at max, 2 txn, because it's not clear what we're really optimizing for aside from that
     pool.TrimToSize(pool.DynamicMemoryUsage() - 1);
@@ -544,17 +544,17 @@ BOOST_AUTO_TEST_CASE(MempoolSizeLimitTest)
     BOOST_CHECK(!pool.exists(tx7.GetHash()));
 
     if (!pool.exists(tx5.GetHash()))
-        AddToMempool(pool, entry.Fee(1000LL).FromTx(tx5));
-    AddToMempool(pool, entry.Fee(9000LL).FromTx(tx7));
+        AddToMempool(pool, entry.Fee(100LL).FromTx(tx5));
+    AddToMempool(pool, entry.Fee(900LL).FromTx(tx7));
 
     pool.TrimToSize(pool.DynamicMemoryUsage() / 2); // should maximize mempool size by only removing 5/7
     BOOST_CHECK(pool.exists(tx4.GetHash()));
     BOOST_CHECK(!pool.exists(tx5.GetHash()));
     BOOST_CHECK(pool.exists(tx6.GetHash()));
     BOOST_CHECK(!pool.exists(tx7.GetHash()));
 
-    AddToMempool(pool, entry.Fee(1000LL).FromTx(tx5));
-    AddToMempool(pool, entry.Fee(9000LL).FromTx(tx7));
+    AddToMempool(pool, entry.Fee(100LL).FromTx(tx5));
+    AddToMempool(pool, entry.Fee(900LL).FromTx(tx7));
 
     std::vector<CTransactionRef> vtx;
     SetMockTime(42);

src/test/rbf_tests.cpp

@@ -238,10 +238,10 @@ BOOST_FIXTURE_TEST_CASE(rbf_helper_functions, TestChain100Setup)
     BOOST_CHECK(PaysForRBF(high_fee, high_fee - 1, 1, CFeeRate(0), unused_txid).has_value());
     BOOST_CHECK(PaysForRBF(high_fee + 1, high_fee, 1, CFeeRate(0), unused_txid).has_value());
     // Additional fees must cover the replacement's vsize at incremental relay fee
-    BOOST_CHECK(PaysForRBF(high_fee, high_fee + 1, 2, incremental_relay_feerate, unused_txid).has_value());
-    BOOST_CHECK(PaysForRBF(high_fee, high_fee + 2, 2, incremental_relay_feerate, unused_txid) == std::nullopt);
-    BOOST_CHECK(PaysForRBF(high_fee, high_fee + 2, 2, higher_relay_feerate, unused_txid).has_value());
-    BOOST_CHECK(PaysForRBF(high_fee, high_fee + 4, 2, higher_relay_feerate, unused_txid) == std::nullopt);
+    BOOST_CHECK(PaysForRBF(high_fee, high_fee + 1, 11, incremental_relay_feerate, unused_txid).has_value());
+    BOOST_CHECK(PaysForRBF(high_fee, high_fee + 1, 10, incremental_relay_feerate, unused_txid) == std::nullopt);
+    BOOST_CHECK(PaysForRBF(high_fee, high_fee + 2, 11, higher_relay_feerate, unused_txid).has_value());
+    BOOST_CHECK(PaysForRBF(high_fee, high_fee + 4, 20, higher_relay_feerate, unused_txid) == std::nullopt);
     BOOST_CHECK(PaysForRBF(low_fee, high_fee, 99999999, incremental_relay_feerate, unused_txid).has_value());
     BOOST_CHECK(PaysForRBF(low_fee, high_fee + 99999999, 99999999, incremental_relay_feerate, unused_txid) == std::nullopt);
 

test/functional/feature_rbf.py

@@ -585,7 +585,7 @@ def test_replacement_relay_fee(self):
 
         # Higher fee, higher feerate, different txid, but the replacement does not provide a relay
         # fee conforming to node's `incrementalrelayfee` policy of 1000 sat per KB.
-        assert_equal(self.nodes[0].getmempoolinfo()["incrementalrelayfee"], Decimal("0.00001"))
+        assert_equal(self.nodes[0].getmempoolinfo()["incrementalrelayfee"], Decimal("0.000001"))
         tx.vout[0].nValue -= 1
         assert_raises_rpc_error(-26, "insufficient fee", self.nodes[0].sendrawtransaction, tx.serialize().hex())
 

test/functional/mempool_ephemeral_dust.py

@@ -216,7 +216,7 @@ def test_non_truc(self):
 
         res = self.nodes[0].submitpackage([dusty_tx["hex"], sweep_tx["hex"]])
         assert_equal(res["package_msg"], "transaction failed")
-        assert_equal(res["tx-results"][dusty_tx["wtxid"]]["error"], "min relay fee not met, 0 < 147")
+        assert_equal(res["tx-results"][dusty_tx["wtxid"]]["error"], "min relay fee not met, 0 < 15")
 
         assert_equal(self.nodes[0].getrawmempool(), [])
 

