Merge c6b94403bf9d5bf4fe9d5e5360b3d2c30a430d69 into 5f4422d68dc3530c353af1f87499de1c864b60ad

src/CMakeLists.txt

@@ -163,6 +163,7 @@ add_library(bitcoin_common STATIC EXCLUDE_FROM_ALL
   netbase.cpp
   outputtype.cpp
   policy/feerate.cpp
+  policy/fees/forecaster_util.cpp
   policy/policy.cpp
   pow.cpp
   protocol.cpp
@@ -277,8 +278,10 @@ add_library(bitcoin_node STATIC EXCLUDE_FROM_ALL
   node/warnings.cpp
   noui.cpp
   policy/ephemeral_policy.cpp
-  policy/fees.cpp
+  policy/fees/block_policy_estimator.cpp
-  policy/fees_args.cpp
+  policy/fees/block_policy_estimator_args.cpp
+  policy/fees/forecaster_man.cpp
+  policy/fees/mempool_forecaster.cpp
   policy/packages.cpp
   policy/rbf.cpp
   policy/settings.cpp

src/common/messages.cpp

@@ -6,7 +6,7 @@
 #include <common/messages.h>
 
 #include <common/types.h>
-#include <policy/fees.h>
+#include <policy/fees/block_policy_estimator.h>
 #include <node/types.h>
 #include <tinyformat.h>
 #include <util/strencodings.h>

src/init.cpp

@@ -57,8 +57,10 @@
 #include <node/miner.h>
 #include <node/peerman_args.h>
 #include <policy/feerate.h>
-#include <policy/fees.h>
+#include <policy/fees/block_policy_estimator.h>
-#include <policy/fees_args.h>
+#include <policy/fees/block_policy_estimator_args.h>
+#include <policy/fees/forecaster_man.h>
+#include <policy/fees/mempool_forecaster.h>
 #include <policy/policy.h>
 #include <policy/settings.h>
 #include <protocol.h>
@@ -328,13 +330,9 @@ void Shutdown(NodeContext& node)
         DumpMempool(*node.mempool, MempoolPath(*node.args));
     }
 
-    // Drop transactions we were still watching, record fee estimations and unregister
+    // Drop transactions we were still watching, record fee estimations.
-    // fee estimator from validation interface.
+    if (node.forecasterman) {
-    if (node.fee_estimator) {
+        node.forecasterman->GetBlockPolicyEstimator()->Flush();
-        node.fee_estimator->Flush();
-        if (node.validation_signals) {
-            node.validation_signals->UnregisterValidationInterface(node.fee_estimator.get());
-        }
     }
 
     // FlushStateToDisk generates a ChainStateFlushed callback, which we should avoid missing
@@ -389,7 +387,7 @@ void Shutdown(NodeContext& node)
         node.validation_signals->UnregisterAllValidationInterfaces();
     }
     node.mempool.reset();
-    node.fee_estimator.reset();
+    node.forecasterman.reset();
     node.chainman.reset();
     node.validation_signals.reset();
     node.scheduler.reset();
@@ -1500,22 +1498,6 @@ bool AppInitMain(NodeContext& node, interfaces::BlockAndHeaderTipInfo* tip_info)
                                               rng.rand64(),
                                               *node.addrman, *node.netgroupman, chainparams, args.GetBoolArg("-networkactive", true));
 
-    assert(!node.fee_estimator);
-    // Don't initialize fee estimation with old data if we don't relay transactions,
-    // as they would never get updated.
-    if (!peerman_opts.ignore_incoming_txs) {
-        bool read_stale_estimates = args.GetBoolArg("-acceptstalefeeestimates", DEFAULT_ACCEPT_STALE_FEE_ESTIMATES);
-        if (read_stale_estimates && (chainparams.GetChainType() != ChainType::REGTEST)) {
-            return InitError(strprintf(_("acceptstalefeeestimates is not supported on %s chain."), chainparams.GetChainTypeString()));
-        }
-        node.fee_estimator = std::make_unique<CBlockPolicyEstimator>(FeeestPath(args), read_stale_estimates);
-
-        // Flush estimates to disk periodically
-        CBlockPolicyEstimator* fee_estimator = node.fee_estimator.get();
-        scheduler.scheduleEvery([fee_estimator] { fee_estimator->FlushFeeEstimates(); }, FEE_FLUSH_INTERVAL);
-        validation_signals.RegisterValidationInterface(fee_estimator);
-    }
-
     for (const std::string& socket_addr : args.GetArgs("-bind")) {
         std::string host_out;
         uint16_t port_out{0};
@@ -1730,6 +1712,26 @@ bool AppInitMain(NodeContext& node, interfaces::BlockAndHeaderTipInfo* tip_info)
 
     ChainstateManager& chainman = *Assert(node.chainman);
 
+    assert(!node.forecasterman);
+    // Don't initialize fee estimation with old data if we don't relay transactions,
+    // as they would never get updated.
+    if (!peerman_opts.ignore_incoming_txs) {
+        bool read_stale_estimates = args.GetBoolArg("-acceptstalefeeestimates", DEFAULT_ACCEPT_STALE_FEE_ESTIMATES);
+        if (read_stale_estimates && (chainparams.GetChainType() != ChainType::REGTEST)) {
+            return InitError(strprintf(_("acceptstalefeeestimates is not supported on %s chain."), chainparams.GetChainTypeString()));
+        }
+        node.forecasterman = std::make_unique<FeeRateForecasterManager>();
+        auto mempool_forecaster = std::make_shared<MemPoolForecaster>(node.mempool.get(), &(chainman.ActiveChainstate()));
+        node.forecasterman->RegisterForecaster(mempool_forecaster);
+        auto block_policy_estimator = std::make_shared<CBlockPolicyEstimator>(FeeestPath(args), read_stale_estimates);
+        validation_signals.RegisterSharedValidationInterface(block_policy_estimator);
+        // Flush block policy estimates to disk periodically
+        scheduler.scheduleEvery([block_policy_estimator] { block_policy_estimator->FlushFeeEstimates(); }, FEE_FLUSH_INTERVAL);
+
+        // Register block policy estimator to forecaster manager
+        node.forecasterman->RegisterForecaster(block_policy_estimator);
+    }
+
     assert(!node.peerman);
     node.peerman = PeerManager::make(*node.connman, *node.addrman,
                                      node.banman.get(), chainman,

src/net_processing.cpp

@@ -27,7 +27,7 @@
 #include <node/txdownloadman.h>
 #include <node/txreconciliation.h>
 #include <node/warnings.h>
-#include <policy/fees.h>
+#include <policy/fees/block_policy_estimator.h>
 #include <policy/policy.h>
 #include <policy/settings.h>
 #include <primitives/block.h>

src/node/context.cpp

@@ -15,7 +15,7 @@
 #include <netgroup.h>
 #include <node/kernel_notifications.h>
 #include <node/warnings.h>
-#include <policy/fees.h>
+#include <policy/fees/forecaster_man.h>
 #include <scheduler.h>
 #include <txmempool.h>
 #include <validation.h>

src/node/context.h

@@ -16,7 +16,7 @@ class ArgsManager;
 class AddrMan;
 class BanMan;
 class BaseIndex;
-class CBlockPolicyEstimator;
+class FeeRateForecasterManager;
 class CConnman;
 class ValidationSignals;
 class CScheduler;
@@ -67,7 +67,7 @@ struct NodeContext {
     std::unique_ptr<CConnman> connman;
     std::unique_ptr<CTxMemPool> mempool;
     std::unique_ptr<const NetGroupManager> netgroupman;
-    std::unique_ptr<CBlockPolicyEstimator> fee_estimator;
+    std::unique_ptr<FeeRateForecasterManager> forecasterman;
     std::unique_ptr<PeerManager> peerman;
     std::unique_ptr<ChainstateManager> chainman;
     std::unique_ptr<BanMan> banman;

