// Copyright (c) 2009-2010 Satoshi Nakamoto // Copyright (c) 2009-2016 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_POLICYESTIMATOR_H #define BITCOIN_POLICYESTIMATOR_H #include "amount.h" #include "uint256.h" #include "random.h" #include "sync.h" #include #include #include class CAutoFile; class CFeeRate; class CTxMemPoolEntry; class CTxMemPool; /** \class CBlockPolicyEstimator * The BlockPolicyEstimator is used for estimating the feerate needed * for a transaction to be included in a block within a certain number of * blocks. * * At a high level the algorithm works by grouping transactions into buckets * based on having similar feerates and then tracking how long it * takes transactions in the various buckets to be mined. It operates under * the assumption that in general transactions of higher feerate will be * included in blocks before transactions of lower feerate. So for * example if you wanted to know what feerate you should put on a transaction to * be included in a block within the next 5 blocks, you would start by looking * at the bucket with the highest feerate transactions and verifying that a * sufficiently high percentage of them were confirmed within 5 blocks and * then you would look at the next highest feerate bucket, and so on, stopping at * the last bucket to pass the test. The average feerate of transactions in this * bucket will give you an indication of the lowest feerate you can put on a * transaction and still have a sufficiently high chance of being confirmed * within your desired 5 blocks. * * Here is a brief description of the implementation: * When a transaction enters the mempool, we * track the height of the block chain at entry. Whenever a block comes in, * we count the number of transactions in each bucket and the total amount of feerate * paid in each bucket. Then we calculate how many blocks Y it took each * transaction to be mined and we track an array of counters in each bucket * for how long it to took transactions to get confirmed from 1 to a max of 25 * and we increment all the counters from Y up to 25. This is because for any * number Z>=Y the transaction was successfully mined within Z blocks. We * want to save a history of this information, so at any time we have a * counter of the total number of transactions that happened in a given feerate * bucket and the total number that were confirmed in each number 1-25 blocks * or less for any bucket. We save this history by keeping an exponentially * decaying moving average of each one of these stats. Furthermore we also * keep track of the number unmined (in mempool) transactions in each bucket * and for how many blocks they have been outstanding and use that to increase * the number of transactions we've seen in that feerate bucket when calculating * an estimate for any number of confirmations below the number of blocks * they've been outstanding. */ /** * We will instantiate an instance of this class to track transactions that were * included in a block. We will lump transactions into a bucket according to their * approximate feerate and then track how long it took for those txs to be included in a block * * The tracking of unconfirmed (mempool) transactions is completely independent of the * historical tracking of transactions that have been confirmed in a block. */ class TxConfirmStats { private: //Define the buckets we will group transactions into std::vector buckets; // The upper-bound of the range for the bucket (inclusive) std::map bucketMap; // Map of bucket upper-bound to index into all vectors by bucket // For each bucket X: // Count the total # of txs in each bucket // Track the historical moving average of this total over blocks std::vector txCtAvg; // and calculate the total for the current block to update the moving average std::vector curBlockTxCt; // Count the total # of txs confirmed within Y blocks in each bucket // Track the historical moving average of theses totals over blocks std::vector > confAvg; // confAvg[Y][X] // and calculate the totals for the current block to update the moving averages std::vector > curBlockConf; // curBlockConf[Y][X] // Sum the total feerate of all tx's in each bucket // Track the historical moving average of this total over blocks std::vector avg; // and calculate the total for the current block to update the moving average std::vector curBlockVal; // Combine the conf counts with tx counts to calculate the confirmation % for each Y,X // Combine the total value with the tx counts to calculate the avg feerate per bucket double decay; // Mempool counts of outstanding transactions // For each bucket X, track the number of transactions in the mempool // that are unconfirmed for each possible confirmation value Y std::vector > unconfTxs; //unconfTxs[Y][X] // transactions still unconfirmed after MAX_CONFIRMS for each bucket std::vector oldUnconfTxs; public: /** * Create new TxConfirmStats. This is called by BlockPolicyEstimator's * constructor with default values. * @param defaultBuckets contains the upper limits for the bucket boundaries * @param maxConfirms max number of confirms to track * @param decay how much to decay the historical moving average per block */ TxConfirmStats(const std::vector& defaultBuckets, unsigned int maxConfirms, double decay); /** Clear the state of the curBlock variables to start counting for the new block */ void ClearCurrent(unsigned int