test/functional/mempool_limit.py

@@ -206,7 +206,7 @@ def test_mid_package_replacement(self):
         # coin is no longer available, but the cache could still contain the tx.
         cpfp_parent = self.wallet.create_self_transfer(
             utxo_to_spend=replaced_tx["new_utxo"],
-            fee_rate=mempoolmin_feerate - Decimal('0.00001'),
+            fee_rate=mempoolmin_feerate - Decimal('0.000001'),
             confirmed_only=True)
 
         self.wallet.rescan_utxos()
@@ -312,9 +312,9 @@ def run_test(self):
         target_vsize_each = 50000
         assert_greater_than(target_vsize_each * 2 * 3, node.getmempoolinfo()["maxmempool"] - node.getmempoolinfo()["bytes"])
         # Should be a true CPFP: parent's feerate is just below mempool min feerate
-        parent_feerate = mempoolmin_feerate - Decimal("0.000001")  # 0.1 sats/vbyte below min feerate
+        parent_feerate = mempoolmin_feerate - Decimal("0.0000001")  # 0.01 sats/vbyte below min feerate
         # Parent + child is above mempool minimum feerate
-        child_feerate = (worst_feerate_btcvb * 1000) - Decimal("0.000001")  # 0.1 sats/vbyte below worst feerate
+        child_feerate = (worst_feerate_btcvb * 1000) - Decimal("0.0000001")  # 0.01 sats/vbyte below worst feerate
         # However, when eviction is triggered, these transactions should be at the bottom.
         # This assertion assumes parent and child are the same size.
         miniwallet.rescan_utxos()

test/functional/mempool_package_rbf.py

@@ -162,13 +162,13 @@ def test_package_rbf_additional_fees(self):
         self.log.info("Check replacement pays for incremental bandwidth")
         _, placeholder_txns3 = self.create_simple_package(coin)
         package_3_size = sum([tx.get_vsize() for tx in placeholder_txns3])
-        incremental_sats_required = Decimal(package_3_size) / COIN
-        incremental_sats_short = incremental_sats_required - Decimal("0.00000001")
+        incremental_sats_required = (Decimal(package_3_size * 0.1) / COIN).quantize(Decimal("0.00000001"))
+        incremental_sats_short = incremental_sats_required - Decimal("0.00000005")
         # Recreate the package with slightly higher fee once we know the size of the new package, but still short of required fee
         failure_package_hex3, failure_package_txns3 = self.create_simple_package(coin, parent_fee=DEFAULT_FEE, child_fee=DEFAULT_CHILD_FEE + incremental_sats_short)
         assert_equal(package_3_size, sum([tx.get_vsize() for tx in failure_package_txns3]))
         pkg_results3 = node.submitpackage(failure_package_hex3)
-        assert_equal(f"package RBF failed: insufficient anti-DoS fees, rejecting replacement {failure_package_txns3[1].txid_hex}, not enough additional fees to relay; {incremental_sats_short} < {incremental_sats_required}", pkg_results3["package_msg"])
+        assert_equal(f"package RBF failed: insufficient anti-DoS fees, rejecting replacement {failure_package_txns3[1].txid_hex}, not enough additional fees to relay; {incremental_sats_short:8f} < {incremental_sats_required:8f}", pkg_results3["package_msg"])
         self.assert_mempool_contents(expected=package_txns1)
 
         success_package_hex3, success_package_txns3 = self.create_simple_package(coin, parent_fee=DEFAULT_FEE, child_fee=DEFAULT_CHILD_FEE + incremental_sats_required)
@@ -562,12 +562,13 @@ def test_child_conflicts_parent_mempool_ancestor(self):
         )
 
         node.sendrawtransaction(grandparent_result["hex"])
+        minrelayfeerate = node.getnetworkinfo()["relayfee"]
 
         # Now make package of two descendants that looks
         # like a cpfp where the parent can't get in on its own
         self.ctr += 1
         parent_result = self.wallet.create_self_transfer(
-            fee_rate=Decimal('0.00001000'),
+            fee_rate=minrelayfeerate,
             utxo_to_spend=grandparent_result["new_utxo"],
             sequence=MAX_BIP125_RBF_SEQUENCE - self.ctr,
         )

test/functional/p2p_1p1c_network.py

@@ -13,9 +13,11 @@
 from math import ceil
 
 from test_framework.mempool_util import (
+    DEFAULT_MIN_RELAY_TX_FEE,
     fill_mempool,
 )
 from test_framework.messages import (
+    COIN,
     msg_tx,
 )
 from test_framework.p2p import (
@@ -31,9 +33,6 @@
     MiniWalletMode,
 )
 