src/node/interfaces.cpp

@@ -40,7 +40,8 @@
 #include <node/types.h>
 #include <node/warnings.h>
 #include <policy/feerate.h>
-#include <policy/fees.h>
+#include <policy/fees/block_policy_estimator.h>
+#include <policy/fees/forecaster_man.h>
 #include <policy/policy.h>
 #include <policy/rbf.h>
 #include <policy/settings.h>
@@ -739,13 +740,13 @@ public:
     }
     CFeeRate estimateSmartFee(int num_blocks, bool conservative, FeeCalculation* calc) override
     {
-        if (!m_node.fee_estimator) return {};
+        if (!m_node.forecasterman) return {};
-        return m_node.fee_estimator->estimateSmartFee(num_blocks, calc, conservative);
+        return m_node.forecasterman->GetBlockPolicyEstimator()->estimateSmartFee(num_blocks, calc, conservative);
     }
     unsigned int estimateMaxBlocks() override
     {
-        if (!m_node.fee_estimator) return 0;
+        if (!m_node.forecasterman) return 0;
-        return m_node.fee_estimator->HighestTargetTracked(FeeEstimateHorizon::LONG_HALFLIFE);
+        return m_node.forecasterman->GetBlockPolicyEstimator()->HighestTargetTracked(FeeEstimateHorizon::LONG_HALFLIFE);
     }
     CFeeRate mempoolMinFee() override
     {

src/policy/fees/block_policy_estimator.cpp

@@ -3,13 +3,14 @@
 // Distributed under the MIT software license, see the accompanying
 // file COPYING or http://www.opensource.org/licenses/mit-license.php.
 
-#include <policy/fees.h>
+#include <policy/fees/block_policy_estimator.h>
 
 #include <common/system.h>
 #include <consensus/amount.h>
 #include <kernel/mempool_entry.h>
 #include <logging.h>
 #include <policy/feerate.h>
+#include <policy/fees/forecaster_util.h>
 #include <primitives/transaction.h>
 #include <random.h>
 #include <serialize.h>
@@ -540,7 +541,7 @@ bool CBlockPolicyEstimator::_removeTx(const uint256& hash, bool inBlock)
 }
 
 CBlockPolicyEstimator::CBlockPolicyEstimator(const fs::path& estimation_filepath, const bool read_stale_estimates)
-    : m_estimation_filepath{estimation_filepath}
+    : Forecaster(ForecastType::BLOCK_POLICY), m_estimation_filepath{estimation_filepath}
 {
     static_assert(MIN_BUCKET_FEERATE > 0, "Min feerate must be nonzero");
     size_t bucketIndex = 0;
@@ -723,6 +724,29 @@ CFeeRate CBlockPolicyEstimator::estimateFee(int confTarget) const
     return estimateRawFee(confTarget, DOUBLE_SUCCESS_PCT, FeeEstimateHorizon::MED_HALFLIFE);
 }
 
+ForecastResult CBlockPolicyEstimator::EstimateFee(ConfirmationTarget& target)
+{
+    ForecastResult::ForecastResponse response;
+    response.forecaster = ForecastType::BLOCK_POLICY;
+    if (target.type != ConfirmationTargetType::BLOCKS) {
+        return ForecastResult(response, "Incorrect Confirmation target, expecting blocks");
+    }
+    FeeCalculation feeCalcConservative;
+    CFeeRate feerate_conservative{estimateSmartFee(target.value, &feeCalcConservative, /**conservative**/ true)};
+    FeeCalculation feeCalcEconomical;
+    CFeeRate feerate_economical{estimateSmartFee(target.value, &feeCalcEconomical, /**conservative**/ false)};
+    response.current_block_height = feeCalcEconomical.bestheight;
+    if (feerate_conservative == CFeeRate(0) || feerate_economical == CFeeRate(0)) {
+        return ForecastResult(response, "Insufficient data or no feerate found");
+    }
+    // Note: size can be any positive non-zero integer; the evaluated fee/size will result in the same fee rate,
+    // and we only care that the fee rate remains consistent.
+    int32_t size = 1000;
+    response.low_priority = FeeFrac(feerate_economical.GetFee(size), size);
+    response.high_priority = FeeFrac(feerate_conservative.GetFee(size), size);
+    return ForecastResult(response);
+}
+
 CFeeRate CBlockPolicyEstimator::estimateRawFee(int confTarget, double successThreshold, FeeEstimateHorizon horizon, EstimationResult* result) const
 {
     TxConfirmStats* stats = nullptr;
@@ -874,6 +898,7 @@ CFeeRate CBlockPolicyEstimator::estimateSmartFee(int confTarget, FeeCalculation
     if (feeCalc) {
         feeCalc->desiredTarget = confTarget;
         feeCalc->returnedTarget = confTarget;
+        feeCalc->bestheight = nBestSeenHeight;
     }
 
     double median = -1;

src/policy/fees/block_policy_estimator.h

@@ -2,11 +2,12 @@
 // Copyright (c) 2009-2022 The Bitcoin Core developers
 // Distributed under the MIT software license, see the accompanying
 // file COPYING or http://www.opensource.org/licenses/mit-license.php.
-#ifndef BITCOIN_POLICY_FEES_H
+#ifndef BITCOIN_POLICY_FEES_BLOCK_POLICY_ESTIMATOR_H
-#define BITCOIN_POLICY_FEES_H
+#define BITCOIN_POLICY_FEES_BLOCK_POLICY_ESTIMATOR_H
 
 #include <consensus/amount.h>
 #include <policy/feerate.h>
+#include <policy/fees/forecaster.h>
 #include <random.h>
 #include <sync.h>
 #include <threadsafety.h>
@@ -36,10 +37,14 @@ static constexpr std::chrono::hours MAX_FILE_AGE{60};
 static constexpr bool DEFAULT_ACCEPT_STALE_FEE_ESTIMATES{false};
 
 class AutoFile;
+class ForecastResult;
 class TxConfirmStats;
+
+struct ConfirmationTarget;
 struct RemovedMempoolTransactionInfo;
 struct NewMempoolTransactionInfo;
 
+
 /* Identifier for each of the 3 different TxConfirmStats which will track
  * history over different time horizons. */
 enum class FeeEstimateHorizon {
@@ -95,6 +100,7 @@ struct FeeCalculation
     FeeReason reason = FeeReason::NONE;
     int desiredTarget = 0;
     int returnedTarget = 0;
+    unsigned int bestheight{0};
 };
 
 /** \class CBlockPolicyEstimator
@@ -145,7 +151,7 @@ struct FeeCalculation
  * a certain number of blocks.  Every time a block is added to the best chain, this class records
  * stats on the transactions included in that block
  */
-class CBlockPolicyEstimator : public CValidationInterface
+class CBlockPolicyEstimator : public Forecaster, public CValidationInterface
 {
 private:
     /** Track confirm delays up to 12 blocks for short horizon */
@@ -271,6 +277,10 @@ protected:
     void MempoolTransactionsRemovedForBlock(const std::vector<RemovedMempoolTransactionInfo>& txs_removed_for_block, unsigned int nBlockHeight) override
         EXCLUSIVE_LOCKS_REQUIRED(!m_cs_fee_estimator);
 
+    /** Overridden from Forecaster. */
+    ForecastResult EstimateFee(ConfirmationTarget& target) override
+        EXCLUSIVE_LOCKS_REQUIRED(!m_cs_fee_estimator);
+
 private:
     mutable Mutex m_cs_fee_estimator;
 
@@ -342,4 +352,4 @@ private:
     FastRandomContext& insecure_rand GUARDED_BY(m_insecure_rand_mutex);
 };
 
-#endif // BITCOIN_POLICY_FEES_H
+#endif // BITCOIN_POLICY_FEES_BLOCK_POLICY_ESTIMATOR_H

src/policy/fees/block_policy_estimator_args.cpp

@@ -2,7 +2,7 @@
 // Distributed under the MIT software license, see the accompanying
 // file COPYING or http://www.opensource.org/licenses/mit-license.php.
 
