Introduce -incrementalrelayfee

5 files changed, 24 insertions, 11 deletions

diff --git a/src/init.cpp b/src/init.cpp
index b0c045da15..f3a3a1d276 100644
--- a/src/init.cpp
+++ b/src/init.cpp
@@ -465,8 +465,10 @@ std::string HelpMessage(HelpMessageMode mode)
     AppendParamsHelpMessages(strUsage, showDebug);
 
     strUsage += HelpMessageGroup(_("Node relay options:"));
-    if (showDebug)
+    if (showDebug) {
         strUsage += HelpMessageOpt("-acceptnonstdtxn", strprintf("Relay and mine \"non-standard\" transactions (%sdefault: %u)", "testnet/regtest only; ", !Params(CBaseChainParams::TESTNET).RequireStandard()));
+        strUsage += HelpMessageOpt("-incrementalrelayfee=<amt>", strprintf("Fee rate (in %s/kB) used to define cost of relay, used for mempool limiting and BIP 125 replacement. (default: %s)", CURRENCY_UNIT, FormatMoney(DEFAULT_INCREMENTAL_RELAY_FEE)));
+    }
     strUsage += HelpMessageOpt("-bytespersigop", strprintf(_("Equivalent bytes per sigop in transactions for relay and mining (default: %u)"), DEFAULT_BYTES_PER_SIGOP));
     strUsage += HelpMessageOpt("-datacarrier", strprintf(_("Relay and mine data carrier transactions (default: %u)"), DEFAULT_ACCEPT_DATACARRIER));
     strUsage += HelpMessageOpt("-datacarriersize", strprintf(_("Maximum size of data in data carrier transactions we relay and mine (default: %u)"), MAX_OP_RETURN_RELAY));
@@ -923,6 +925,15 @@ bool AppInitParameterInteraction()
     int64_t nMempoolSizeMin = GetArg("-limitdescendantsize", DEFAULT_DESCENDANT_SIZE_LIMIT) * 1000 * 40;
     if (nMempoolSizeMax < 0 || nMempoolSizeMax < nMempoolSizeMin)
         return InitError(strprintf(_("-maxmempool must be at least %d MB"), std::ceil(nMempoolSizeMin / 1000000.0)));
+    // incremental relay fee sets the minimimum feerate increase necessary for BIP 125 replacement in the mempool
+    // and the amount the mempool min fee increases above the feerate of txs evicted due to mempool limiting.
+    if (IsArgSet("-incrementalrelayfee"))
+    {
+        CAmount n = 0;
+        if (!ParseMoney(GetArg("-incrementalrelayfee", ""), n))
+            return InitError(AmountErrMsg("incrementalrelayfee", GetArg("-incrementalrelayfee", "")));
+        incrementalRelayFee = CFeeRate(n);
+    }
 
     // -par=0 means autodetect, but nScriptCheckThreads==0 means no concurrency
     nScriptCheckThreads = GetArg("-par", DEFAULT_SCRIPTCHECK_THREADS);
@@ -969,6 +980,10 @@ bool AppInitParameterInteraction()
             return InitError(AmountErrMsg("minrelaytxfee", GetArg("-minrelaytxfee", "")));
         // High fee check is done afterward in CWallet::ParameterInteraction()
         ::minRelayTxFee = CFeeRate(n);
+    } else if (incrementalRelayFee > ::minRelayTxFee) {
+        // Allow only setting incrementalRelayFee to control both
+        ::minRelayTxFee = incrementalRelayFee;
+        LogPrintf("Increasing minrelaytxfee to %s to match incrementalrelayfee\n",::minRelayTxFee.ToString());
     }
 
     // Sanity check argument for min fee for including tx in block
diff --git a/src/policy/policy.cpp b/src/policy/policy.cpp
index d318a0997c..4dacd6b545 100644
--- a/src/policy/policy.cpp
+++ b/src/policy/policy.cpp
@@ -206,6 +206,7 @@ bool IsWitnessStandard(const CTransaction& tx, const CCoinsViewCache& mapInputs)
     return true;
 }
 
+CFeeRate incrementalRelayFee = CFeeRate(DEFAULT_INCREMENTAL_RELAY_FEE);
 unsigned int nBytesPerSigOp = DEFAULT_BYTES_PER_SIGOP;
 