-# 1sat/vB feerate denominated in BTC/KvB
-FEERATE_1SAT_VB = Decimal("0.00001000")
-
 class PackageRelayTest(BitcoinTestFramework):
     def set_test_params(self):
         self.setup_clean_chain = True
@@ -49,12 +48,12 @@ def raise_network_minfee(self):
 
         self.log.debug("Check that all nodes' mempool minimum feerates are above min relay feerate")
         for node in self.nodes:
-            assert_equal(node.getmempoolinfo()['minrelaytxfee'], FEERATE_1SAT_VB)
-            assert_greater_than(node.getmempoolinfo()['mempoolminfee'], FEERATE_1SAT_VB)
+            assert_equal(node.getmempoolinfo()['minrelaytxfee'], Decimal(DEFAULT_MIN_RELAY_TX_FEE) / COIN)
+            assert_greater_than(node.getmempoolinfo()['mempoolminfee'], Decimal(DEFAULT_MIN_RELAY_TX_FEE) / COIN)
 
     def create_basic_1p1c(self, wallet):
-        low_fee_parent = wallet.create_self_transfer(fee_rate=FEERATE_1SAT_VB, confirmed_only=True)
-        high_fee_child = wallet.create_self_transfer(utxo_to_spend=low_fee_parent["new_utxo"], fee_rate=999*FEERATE_1SAT_VB)
+        low_fee_parent = wallet.create_self_transfer(fee_rate=Decimal(DEFAULT_MIN_RELAY_TX_FEE) / COIN, confirmed_only=True)
+        high_fee_child = wallet.create_self_transfer(utxo_to_spend=low_fee_parent["new_utxo"], fee_rate=999*Decimal(DEFAULT_MIN_RELAY_TX_FEE)/ COIN)
         package_hex_basic = [low_fee_parent["hex"], high_fee_child["hex"]]
         return package_hex_basic, low_fee_parent["tx"], high_fee_child["tx"]
 
@@ -85,8 +84,8 @@ def create_package_2outs(self, wallet):
         return [low_fee_parent_2outs["hex"], high_fee_child_2outs["hex"]], low_fee_parent_2outs["tx"], high_fee_child_2outs["tx"]
 
     def create_package_2p1c(self, wallet):
-        parent1 = wallet.create_self_transfer(fee_rate=FEERATE_1SAT_VB*10, confirmed_only=True)
-        parent2 = wallet.create_self_transfer(fee_rate=FEERATE_1SAT_VB*20, confirmed_only=True)
+        parent1 = wallet.create_self_transfer(fee_rate=Decimal(DEFAULT_MIN_RELAY_TX_FEE) / COIN * 10, confirmed_only=True)
+        parent2 = wallet.create_self_transfer(fee_rate=Decimal(DEFAULT_MIN_RELAY_TX_FEE) / COIN * 20, confirmed_only=True)
         child = wallet.create_self_transfer_multi(
             utxos_to_spend=[parent1["new_utxo"], parent2["new_utxo"]],
             fee_per_output=999*parent1["tx"].get_vsize(),

test/functional/p2p_ibd_txrelay.py

@@ -28,17 +28,17 @@
 )
 from test_framework.test_framework import BitcoinTestFramework
 
-MAX_FEE_FILTER = Decimal(9170997) / COIN
-NORMAL_FEE_FILTER = Decimal(100) / COIN
+MAX_FEE_FILTER = Decimal(9936506) / COIN
+NORMAL_FEE_FILTER = Decimal(10) / COIN
 
 
 class P2PIBDTxRelayTest(BitcoinTestFramework):
     def set_test_params(self):
         self.setup_clean_chain = True
         self.num_nodes = 2
         self.extra_args = [
-            ["-minrelaytxfee={}".format(NORMAL_FEE_FILTER)],
-            ["-minrelaytxfee={}".format(NORMAL_FEE_FILTER)],
+            ["-minrelaytxfee={:.8f}".format(NORMAL_FEE_FILTER)],
+            ["-minrelaytxfee={:.8f}".format(NORMAL_FEE_FILTER)],
         ]
 
     def run_test(self):

test/functional/p2p_opportunistic_1p1c.py

@@ -13,10 +13,12 @@
 from test_framework.blocktools import MAX_STANDARD_TX_WEIGHT
 from test_framework.mempool_util import (
     create_large_orphan,
+    DEFAULT_MIN_RELAY_TX_FEE,
     fill_mempool,
 )
 from test_framework.messages import (
     CInv,
+    COIN,
     COutPoint,
     CTransaction,
     CTxIn,
@@ -79,13 +81,13 @@ def set_test_params(self):
         ]]
 
     def create_tx_below_mempoolminfee(self, wallet, utxo_to_spend=None):
-        """Create a 1-input 1sat/vB transaction using a confirmed UTXO. Decrement and use
+        """Create a 1-input 0.1sat/vB transaction using a confirmed UTXO. Decrement and use
         self.sequence so that subsequent calls to this function result in unique transactions."""
 
         self.sequence -= 1
-        assert_greater_than(self.nodes[0].getmempoolinfo()["mempoolminfee"], FEERATE_1SAT_VB)
+        assert_greater_than(self.nodes[0].getmempoolinfo()["mempoolminfee"], Decimal(DEFAULT_MIN_RELAY_TX_FEE) / COIN)
 
-        return wallet.create_self_transfer(fee_rate=FEERATE_1SAT_VB, sequence=self.sequence, utxo_to_spend=utxo_to_spend, confirmed_only=True)
+        return wallet.create_self_transfer(fee_rate=Decimal(DEFAULT_MIN_RELAY_TX_FEE) / COIN, sequence=self.sequence, utxo_to_spend=utxo_to_spend, confirmed_only=True)
 
     @cleanup
     def test_basic_child_then_parent(self):