-#include <policy/fees_args.h>
+#include <policy/fees/block_policy_estimator_args.h>
 
 #include <common/args.h>
 

src/policy/fees/block_policy_estimator_args.h

@@ -2,8 +2,8 @@
 // Distributed under the MIT software license, see the accompanying
 // file COPYING or http://www.opensource.org/licenses/mit-license.php.
 
-#ifndef BITCOIN_POLICY_FEES_ARGS_H
+#ifndef BITCOIN_POLICY_FEES_BLOCK_POLICY_ESTIMATOR_ARGS_H
-#define BITCOIN_POLICY_FEES_ARGS_H
+#define BITCOIN_POLICY_FEES_BLOCK_POLICY_ESTIMATOR_ARGS_H
 
 #include <util/fs.h>
 
@@ -12,4 +12,4 @@ class ArgsManager;
 /** @return The fee estimates data file path. */
 fs::path FeeestPath(const ArgsManager& argsman);
 
-#endif // BITCOIN_POLICY_FEES_ARGS_H
+#endif // BITCOIN_POLICY_FEES_BLOCK_POLICY_ESTIMATOR_ARGS_H

src/policy/fees/forecaster.h

@@ -0,0 +1,36 @@
+// Copyright (c) 2025 The Bitcoin Core developers
+// Distributed under the MIT software license. See the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#ifndef BITCOIN_POLICY_FEES_FORECASTER_H
+#define BITCOIN_POLICY_FEES_FORECASTER_H
+
+#include <policy/fees/forecaster_util.h>
+
+/** \class Forecaster
+ * Abstract base class for fee rate forecasters.
+ */
+class Forecaster
+{
+protected:
+    const ForecastType m_forecastType;
+
+public:
+    Forecaster(ForecastType forecastType) : m_forecastType(forecastType) {}
+
+    ForecastType GetForecastType() const { return m_forecastType; }
+
+    /**
+     * Forecast the fee rate required for package to confirm within
+     * a specified target.
+     *
+     * This pure virtual function must be overridden by derived classes.
+     * @param target The confirmation target for which to forecast the feerate for.
+     * @return ForecastResult containing the forecasted fee rate.
+     */
+    virtual ForecastResult EstimateFee(ConfirmationTarget& target) = 0;
+
+    virtual ~Forecaster() = default;
+};
+
+#endif // BITCOIN_POLICY_FEES_FORECASTER_H

src/policy/fees/forecaster_man.cpp

@@ -0,0 +1,67 @@
+// Copyright (c) 2025 The Bitcoin Core developers
+// Distributed under the MIT software license. See the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#include <logging.h>
+#include <policy/fees/block_policy_estimator.h>
+#include <policy/fees/forecaster.h>
+#include <policy/fees/forecaster_man.h>
+#include <policy/fees/forecaster_util.h>
+
+#include <algorithm>
+#include <utility>
+
+void FeeRateForecasterManager::RegisterForecaster(std::shared_ptr<Forecaster> forecaster)
+{
+    forecasters.emplace(forecaster->GetForecastType(), forecaster);
+}
+
+CBlockPolicyEstimator* FeeRateForecasterManager::GetBlockPolicyEstimator()
+{
+    Assume(forecasters.contains(ForecastType::BLOCK_POLICY));
+    Forecaster* block_policy_estimator = forecasters.find(ForecastType::BLOCK_POLICY)->second.get();
+    return dynamic_cast<CBlockPolicyEstimator*>(block_policy_estimator);
+}
+
+std::pair<std::optional<ForecastResult>, std::vector<std::string>> FeeRateForecasterManager::GetFeeRateForecast(ConfirmationTarget& target)
+{
+    std::vector<std::string> err_messages;
+    ForecastResult selected_forecast;
+
+    for (const auto& forecaster : forecasters) {
+        auto curr_forecast = forecaster.second->EstimateFee(target);
+
+        if (curr_forecast.GetError().has_value()) {
+            err_messages.emplace_back(
+                strprintf("%s: %s", forecastTypeToString(forecaster.first), curr_forecast.GetError().value_or("")));
+        }
+
+        // Handle case where the block policy estimator does not have enough data for fee estimates.
+        if (curr_forecast.Empty() && forecaster.first == ForecastType::BLOCK_POLICY) {
+            return {std::nullopt, err_messages};
+        }
+
+        if (!curr_forecast.Empty()) {
+            if (selected_forecast.Empty()) {
+                // If there's no selected forecast, choose curr_forecast as selected_forecast.
+                selected_forecast = curr_forecast;
+            } else {
+                // Otherwise, choose the smaller as selected_forecast.
+                selected_forecast = std::min(selected_forecast, curr_forecast);
+            }
+        }
+    }
+
+    if (!selected_forecast.Empty()) {
+        LogDebug(BCLog::ESTIMATEFEE,
+                 "FeeEst %s: Block height %s, low priority fee rate %s %s/kvB, high priority fee rate %s %s/kvB.\n",
+                 forecastTypeToString(selected_forecast.GetResponse().forecaster),
+                 selected_forecast.GetResponse().current_block_height,
+                 CFeeRate(selected_forecast.GetResponse().low_priority.fee, selected_forecast.GetResponse().low_priority.size).GetFeePerK(),
+                 CURRENCY_ATOM,
+                 CFeeRate(selected_forecast.GetResponse().high_priority.fee, selected_forecast.GetResponse().high_priority.size).GetFeePerK(),
+                 CURRENCY_ATOM);
+    }
+
+    return {selected_forecast, err_messages};
+}

src/policy/fees/forecaster_man.h

@@ -0,0 +1,57 @@
+// Copyright (c) 2025 The Bitcoin Core developers
+// Distributed under the MIT software license. See the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#ifndef BITCOIN_POLICY_FEES_FORECASTER_MAN_H
+#define BITCOIN_POLICY_FEES_FORECASTER_MAN_H
+
+#include <memory>
+#include <optional>
+#include <unordered_map>
+
+class CBlockPolicyEstimator;
+class Forecaster;
+class ForecastResult;
+
+struct ConfirmationTarget;
+
+enum class ForecastType;
+
+/** \class FeeRateForecasterManager
+ * Module for managing and utilising multiple fee rate forecasters to provide a forecast for a target.
+ *
+ * The FeeRateForecasterManager class allows for the registration of multiple fee rate
+ * forecasters.
+ */
+class FeeRateForecasterManager
+{
+private:
+    //! Map of all registered forecasters to their shared pointers.
+    std::unordered_map<ForecastType, std::shared_ptr<Forecaster>> forecasters;
+
+public:
+    /**
+     * Register a forecaster to provide fee rate estimates.
+     *
+     * @param[in] forecaster shared pointer to a Forecaster instance.
+     */
+    void RegisterForecaster(std::shared_ptr<Forecaster> forecaster);
+
+    /*
+     * Return the pointer to block policy estimator.
+     */
+    CBlockPolicyEstimator* GetBlockPolicyEstimator();
+
+    /**
+     * Get a fee rate estimate from all registered forecasters for a given confirmation target.
+     *
+     * Polls all registered forecasters and selects the lowest fee rate
+     * estimate with acceptable confidence.
+     *
+     * @param[in] target The target within which the transaction should be confirmed.
+     * @return A pair consisting of the forecast result and a vector of forecaster names.
+     */
+    std::pair<std::optional<ForecastResult>, std::vector<std::string>> GetFeeRateForecast(ConfirmationTarget& target);
+};
+
+#endif // BITCOIN_POLICY_FEES_FORECASTER_MAN_H

