Remove -mempoolreplacement to prevent needless block prop slowness.

At this point there is no reasonable excuse to disable opt-in RBF,
and, unlike when this option was added, there are now significant
issues created when disabling it (in the form of compact block
reconstruction failures). Further, it breaks a lot of modern wallet
behavior.

doc/man/bitcoin-qt.1

@@ -488,9 +488,6 @@ Relay and mine data carrier transactions (default: 1)
 Maximum size of data in data carrier transactions we relay and mine
 (default: 83)
 .HP
-\fB\-mempoolreplacement\fR
-.IP
-Enable transaction replacement in the memory pool (default: 1)
 .HP
 \fB\-minrelaytxfee=\fR<amt>
 .IP

doc/man/bitcoind.1

@@ -488,10 +488,6 @@ Relay and mine data carrier transactions (default: 1)
 Maximum size of data in data carrier transactions we relay and mine
 (default: 83)
 .HP
-\fB\-mempoolreplacement\fR
-.IP
-Enable transaction replacement in the memory pool (default: 1)
-.HP
 \fB\-minrelaytxfee=\fR<amt>
 .IP
 Fees (in BTC/kB) smaller than this are considered zero fee for relaying,

src/init.cpp

@@ -524,7 +524,6 @@ void SetupServerArgs()
     gArgs.AddArg("-bytespersigop", strprintf("Equivalent bytes per sigop in transactions for relay and mining (default: %u)", DEFAULT_BYTES_PER_SIGOP), false, OptionsCategory::NODE_RELAY);
     gArgs.AddArg("-datacarrier", strprintf("Relay and mine data carrier transactions (default: %u)", DEFAULT_ACCEPT_DATACARRIER), false, OptionsCategory::NODE_RELAY);
     gArgs.AddArg("-datacarriersize", strprintf("Maximum size of data in data carrier transactions we relay and mine (default: %u)", MAX_OP_RETURN_RELAY), false, OptionsCategory::NODE_RELAY);
-    gArgs.AddArg("-mempoolreplacement", strprintf("Enable transaction replacement in the memory pool (default: %u)", DEFAULT_ENABLE_REPLACEMENT), false, OptionsCategory::NODE_RELAY);
     gArgs.AddArg("-minrelaytxfee=<amt>", strprintf("Fees (in %s/kB) smaller than this are considered zero fee for relaying, mining and transaction creation (default: %s)",
         CURRENCY_UNIT, FormatMoney(DEFAULT_MIN_RELAY_TX_FEE)), false, OptionsCategory::NODE_RELAY);
     gArgs.AddArg("-whitelistforcerelay", strprintf("Force relay of transactions from whitelisted peers even if the transactions were already in the mempool or violate local relay policy (default: %d)", DEFAULT_WHITELISTFORCERELAY), false, OptionsCategory::NODE_RELAY);
@@ -1176,15 +1175,6 @@ bool AppInitParameterInteraction()
 
     nMaxTipAge = gArgs.GetArg("-maxtipage", DEFAULT_MAX_TIP_AGE);
 
-    fEnableReplacement = gArgs.GetBoolArg("-mempoolreplacement", DEFAULT_ENABLE_REPLACEMENT);
-    if ((!fEnableReplacement) && gArgs.IsArgSet("-mempoolreplacement")) {
-        // Minimal effort at forwards compatibility
-        std::string strReplacementModeList = gArgs.GetArg("-mempoolreplacement", "");  // default is impossible
-        std::vector<std::string> vstrReplacementModes;
-        boost::split(vstrReplacementModes, strReplacementModeList, boost::is_any_of(","));
-        fEnableReplacement = (std::find(vstrReplacementModes.begin(), vstrReplacementModes.end(), "fee") != vstrReplacementModes.end());
-    }
-
     return true;
 }
 

src/validation.cpp

@@ -111,7 +111,6 @@ bool fCheckpointsEnabled = DEFAULT_CHECKPOINTS_ENABLED;
 size_t nCoinCacheUsage = 5000 * 300;
 uint64_t nPruneTarget = 0;
 int64_t nMaxTipAge = DEFAULT_MAX_TIP_AGE;
-bool fEnableReplacement = DEFAULT_ENABLE_REPLACEMENT;
 
