@ -22,51 +22,6 @@ class CTxMemPoolEntry;
class CTxMemPool ;
class TxConfirmStats ;
/** \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 . All further calculations are conducted only on this set of " seen "
* transactions . 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 . We convert
* from a number of blocks to a number of periods Y ' each encompassing " scale "
* blocks . This is tracked in 3 different data sets each up to a maximum
* number of periods . Within each data set we have an array of counters in each
* feerate bucket and we increment all the counters from Y ' up to max periods
* representing that a tx was successfully confirmed in less than or equal to
* that many periods . 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 of the
* periods or less for any bucket . We save this history by keeping an
* exponentially decaying moving average of each one of these stats . This is
* done for a different decay in each of the 3 data sets to keep relevant data
* from different time horizons . Furthermore we also keep track of the number
* unmined ( in mempool or left mempool without being included in a block )
* transactions in each bucket and for how many blocks they have been
* outstanding and use both of these numbers 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 .
*/
/* Identifier for each of the 3 different TxConfirmStats which will track
* history over different time horizons . */
enum class FeeEstimateHorizon {
@ -130,7 +85,50 @@ struct FeeCalculation
int returnedTarget = 0 ;
} ;
/**
/** \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 . All further calculations are conducted only on this set of " seen "
* transactions . 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 . We convert
* from a number of blocks to a number of periods Y ' each encompassing " scale "
* blocks . This is tracked in 3 different data sets each up to a maximum
* number of periods . Within each data set we have an array of counters in each
* feerate bucket and we increment all the counters from Y ' up to max periods
* representing that a tx was successfully confirmed in less than or equal to
* that many periods . 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 of the
* periods or less for any bucket . We save this history by keeping an
* exponentially decaying moving average of each one of these stats . This is
* done for a different decay in each of the 3 data sets to keep relevant data
* from different time horizons . Furthermore we also keep track of the number
* unmined ( in mempool or left mempool without being included in a block )
* transactions in each bucket and for how many blocks they have been
* outstanding and use both of these numbers 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 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