src/policy/fees/forecaster_util.cpp

@@ -0,0 +1,57 @@
+// Copyright (c) 2025 The Bitcoin Core developers
+// Distributed under the MIT software license. See the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#include <policy/fees/forecaster_util.h>
+#include <policy/policy.h>
+
+#include <algorithm>
+
+Percentiles CalculatePercentiles(const std::vector<FeeFrac>& package_feerates, const int32_t total_weight)
+{
+    if (package_feerates.empty()) return Percentiles{};
+    int32_t accumulated_weight{0};
+    const int32_t p25_weight = 0.25 * total_weight;
+    const int32_t p50_weight = 0.50 * total_weight;
+    const int32_t p75_weight = 0.75 * total_weight;
+    const int32_t p95_weight = 0.95 * total_weight;
+    auto last_tracked_feerate = package_feerates.front();
+    auto percentiles = Percentiles{};
+
+    // Process histogram entries while maintaining monotonicity
+    for (const auto& curr_feerate : package_feerates) {
+        accumulated_weight += curr_feerate.size * WITNESS_SCALE_FACTOR;
+        // Maintain monotonicity by taking the minimum between the current and last tracked fee rate
+        last_tracked_feerate = std::min(last_tracked_feerate, curr_feerate, [](const FeeFrac& a, const FeeFrac& b) {
+            return std::is_lt(FeeRateCompare(a, b));
+        });
+        if (accumulated_weight >= p25_weight && percentiles.p25.IsEmpty()) {
+            percentiles.p25 = last_tracked_feerate;
+        }
+        if (accumulated_weight >= p50_weight && percentiles.p50.IsEmpty()) {
+            percentiles.p50 = last_tracked_feerate;
+        }
+        if (accumulated_weight >= p75_weight && percentiles.p75.IsEmpty()) {
+            percentiles.p75 = last_tracked_feerate;
+        }
+        if (accumulated_weight >= p95_weight && percentiles.p95.IsEmpty()) {
+            percentiles.p95 = last_tracked_feerate;
+            break; // Early exit once all percentiles are calculated
+        }
+    }
+
+    // Return empty percentiles if we couldn't calculate the 95th percentile.
+    return percentiles.p95.IsEmpty() ? Percentiles{} : percentiles;
+}
+
+std::string forecastTypeToString(ForecastType forecastType)
+{
+    switch (forecastType) {
+    case ForecastType::MEMPOOL_FORECAST:
+        return std::string("Mempool Forecast");
+    case ForecastType::BLOCK_POLICY:
+        return std::string("Block Policy Estimator");
+    }
+    // no default case, so the compiler can warn about missing cases
+    assert(false);
+}

src/policy/fees/forecaster_util.h

@@ -0,0 +1,161 @@
+// Copyright (c) 2025 The Bitcoin Core developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#ifndef BITCOIN_POLICY_FEES_FORECASTER_UTIL_H
+#define BITCOIN_POLICY_FEES_FORECASTER_UTIL_H
+
+#include <util/feefrac.h>
+
+#include <optional>
+#include <string>
+
+/**
+ * @enum ForecastType
+ * Identifier for fee rate forecasters.
+ */
+enum class ForecastType {
+    BLOCK_POLICY,
+    MEMPOOL_FORECAST,
+};
+
+/**
+ * @class ForecastResult
+ * Represents the response returned by a fee rate forecaster.
+ */
+class ForecastResult
+{
+public:
+    /**
+     * @struct ForecastResponse
+     * Contains fee rate forecast metadata.
+     */
+    struct ForecastResponse {
+        /**
+         * An estimated fee rate as a result of a forecast for economical transactions.
+         * This value is sufficient to confirm a package within the specified target.
+         */
+        FeeFrac low_priority;
+
+        /**
+         * An estimated fee rate as a result of forecast for high-priority transactions.
+         * This value is for users willing to pay more to increase the likelihood of
+         * confirmation within the specified target.
+         */
+        FeeFrac high_priority;
+
+        /**
+         * The chain tip at which the forecast was made.
+         */
+        unsigned int current_block_height{0};
+        /* This identifies which forecaster is providing this feerate forecast */
+        ForecastType forecaster;
+    };
+
+    /**
+     * Default ForecastResult constructor.
+     */
+    ForecastResult() {}
+
+    /**
+     * Constructs a ForecastResult object.
+     * @param response The forecast response data.
+     * @param error An optional error message (default: nullopt).
+     */
+    ForecastResult(ForecastResponse response, std::optional<std::string> error = std::nullopt)
+        : m_response(std::move(response)), m_error(std::move(error))
+    {
+    }
+
+    /**
+     * Checks if the forecast response is empty.
+     * @return true if both low and high priority forecast estimates are empty, false otherwise.
+     */
+    bool Empty() const
+    {
+        return m_response.low_priority.IsEmpty() && m_response.high_priority.IsEmpty();
+    }
+
+    /**
+     * Overloaded less than operator which compares two ForecastResult objects based on
+     * their high priority estimates.
+     * @param other The other ForecastResult object to compare with.
+     * @return true if the current object's high priority estimate is less than the other, false otherwise.
+     */
+    bool operator<(const ForecastResult& other) const
+    {
+        return m_response.high_priority << other.m_response.high_priority;
+    }
+
+    /**
+     * Retrieves the forecast response.
+     * @return A reference to the forecast response metadata.
+     */
+    const ForecastResponse& GetResponse() const
+    {
+        return m_response;
+    }
+
+    /**
+     * Retrieves the error message, if any.
+     * @return An optional string containing the error message.
+     */
+    const std::optional<std::string>& GetError() const
+    {
+        return m_error;
+    }
+
+private:
+    ForecastResponse m_response;        ///< The forecast response data.
+    std::optional<std::string> m_error; ///< Optional error message.
+};
+
+/**
+ * @enum ConfirmationTargetType
+ * Defines the types of confirmation targets for fee rate forecasters.
+ */
+enum class ConfirmationTargetType {
+    BLOCKS, /**< Forecasters providing estimates for a specific number of blocks use this type. */
+};
+
+/**
+ * @struct ConfirmationTarget
+ * Represents the input for a parameter of fee rate forecaster.
+ */
+struct ConfirmationTarget {
+    unsigned int value;
+    ConfirmationTargetType type;
+};
+
+// Block percentiles fee rate (in sat/kvB).
+struct Percentiles {
+    FeeFrac p25; // 25th percentile
+    FeeFrac p50; // 50th percentile
+    FeeFrac p75; // 75th percentile
+    FeeFrac p95; // 5th percentile
+
+    Percentiles() = default;
+
+    bool empty() const
+    {
+        return p25.IsEmpty() && p50.IsEmpty() && p75.IsEmpty() && p95.IsEmpty();
+    }
+};
+
+/**
+ * Calculates the percentile fee rates from a given vector of fee rates.
+ *
+ * This function assumes that the fee rates in the input vector are sorted in descending order
+ * based on mining score priority. It ensures that the calculated percentile fee rates
+ * are monotonically decreasing by filtering out outliers. Outliers can occur when
+ * the mining score of a transaction increases due to the inclusion of its ancestors
+ * in different transaction packages.
+ *
+ * @param[in] package_feerates A vector containing fee rates and their corresponding virtual sizes.
+ * @return Percentiles object containing the calculated percentile fee rates.
+ */
+Percentiles CalculatePercentiles(const std::vector<FeeFrac>& package_feerates, const int32_t total_weight);
+
+std::string forecastTypeToString(ForecastType forecastType);
+
+#endif // BITCOIN_POLICY_FEES_FORECASTER_UTIL_H