 int64_t GetVirtualTransactionSize(int64_t nWeight, int64_t nSigOpCost)
diff --git a/src/policy/policy.h b/src/policy/policy.h
index 5c6a7b1865..039122a59e 100644
--- a/src/policy/policy.h
+++ b/src/policy/policy.h
@@ -30,6 +30,8 @@ static const unsigned int MAX_P2SH_SIGOPS = 15;
 static const unsigned int MAX_STANDARD_TX_SIGOPS_COST = MAX_BLOCK_SIGOPS_COST/5;
 /** Default for -maxmempool, maximum megabytes of mempool memory usage */
 static const unsigned int DEFAULT_MAX_MEMPOOL_SIZE = 300;
+/** Default for -incrementalrelayfee, which sets the minimum feerate increase for mempool limiting or BIP 125 replacement **/
+static const unsigned int DEFAULT_INCREMENTAL_RELAY_FEE = 1000;
 /** Default for -bytespersigop */
 static const unsigned int DEFAULT_BYTES_PER_SIGOP = 20;
 /** The maximum number of witness stack items in a standard P2WSH script */
@@ -85,6 +87,7 @@ bool AreInputsStandard(const CTransaction& tx, const CCoinsViewCache& mapInputs)
      */
 bool IsWitnessStandard(const CTransaction& tx, const CCoinsViewCache& mapInputs);
 
+extern CFeeRate incrementalRelayFee;
 extern unsigned int nBytesPerSigOp;
 
 /** Compute the virtual transaction size (weight reinterpreted as bytes). */
diff --git a/src/txmempool.cpp b/src/txmempool.cpp
index 4ccbcadefc..c6eaf661da 100644
--- a/src/txmempool.cpp
+++ b/src/txmempool.cpp
@@ -359,7 +359,6 @@ CTxMemPool::CTxMemPool(const CFeeRate& _minReasonableRelayFee) :
     nCheckFrequency = 0;
 
     minerPolicyEstimator = new CBlockPolicyEstimator(_minReasonableRelayFee);
-    minReasonableRelayFee = _minReasonableRelayFee;
 }
 
 CTxMemPool::~CTxMemPool()
@@ -1077,12 +1076,12 @@ CFeeRate CTxMemPool::GetMinFee(size_t sizelimit) const {
         rollingMinimumFeeRate = rollingMinimumFeeRate / pow(2.0, (time - lastRollingFeeUpdate) / halflife);
         lastRollingFeeUpdate = time;
 
-        if (rollingMinimumFeeRate < (double)minReasonableRelayFee.GetFeePerK() / 2) {
+        if (rollingMinimumFeeRate < (double)incrementalRelayFee.GetFeePerK() / 2) {
             rollingMinimumFeeRate = 0;
             return CFeeRate(0);
         }
     }
-    return std::max(CFeeRate(rollingMinimumFeeRate), minReasonableRelayFee);
+    return std::max(CFeeRate(rollingMinimumFeeRate), incrementalRelayFee);
 }
 
 void CTxMemPool::trackPackageRemoved(const CFeeRate& rate) {
@@ -1106,7 +1105,7 @@ void CTxMemPool::TrimToSize(size_t sizelimit, std::vector<uint256>* pvNoSpendsRe
         // to have 0 fee). This way, we don't allow txn to enter mempool with feerate
         // equal to txn which were removed with no block in between.
         CFeeRate removed(it->GetModFeesWithDescendants(), it->GetSizeWithDescendants());
-        removed += minReasonableRelayFee;
+        removed += incrementalRelayFee;
         trackPackageRemoved(removed);
         maxFeeRateRemoved = std::max(maxFeeRateRemoved, removed);
 
diff --git a/src/txmempool.h b/src/txmempool.h
index 7c68053f26..359babee55 100644
--- a/src/txmempool.h
+++ b/src/txmempool.h
@@ -425,8 +425,6 @@ private:
     uint64_t totalTxSize;      //!< sum of all mempool tx' byte sizes
     uint64_t cachedInnerUsage; //!< sum of dynamic memory usage of all the map elements (NOT the maps themselves)
 
-    CFeeRate minReasonableRelayFee;
-
     mutable int64_t lastRollingFeeUpdate;
     mutable bool blockSinceLastRollingFeeBump;
     mutable double rollingMinimumFeeRate; //!< minimum fee to get into the pool, decreases exponentially
@@ -505,9 +503,6 @@ public:
     std::map<uint256, std::pair<double, CAmount> > mapDeltas;
 
     /** Create a new CTxMemPool.
-     *  minReasonableRelayFee should be a feerate which is, roughly, somewhere
-     *  around what it "costs" to relay a transaction around the network and
-     *  below which we would reasonably say a transaction has 0-effective-fee.
      */
     CTxMemPool(const CFeeRate& _minReasonableRelayFee);
     ~CTxMemPool();
@@ -591,7 +586,7 @@ public:
 
     /** The minimum fee to get into the mempool, which may itself not be enough
       *  for larger-sized transactions.
-      *  The minReasonableRelayFee constructor arg is used to bound the time it
+      *  The incrementalRelayFee policy variable is used to bound the time it
       *  takes the fee rate to go back down all the way to 0. When the feerate
       *  would otherwise be half of this, it is set to 0 instead.
       */