nBlockHeight); /** * Record a new transaction data point in the current block stats * @param blocksToConfirm the number of blocks it took this transaction to confirm * @param val the feerate of the transaction * @warning blocksToConfirm is 1-based and has to be >= 1 */ void Record(int blocksToConfirm, double val); /** Record a new transaction entering the mempool*/ unsigned int NewTx(unsigned int nBlockHeight, double val); /** Remove a transaction from mempool tracking stats*/ void removeTx(unsigned int entryHeight, unsigned int nBestSeenHeight, unsigned int bucketIndex); /** Update our estimates by decaying our historical moving average and updating with the data gathered from the current block */ void UpdateMovingAverages(); /** * Calculate a feerate estimate. Find the lowest value bucket (or range of buckets * to make sure we have enough data points) whose transactions still have sufficient likelihood * of being confirmed within the target number of confirmations * @param confTarget target number of confirmations * @param sufficientTxVal required average number of transactions per block in a bucket range * @param minSuccess the success probability we require * @param requireGreater return the lowest feerate such that all higher values pass minSuccess OR * return the highest feerate such that all lower values fail minSuccess * @param nBlockHeight the current block height */ double EstimateMedianVal(int confTarget, double sufficientTxVal, double minSuccess, bool requireGreater, unsigned int nBlockHeight) const; /** Return the max number of confirms we're tracking */ unsigned int GetMaxConfirms() const { return confAvg.size(); } /** Write state of estimation data to a file*/ void Write(CAutoFile& fileout) const; /** * Read saved state of estimation data from a file and replace all internal data structures and * variables with this state. */ void Read(CAutoFile& filein); }; /** Track confirm delays up to 25 blocks, can't estimate beyond that */ static const unsigned int MAX_BLOCK_CONFIRMS = 25; /** Decay of .998 is a half-life of 346 blocks or about 2.4 days */ static const double DEFAULT_DECAY = .998; /** Require greater than 95% of X feerate transactions to be confirmed within Y blocks for X to be big enough */ static const double MIN_SUCCESS_PCT = .95; /** Require an avg of 1 tx in the combined feerate bucket per block to have stat significance */ static const double SUFFICIENT_FEETXS = 1; // Minimum and Maximum values for tracking feerates // The MIN_BUCKET_FEERATE should just be set to the lowest reasonable feerate we // might ever want to track. Historically this has been 1000 since it was // inheriting DEFAULT_MIN_RELAY_TX_FEE and changing it is disruptive as it // invalidates old estimates files. So leave it at 1000 unless it becomes // necessary to lower it, and then lower it substantially. static constexpr double MIN_BUCKET_FEERATE = 1000; static const double MAX_BUCKET_FEERATE = 1e7; static const double INF_FEERATE = MAX_MONEY; // We have to lump transactions into buckets based on feerate, but we want to be able // to give accurate estimates over a large range of potential feerates // Therefore it makes sense to exponentially space the buckets /** Spacing of FeeRate buckets */ static const double FEE_SPACING = 1.1; /** * We want to be able to estimate feerates that are needed on tx's to be included in * 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: /** Create new BlockPolicyEstimator and initialize stats tracking classes with default values */ CBlockPolicyEstimator(); ~CBlockPolicyEstimator(); /** Process all the transactions that have been included in a block */ void processBlock(unsigned int nBlockHeight, std::vector& entries); /** Process a transaction accepted to the mempool*/ void processTransaction(const CTxMemPoolEntry& entry, bool validFeeEstimate); /** Remove a transaction from the mempool tracking stats*/ bool removeTx(uint256 hash); /** Return a feerate estimate */ CFeeRate estimateFee(int confTarget) const; /** Estimate feerate needed to get be included in a block within * confTarget blocks. If no answer can be given at confTarget, return an * estimate at the lowest target where one can be given. */ CFeeRate estimateSmartFee(int confTarget, int *answerFoundAtTarget, const CTxMemPool& pool) const; /** Write estimation data to a file */ bool Write(CAutoFile& fileout) const; /** Read estimation data from a file */ bool Read(CAutoFile& filein); private: CFeeRate minTrackedFee; //!< Passed to constructor to avoid dependency on main unsigned int nBestSeenHeight; struct TxStatsInfo { unsigned int blockHeight; unsigned int bucketIndex; TxStatsInfo() : blockHeight(0), bucketIndex(0) {} }; // map of txids to information about that transaction std::map mapMemPoolTxs; /** Classes to track historical data on transaction confirmations */ TxConfirmStats* feeStats; unsigned int trackedTxs; unsigned int untrackedTxs; mutable CCriticalSection cs_feeEstimator; /** Process a transaction confirmed in a block*/ bool processBlockTx(unsigned int nBlockHeight, const CTxMemPoolEntry* entry); }; class FeeFilterRounder { public: /** Create new FeeFilterRounder */ FeeFilterRounder(const CFeeRate& minIncrementalFee); /** Quantize a minimum fee for privacy purpose before broadcast **/ CAmount round(CAmount currentMinFee); private: std::set feeset; FastRandomContext insecure_rand; }; #endif /*BITCOIN_POLICYESTIMATOR_H */