src/policy/fees/mempool_forecaster.cpp

@@ -0,0 +1,71 @@
+// Copyright (c) 2024 The Bitcoin Core developers
+// Distributed under the MIT software license. See the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#include <logging.h>
+#include <node/miner.h>
+#include <policy/fees/forecaster.h>
+#include <policy/fees/forecaster_util.h>
+#include <policy/fees/mempool_forecaster.h>
+#include <policy/policy.h>
+#include <validation.h>
+
+ForecastResult MemPoolForecaster::EstimateFee(ConfirmationTarget& target)
+{
+    ForecastResult::ForecastResponse response;
+    response.forecaster = m_forecastType;
+    LOCK2(cs_main, m_mempool->cs);
+    auto activeTip = m_chainstate->m_chainman.ActiveTip();
+    if (!activeTip) {
+        return ForecastResult(response, "No active chainstate available");
+    }
+    response.current_block_height = static_cast<unsigned int>(activeTip->nHeight);
+
+    if (target.type != ConfirmationTargetType::BLOCKS) {
+        return ForecastResult(response, "Forecaster can only provide an estimate for block targets");
+    }
+    if (target.value > MEMPOOL_FORECAST_MAX_TARGET) {
+        return ForecastResult(response, strprintf(
+                                            "Confirmation target %s exceeds the maximum limit of %s. mempool conditions might change, "
+                                            "making forecasts above %s block may be unreliable",
+                                            target.value, MEMPOOL_FORECAST_MAX_TARGET, MEMPOOL_FORECAST_MAX_TARGET));
+    }
+
+    const auto cached_estimate = cache.get();
+    if (cached_estimate) {
+        response.low_priority = cached_estimate->p75;
+        response.high_priority = cached_estimate->p50;
+        return ForecastResult(response);
+    }
+
+    node::BlockAssembler::Options options;
+    options.test_block_validity = false;
+    node::BlockAssembler assembler(*m_chainstate, m_mempool, options);
+
+    const auto pblocktemplate = assembler.CreateNewBlock();
+    const auto& m_package_feerates = pblocktemplate->m_package_feerates;
+    if (m_package_feerates.empty()) {
+        return ForecastResult(response, "No enough transactions in the mempool to provide a fee rate forecast");
+    }
+
+    const auto percentiles = CalculatePercentiles(m_package_feerates, DEFAULT_BLOCK_MAX_WEIGHT);
+    if (percentiles.empty()) {
+        return ForecastResult(response, "Forecaster unable to provide an estimate due to insufficient data");
+    }
+
+    LogDebug(BCLog::ESTIMATEFEE,
+             "FeeEstimation: %s: Block height %s, 25th percentile fee rate: %s %s/kvB, "
+             "50th percentile fee rate: %s %s/kvB, 75th percentile fee rate: %s %s/kvB, "
+             "95th percentile fee rate: %s %s/kvB\n",
+             forecastTypeToString(m_forecastType), response.current_block_height,
+             CFeeRate(percentiles.p25.fee, percentiles.p25.size).GetFeePerK(), CURRENCY_ATOM,
+             CFeeRate(percentiles.p50.fee, percentiles.p50.size).GetFeePerK(), CURRENCY_ATOM,
+             CFeeRate(percentiles.p75.fee, percentiles.p75.size).GetFeePerK(), CURRENCY_ATOM,
+             CFeeRate(percentiles.p95.fee, percentiles.p95.size).GetFeePerK(), CURRENCY_ATOM);
+
+    cache.update(percentiles);
+    response.low_priority = percentiles.p75;
+    response.high_priority = percentiles.p50;
+
+    return ForecastResult(response);
+}

src/policy/fees/mempool_forecaster.h

@@ -0,0 +1,92 @@
+// Copyright (c) 2024 The Bitcoin Core developers
+// Distributed under the MIT software license. See the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#ifndef BITCOIN_POLICY_FEES_MEMPOOL_FORECASTER_H
+#define BITCOIN_POLICY_FEES_MEMPOOL_FORECASTER_H
+
+
+#include <logging.h>
+#include <policy/fees/forecaster.h>
+#include <policy/fees/forecaster_util.h>
+#include <sync.h>
+#include <util/time.h>
+
+#include <chrono>
+
+class Chainstate;
+class CTxMemPool;
+
+struct ConfirmationTarget;
+
+// Fee rate estimates above this confirmation target are not reliable,
+// mempool condition might likely change.
+constexpr int MEMPOOL_FORECAST_MAX_TARGET{2};
+constexpr std::chrono::seconds CACHE_LIFE{30};
+
+/**
+ * CachedMempoolEstimates holds a cache of recent forecast.
+ * We only provide fresh estimates if the last cached fee rate
+ * forecast ages more than CACHE_LIFE.
+ */
+struct CachedMempoolEstimates {
+private:
+    mutable Mutex cache_mutex;
+    Percentiles fee_estimate GUARDED_BY(cache_mutex);
+    NodeClock::time_point last_updated GUARDED_BY(cache_mutex){NodeClock::now() - CACHE_LIFE - std::chrono::seconds(1)};
+
+    bool isStale() const EXCLUSIVE_LOCKS_REQUIRED(cache_mutex)
+    {
+        AssertLockHeld(cache_mutex);
+        return (last_updated + CACHE_LIFE) < NodeClock::now();
+    }
+
+public:
+    CachedMempoolEstimates() = default;
+    CachedMempoolEstimates(const CachedMempoolEstimates&) = delete;
+    CachedMempoolEstimates& operator=(const CachedMempoolEstimates&) = delete;
+
+    std::optional<Percentiles> get() const EXCLUSIVE_LOCKS_REQUIRED(!cache_mutex)
+    {
+        LOCK(cache_mutex);
+        if (isStale()) return std::nullopt;
+        LogDebug(BCLog::ESTIMATEFEE, "%s: cache is not stale, using cached value\n", forecastTypeToString(ForecastType::MEMPOOL_FORECAST));
+        return fee_estimate;
+    }
+
+    void update(const Percentiles& new_fee_estimate) EXCLUSIVE_LOCKS_REQUIRED(!cache_mutex)
+    {
+        LOCK(cache_mutex);
+        fee_estimate = new_fee_estimate;
+        last_updated = NodeClock::now();
+        LogDebug(BCLog::ESTIMATEFEE, "%s: updated cache\n", forecastTypeToString(ForecastType::MEMPOOL_FORECAST));
+    }
+};
+
+/** \class MemPoolForecaster
+ * This fee estimate forecaster estimates the fee rate that a transaction will pay
+ * to be included in a block as soon as possible.
+ * It uses the unconfirmed transactions in the mempool to generate the next block template
+ * that will likely be mined.
+ * The percentile fee rate's are computed, and the bottom 25th percentile and 50th percentile fee rate's are returned.
+ */
+class MemPoolForecaster : public Forecaster
+{
+public:
+    MemPoolForecaster(const CTxMemPool* mempool, Chainstate* chainstate)
+        : Forecaster(ForecastType::MEMPOOL_FORECAST), m_mempool(mempool), m_chainstate(chainstate) {};
+    ~MemPoolForecaster() = default;
+
+    /**
+     * Estimate the fee rate from mempool transactions given a confirmation target.
+     * @param[in] target The confirmation target to provide estimate for.
+     * @return The forecasted fee rates.
+     */
+    ForecastResult EstimateFee(ConfirmationTarget& target) override;
+
+private:
+    const CTxMemPool* m_mempool;
+    Chainstate* m_chainstate;
+    mutable CachedMempoolEstimates cache;
+};
+#endif // BITCOIN_POLICY_FEES_MEMPOOL_FORECASTER_H