 uint256 hashAssumeValid;
 arith_uint256 nMinimumChainWork;
@@ -486,15 +485,12 @@ static bool AcceptToMemoryPoolWorker(const CChainParams& chainparams, CTxMemPool
                 // unconfirmed ancestors anyway; doing otherwise is hopelessly
                 // insecure.
                 bool fReplacementOptOut = true;
-                if (fEnableReplacement)
+                for (const CTxIn &_txin : ptxConflicting->vin)
                 {
-                    for (const CTxIn &_txin : ptxConflicting->vin)
+                    if (_txin.nSequence <= MAX_BIP125_RBF_SEQUENCE)
                     {
-                        if (_txin.nSequence <= MAX_BIP125_RBF_SEQUENCE)
-                        {
-                            fReplacementOptOut = false;
-                            break;
-                        }
+                        fReplacementOptOut = false;
+                        break;
                     }
                 }
                 if (fReplacementOptOut) {

src/validation.h

@@ -116,8 +116,6 @@ static const char* const DEFAULT_BLOCKFILTERINDEX = "0";
 static const unsigned int DEFAULT_BANSCORE_THRESHOLD = 100;
 /** Default for -persistmempool */
 static const bool DEFAULT_PERSIST_MEMPOOL = true;
-/** Default for -mempoolreplacement */
-static const bool DEFAULT_ENABLE_REPLACEMENT = true;
 /** Default for using fee filter */
 static const bool DEFAULT_FEEFILTER = true;
 
@@ -160,7 +158,6 @@ extern size_t nCoinCacheUsage;
 extern CFeeRate minRelayTxFee;
 /** If the tip is older than this (in seconds), the node is considered to be in initial block download. */
 extern int64_t nMaxTipAge;
-extern bool fEnableReplacement;
 
 /** Block hash whose ancestors we will assume to have valid scripts without checking them. */
 extern uint256 hashAssumeValid;

test/functional/feature_rbf.py

@@ -64,7 +64,7 @@ def make_utxo(node, amount, confirmed=True, scriptPubKey=CScript([1])):
 
 class ReplaceByFeeTest(BitcoinTestFramework):
     def set_test_params(self):
-        self.num_nodes = 2
+        self.num_nodes = 1
         self.extra_args = [
             [
                 "-maxorphantx=1000",
@@ -74,9 +74,6 @@ class ReplaceByFeeTest(BitcoinTestFramework):
                 "-limitdescendantcount=200",
                 "-limitdescendantsize=101",
             ],
-            [
-                "-mempoolreplacement=0",
-            ],
         ]
 
     def skip_test_if_missing_module(self):
@@ -148,16 +145,12 @@ class ReplaceByFeeTest(BitcoinTestFramework):
 
         # This will raise an exception due to insufficient fee
         assert_raises_rpc_error(-26, "insufficient fee", self.nodes[0].sendrawtransaction, tx1b_hex, 0)
-        # This will raise an exception due to transaction replacement being disabled
-        assert_raises_rpc_error(-26, "txn-mempool-conflict", self.nodes[1].sendrawtransaction, tx1b_hex, 0)
 
         # Extra 0.1 BTC fee
         tx1b = CTransaction()
         tx1b.vin = [CTxIn(tx0_outpoint, nSequence=0)]
         tx1b.vout = [CTxOut(int(0.9 * COIN), CScript([b'b' * 35]))]
         tx1b_hex = txToHex(tx1b)
-        # Replacement still disabled even with "enough fee"
-        assert_raises_rpc_error(-26, "txn-mempool-conflict", self.nodes[1].sendrawtransaction, tx1b_hex, 0)
         # Works when enabled
         tx1b_txid = self.nodes[0].sendrawtransaction(tx1b_hex, 0)
 
@@ -168,11 +161,6 @@ class ReplaceByFeeTest(BitcoinTestFramework):
 
         assert_equal(tx1b_hex, self.nodes[0].getrawtransaction(tx1b_txid))
 
-        # Second node is running mempoolreplacement=0, will not replace originally-seen txn
-        mempool = self.nodes[1].getrawmempool()
-        assert tx1a_txid in mempool
-        assert tx1b_txid not in mempool
-
     def test_doublespend_chain(self):
         """Doublespend of a long chain"""