src/qt/sendcoinsdialog.cpp

@@ -21,7 +21,7 @@
 #include <key_io.h>
 #include <node/interface_ui.h>
 #include <node/types.h>
-#include <policy/fees.h>
+#include <policy/fees/block_policy_estimator.h>
 #include <txmempool.h>
 #include <validation.h>
 #include <wallet/coincontrol.h>

src/rpc/fees.cpp

@@ -7,7 +7,8 @@
 #include <core_io.h>
 #include <node/context.h>
 #include <policy/feerate.h>
-#include <policy/fees.h>
+#include <policy/fees/block_policy_estimator.h>
+#include <policy/fees/forecaster_man.h>
 #include <rpc/protocol.h>
 #include <rpc/request.h>
 #include <rpc/server.h>
@@ -59,12 +60,12 @@ static RPCHelpMan estimatesmartfee()
         },
         [&](const RPCHelpMan& self, const JSONRPCRequest& request) -> UniValue
         {
-            CBlockPolicyEstimator& fee_estimator = EnsureAnyFeeEstimator(request.context);
+            CBlockPolicyEstimator& block_policy_fee_estimator = *(EnsureAnyForecasterMan(request.context).GetBlockPolicyEstimator());
             const NodeContext& node = EnsureAnyNodeContext(request.context);
             const CTxMemPool& mempool = EnsureMemPool(node);
 
             CHECK_NONFATAL(mempool.m_opts.signals)->SyncWithValidationInterfaceQueue();
-            unsigned int max_target = fee_estimator.HighestTargetTracked(FeeEstimateHorizon::LONG_HALFLIFE);
+            unsigned int max_target = block_policy_fee_estimator.HighestTargetTracked(FeeEstimateHorizon::LONG_HALFLIFE);
             unsigned int conf_target = ParseConfirmTarget(request.params[0], max_target);
             bool conservative = false;
             if (!request.params[1].isNull()) {
@@ -78,7 +79,7 @@ static RPCHelpMan estimatesmartfee()
             UniValue result(UniValue::VOBJ);
             UniValue errors(UniValue::VARR);
             FeeCalculation feeCalc;
-            CFeeRate feeRate{fee_estimator.estimateSmartFee(conf_target, &feeCalc, conservative)};
+            CFeeRate feeRate{block_policy_fee_estimator.estimateSmartFee(conf_target, &feeCalc, conservative)};
             if (feeRate != CFeeRate(0)) {
                 CFeeRate min_mempool_feerate{mempool.GetMinFee()};
                 CFeeRate min_relay_feerate{mempool.m_opts.min_relay_feerate};
@@ -150,11 +151,11 @@ static RPCHelpMan estimaterawfee()
         },
         [&](const RPCHelpMan& self, const JSONRPCRequest& request) -> UniValue
         {
-            CBlockPolicyEstimator& fee_estimator = EnsureAnyFeeEstimator(request.context);
+            CBlockPolicyEstimator& block_policy_fee_estimator = *(EnsureAnyForecasterMan(request.context).GetBlockPolicyEstimator());
             const NodeContext& node = EnsureAnyNodeContext(request.context);
 
             CHECK_NONFATAL(node.validation_signals)->SyncWithValidationInterfaceQueue();
-            unsigned int max_target = fee_estimator.HighestTargetTracked(FeeEstimateHorizon::LONG_HALFLIFE);
+            unsigned int max_target = block_policy_fee_estimator.HighestTargetTracked(FeeEstimateHorizon::LONG_HALFLIFE);
             unsigned int conf_target = ParseConfirmTarget(request.params[0], max_target);
             double threshold = 0.95;
             if (!request.params[1].isNull()) {
@@ -171,9 +172,9 @@ static RPCHelpMan estimaterawfee()
                 EstimationResult buckets;
 
                 // Only output results for horizons which track the target
-                if (conf_target > fee_estimator.HighestTargetTracked(horizon)) continue;
+                if (conf_target > block_policy_fee_estimator.HighestTargetTracked(horizon)) continue;
 
-                feeRate = fee_estimator.estimateRawFee(conf_target, threshold, horizon, &buckets);
+                feeRate = block_policy_fee_estimator.estimateRawFee(conf_target, threshold, horizon, &buckets);
                 UniValue horizon_result(UniValue::VOBJ);
                 UniValue errors(UniValue::VARR);
                 UniValue passbucket(UniValue::VOBJ);

src/rpc/server_util.cpp

@@ -9,7 +9,8 @@
 #include <net_processing.h>
 #include <node/context.h>
 #include <node/miner.h>
-#include <policy/fees.h>
+#include <policy/fees/block_policy_estimator.h>
+#include <policy/fees/forecaster_man.h>
 #include <pow.h>
 #include <rpc/protocol.h>
 #include <rpc/request.h>
@@ -84,19 +85,20 @@ ChainstateManager& EnsureAnyChainman(const std::any& context)
     return EnsureChainman(EnsureAnyNodeContext(context));
 }
 
-CBlockPolicyEstimator& EnsureFeeEstimator(const NodeContext& node)
+FeeRateForecasterManager& EnsureForecasterMan(const NodeContext& node)
 {
-    if (!node.fee_estimator) {
+    if (!node.forecasterman) {
         throw JSONRPCError(RPC_INTERNAL_ERROR, "Fee estimation disabled");
     }
-    return *node.fee_estimator;
+    return *node.forecasterman.get();
 }
 
-CBlockPolicyEstimator& EnsureAnyFeeEstimator(const std::any& context)
+FeeRateForecasterManager& EnsureAnyForecasterMan(const std::any& context)
 {
-    return EnsureFeeEstimator(EnsureAnyNodeContext(context));
+    return EnsureForecasterMan(EnsureAnyNodeContext(context));
 }
 
+
 CConnman& EnsureConnman(const NodeContext& node)
 {
     if (!node.connman) {

src/rpc/server_util.h

@@ -12,7 +12,7 @@
 class AddrMan;
 class ArgsManager;
 class CBlockIndex;
-class CBlockPolicyEstimator;
+class FeeRateForecasterManager;
 class CConnman;
 class CTxMemPool;
 class ChainstateManager;
@@ -34,8 +34,8 @@ ArgsManager& EnsureArgsman(const node::NodeContext& node);
 ArgsManager& EnsureAnyArgsman(const std::any& context);
 ChainstateManager& EnsureChainman(const node::NodeContext& node);
 ChainstateManager& EnsureAnyChainman(const std::any& context);
-CBlockPolicyEstimator& EnsureFeeEstimator(const node::NodeContext& node);
+FeeRateForecasterManager& EnsureForecasterMan(const node::NodeContext& node);
-CBlockPolicyEstimator& EnsureAnyFeeEstimator(const std::any& context);
+FeeRateForecasterManager& EnsureAnyForecasterMan(const std::any& context);
 CConnman& EnsureConnman(const node::NodeContext& node);
 interfaces::Mining& EnsureMining(const node::NodeContext& node);
 PeerManager& EnsurePeerman(const node::NodeContext& node);

src/test/CMakeLists.txt

@@ -40,6 +40,8 @@ add_executable(test_bitcoin
   descriptor_tests.cpp
   disconnected_transactions.cpp
   feefrac_tests.cpp
+  feerounder_tests.cpp
+  forecaster_util_tests.cpp
   flatfile_tests.cpp
   fs_tests.cpp
   getarg_tests.cpp
@@ -52,6 +54,7 @@ add_executable(test_bitcoin
   key_tests.cpp
   logging_tests.cpp
   mempool_tests.cpp
+  mempoolforecaster_tests.cpp
   merkle_tests.cpp
   merkleblock_tests.cpp
   miner_tests.cpp
@@ -68,7 +71,6 @@ add_executable(test_bitcoin
   pcp_tests.cpp
   peerman_tests.cpp
   pmt_tests.cpp
-  policy_fee_tests.cpp
   policyestimator_tests.cpp
   pool_tests.cpp
   pow_tests.cpp

src/test/feerounder_tests.cpp

@@ -3,13 +3,13 @@
 // file COPYING or http://www.opensource.org/licenses/mit-license.php.
 
 #include <consensus/amount.h>
-#include <policy/fees.h>
+#include <policy/fees/block_policy_estimator.h>
 
 #include <boost/test/unit_test.hpp>
 
 #include <set>
 
-BOOST_AUTO_TEST_SUITE(policy_fee_tests)
+BOOST_AUTO_TEST_SUITE(fee_rounder_tests)
 
 BOOST_AUTO_TEST_CASE(FeeRounder)
 {

src/test/forecaster_util_tests.cpp

@@ -0,0 +1,65 @@
+// Copyright (c) 2024 The Bitcoin Core developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+
+#include <policy/fees/forecaster_util.h>
+#include <policy/policy.h>
+
+#include <boost/test/unit_test.hpp>
+#include <vector>
+
+BOOST_AUTO_TEST_SUITE(forecaster_util_tests)
+
+BOOST_AUTO_TEST_CASE(calculate_percentile_test)
+{
+    // Test that CalculatePercentiles returns empty when vector is empty
+    BOOST_CHECK(CalculatePercentiles({}, DEFAULT_BLOCK_MAX_WEIGHT).empty());
+
+    const int32_t package_size{10};
+    const int32_t individual_tx_vsize = static_cast<int32_t>(DEFAULT_BLOCK_MAX_WEIGHT / WITNESS_SCALE_FACTOR) / package_size;
+
+    // Define fee rate categories with corresponding fee rates in satoshis per kvB
+    const FeeFrac superHighFeerate{500 * individual_tx_vsize, individual_tx_vsize}; // Super High fee: 500 sat/kvB
+    const FeeFrac highFeerate{100 * individual_tx_vsize, individual_tx_vsize};      // High fee: 100 sat/kvB
+    const FeeFrac mediumFeerate{50 * individual_tx_vsize, individual_tx_vsize};     // Medium fee: 50 sat/kvB
+    const FeeFrac lowFeerate{10 * individual_tx_vsize, individual_tx_vsize};        // Low fee: 10 sat/kvB
+
+    std::vector<FeeFrac> package_feerates;
+    package_feerates.reserve(package_size);
+
+    // Populate the feerate histogram based on specified index ranges.
+    for (int i = 0; i < package_size; ++i) {
+        if (i < 3) {
+            package_feerates.emplace_back(superHighFeerate); // Super High fee rate for top 3
+        } else if (i < 5) {
+            package_feerates.emplace_back(highFeerate); // High fee rate for next 2
+        } else if (i < 8) {
+            package_feerates.emplace_back(mediumFeerate);                                          // Medium fee rate for next 3
+            BOOST_CHECK(CalculatePercentiles(package_feerates, DEFAULT_BLOCK_MAX_WEIGHT).empty()); // CalculatePercentiles should return empty until reaching the 95th percentile
+        } else {
+            package_feerates.emplace_back(lowFeerate); // Low fee rate for remaining 2
+        }
+    }
+
+    // Test percentile calculation on a complete histogram
+    {
+        const auto percentiles = CalculatePercentiles(package_feerates, DEFAULT_BLOCK_MAX_WEIGHT);
+        BOOST_CHECK(percentiles.p25 == superHighFeerate);
+        BOOST_CHECK(percentiles.p50 == highFeerate);
+        BOOST_CHECK(percentiles.p75 == mediumFeerate);
+        BOOST_CHECK(percentiles.p95 == lowFeerate);
+    }
+
+    // Test that CalculatePercentiles maintains monotonicity across all percentiles
+    {
+        package_feerates[7] = superHighFeerate; // Increase 8th index to a high fee rate
+        const auto percentiles = CalculatePercentiles(package_feerates, DEFAULT_BLOCK_MAX_WEIGHT);
+        BOOST_CHECK(percentiles.p25 == superHighFeerate);
+        BOOST_CHECK(percentiles.p50 == highFeerate);
+        BOOST_CHECK(percentiles.p75 == mediumFeerate); // Should still reflect the previous medium rate
+        BOOST_CHECK(percentiles.p95 == lowFeerate);
+    }
+}
+
+BOOST_AUTO_TEST_SUITE_END()

src/test/fuzz/fees.cpp

@@ -4,7 +4,7 @@
 
 #include <common/messages.h>
 #include <consensus/amount.h>
-#include <policy/fees.h>
+#include <policy/fees/block_policy_estimator.h>
 #include <test/fuzz/FuzzedDataProvider.h>
 #include <test/fuzz/fuzz.h>
 #include <test/fuzz/util.h>

src/test/fuzz/kitchen_sink.cpp

@@ -5,7 +5,7 @@
 #include <common/messages.h>
 #include <merkleblock.h>
 #include <node/types.h>
-#include <policy/fees.h>
+#include <policy/fees/block_policy_estimator.h>
 #include <rpc/util.h>
 #include <test/fuzz/FuzzedDataProvider.h>
 #include <test/fuzz/fuzz.h>

src/test/fuzz/policy_estimator.cpp

@@ -3,8 +3,8 @@
 // file COPYING or http://www.opensource.org/licenses/mit-license.php.
 
 #include <kernel/mempool_entry.h>
-#include <policy/fees.h>
+#include <policy/fees/block_policy_estimator.h>
-#include <policy/fees_args.h>
+#include <policy/fees/block_policy_estimator_args.h>
 #include <primitives/transaction.h>
 #include <streams.h>
 #include <test/fuzz/FuzzedDataProvider.h>

src/test/fuzz/policy_estimator_io.cpp

@@ -2,8 +2,8 @@
 // Distributed under the MIT software license, see the accompanying
 // file COPYING or http://www.opensource.org/licenses/mit-license.php.
 
-#include <policy/fees.h>
+#include <policy/fees/block_policy_estimator.h>
-#include <policy/fees_args.h>
+#include <policy/fees/block_policy_estimator_args.h>
 #include <streams.h>
 #include <test/fuzz/FuzzedDataProvider.h>
 #include <test/fuzz/fuzz.h>

src/test/mempoolforecaster_tests.cpp

@@ -0,0 +1,99 @@
+// Copyright (c) 2024 The Bitcoin Core developers
+// Distributed under the MIT software license. See the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#include <policy/fees/forecaster.h>
+#include <policy/fees/forecaster_util.h>
+#include <policy/fees/mempool_forecaster.h>
+#include <random.h>
+#include <test/util/txmempool.h>
+#include <txmempool.h>
+#include <uint256.h>
+#include <util/feefrac.h>
+#include <util/strencodings.h>
+#include <validation.h>
+
+
+#include <test/util/setup_common.h>
+
+#include <memory>
+#include <string>
+
+#include <boost/test/unit_test.hpp>
+
+BOOST_FIXTURE_TEST_SUITE(mempoolforecaster_tests, TestChain100Setup)
+
+static inline CTransactionRef make_random_tx()
+{
+    auto rng = FastRandomContext();
+    auto tx = CMutableTransaction();
+    tx.vin.resize(1);
+    tx.vout.resize(1);
+    tx.vin[0].prevout.hash = Txid::FromUint256(rng.rand256());
+    tx.vin[0].prevout.n = 0;
+    tx.vin[0].scriptSig << OP_TRUE;
+    tx.vout[0].scriptPubKey = CScript() << OP_TRUE;
+    tx.vout[0].nValue = COIN;
+    return MakeTransactionRef(tx);
+}
+
+BOOST_AUTO_TEST_CASE(MempoolEstimator)
+{
+    auto mempool_fee_estimator = std::make_unique<MemPoolForecaster>(m_node.mempool.get(), &(m_node.chainman->ActiveChainstate()));
+    ConfirmationTarget conf_target = {MEMPOOL_FORECAST_MAX_TARGET + 1, ConfirmationTargetType::BLOCKS};
+    LOCK2(cs_main, m_node.mempool->cs);
+    {
+        // Test when targetBlocks > MEMPOOL_FORECAST_MAX_TARGET
+        const auto fee_estimate = mempool_fee_estimator->EstimateFee(conf_target);
+        BOOST_CHECK(fee_estimate.Empty());
+        BOOST_CHECK(*fee_estimate.GetError() == strprintf("Confirmation target %s exceeds the maximum limit of %s. mempool conditions might change, "
+                                                          "making forecasts above %s block may be unreliable",
+                                                          MEMPOOL_FORECAST_MAX_TARGET + 1, MEMPOOL_FORECAST_MAX_TARGET, MEMPOOL_FORECAST_MAX_TARGET));
+    }
+
+    BOOST_CHECK(m_node.mempool->GetTotalTxSize() == 0);
+    TestMemPoolEntryHelper entry;
+
+    const CAmount low_fee{CENT / 3000};
+    const CAmount med_fee{CENT / 100};
+    const CAmount high_fee{CENT / 10};
+
+    conf_target.value = MEMPOOL_FORECAST_MAX_TARGET;
+    // Test when there are not enough mempool transactions to get an accurate estimate
+    {
+        // Add transactions with high_fee fee until mempool transactions weight is more than 25th percent of DEFAULT_BLOCK_MAX_WEIGHT
+        while (static_cast<int>(m_node.mempool->GetTotalTxSize() * WITNESS_SCALE_FACTOR) <= static_cast<int>(0.25 * DEFAULT_BLOCK_MAX_WEIGHT)) {
+            AddToMempool(*m_node.mempool, entry.Fee(high_fee).FromTx(make_random_tx()));
+        }
+        const auto fee_estimate = mempool_fee_estimator->EstimateFee(conf_target);
+        BOOST_CHECK(fee_estimate.Empty());
+        BOOST_CHECK(*fee_estimate.GetError() == "Forecaster unable to provide an estimate due to insufficient data");
+    }
+
+    {
+        // Add transactions with med_fee fee until mempool transactions weight is more than 50th percent of DEFAULT_BLOCK_MAX_WEIGHT
+        while (static_cast<int>(m_node.mempool->GetTotalTxSize() * WITNESS_SCALE_FACTOR) <= static_cast<int>(0.5 * DEFAULT_BLOCK_MAX_WEIGHT)) {
+            AddToMempool(*m_node.mempool, entry.Fee(med_fee).FromTx(make_random_tx()));
+        }
+        const auto fee_estimate = mempool_fee_estimator->EstimateFee(conf_target);
+        BOOST_CHECK(fee_estimate.Empty());
+        BOOST_CHECK(*fee_estimate.GetError() == "Forecaster unable to provide an estimate due to insufficient data");
+    }
+
+    // Mempool transactions are enough to provide feerate estimate
+    {
+        // Add low_fee transactions until mempool transactions weight is more than 95th percent of DEFAULT_BLOCK_MAX_WEIGHT
+        while (static_cast<int>(m_node.mempool->GetTotalTxSize() * WITNESS_SCALE_FACTOR) <= static_cast<int>(0.95 * DEFAULT_BLOCK_MAX_WEIGHT)) {
+            const auto txref = make_random_tx();
+            AddToMempool(*m_node.mempool, entry.Fee(low_fee).FromTx(make_random_tx()));
+        }
+
+        const auto fee_estimate = mempool_fee_estimator->EstimateFee(conf_target);
+        BOOST_CHECK(!fee_estimate.Empty());
+        const auto tx_vsize = entry.FromTx(make_random_tx()).GetTxSize();
+        BOOST_CHECK(fee_estimate.GetResponse().low_priority == FeeFrac(low_fee, tx_vsize));
+        BOOST_CHECK(fee_estimate.GetResponse().high_priority == FeeFrac(med_fee, tx_vsize));
+    }
+}
+
+BOOST_AUTO_TEST_SUITE_END()

src/test/policyestimator_tests.cpp

@@ -2,8 +2,8 @@
 // Distributed under the MIT software license, see the accompanying
 // file COPYING or http://www.opensource.org/licenses/mit-license.php.
 
-#include <policy/fees.h>
+#include <policy/fees/block_policy_estimator.h>
-#include <policy/fees_args.h>
+#include <policy/fees/block_policy_estimator_args.h>
 #include <policy/policy.h>
 #include <test/util/txmempool.h>
 #include <txmempool.h>

src/test/util/setup_common.cpp

@@ -28,7 +28,7 @@
 #include <node/peerman_args.h>
 #include <node/warnings.h>
 #include <noui.h>
-#include <policy/fees.h>
+#include <policy/fees/block_policy_estimator.h>
 #include <pow.h>
 #include <random.h>
 #include <rpc/blockchain.h>
@@ -275,7 +275,7 @@ ChainTestingSetup::~ChainTestingSetup()
     m_node.netgroupman.reset();
     m_node.args = nullptr;
     m_node.mempool.reset();
-    Assert(!m_node.fee_estimator); // Each test must create a local object, if they wish to use the fee_estimator
+    Assert(!m_node.forecasterman); // Each test must create a local object, if they wish to use the forecasterman
     m_node.chainman.reset();
     m_node.validation_signals.reset();
     m_node.scheduler.reset();

src/wallet/coincontrol.h

@@ -7,7 +7,7 @@
 
 #include <outputtype.h>
 #include <policy/feerate.h>
-#include <policy/fees.h>
+#include <policy/fees/block_policy_estimator.h>
 #include <primitives/transaction.h>
 #include <script/keyorigin.h>
 #include <script/signingprovider.h>

src/wallet/feebumper.cpp

@@ -6,7 +6,7 @@
 #include <consensus/validation.h>
 #include <interfaces/chain.h>
 #include <node/types.h>
-#include <policy/fees.h>
+#include <policy/fees/block_policy_estimator.h>
 #include <policy/policy.h>
 #include <util/moneystr.h>
 #include <util/rbf.h>

src/wallet/interfaces.cpp

@@ -9,7 +9,7 @@
 #include <interfaces/chain.h>
 #include <interfaces/handler.h>
 #include <node/types.h>
-#include <policy/fees.h>
+#include <policy/fees/block_policy_estimator.h>
 #include <primitives/transaction.h>
 #include <rpc/server.h>
 #include <scheduler.h>

src/wallet/spend.h

@@ -6,7 +6,7 @@
 #define BITCOIN_WALLET_SPEND_H
 
 #include <consensus/amount.h>
-#include <policy/fees.h> // for FeeCalculation
+#include <policy/fees/block_policy_estimator.h> // for FeeCalculation
 #include <util/result.h>
 #include <wallet/coinselection.h>
 #include <wallet/transaction.h>

src/wallet/test/spend_tests.cpp

@@ -3,7 +3,7 @@
 // file COPYING or http://www.opensource.org/licenses/mit-license.php.
 
 #include <consensus/amount.h>
-#include <policy/fees.h>
+#include <policy/fees/block_policy_estimator.h>
 #include <script/solver.h>
 #include <validation.h>
 #include <wallet/coincontrol.h>