瞭解了區塊和交易的資料結構，接下來就是介於這兩者之間的一個重要的資料結構：交易池。
當比特幣網路把某個時刻產生的交易廣播到網路時，礦工接收到交易後並不是立即打包到備選區塊。而是將接收到的交易放到類似緩衝區的一個交易池裡，然後會根據一定的優先順序來選擇交易打包，以此來保障自己能獲得儘可能多的交易費。
所以瞭解交易池的資料結構，對理解礦工打包交易會有很大的裨益。
找啊找啊找交易池
首先我猜測有關交易池的類可能叫transactionPool，於是我試著全域性搜這個詞：
於是，我擴大搜尋範圍，搜尋pool。搜到的結果很多，我大概地往下翻，試圖尋找是交易池的那個。找到很多處mempool，於是我點進去試著搜尋mempool，找到了txmempool.h這個標頭檔案，交易記憶體池，應該就是這個了。
原始碼初窺
- 程式碼路徑: bitcoin/src/txmempool.h
LockPoints
/** Fake height value used in Coin to signify they are only in the memory pool (since 0.8) */
//一個"假"的高度值，用來標識它們只存在於交易池中
static const uint32_t MEMPOOL_HEIGHT = 0x7FFFFFFF;
//交易鎖定點,交易最後的區塊高度和打包時間
struct LockPoints
{
// Will be set to the blockchain height and median time past
// values that would be necessary to satisfy all relative locktime
// constraints (BIP68) of this tx given our view of block chain history
/**
* 將設定為區塊鏈高度和中值時間過去值,
* 這些值對於滿足tx相對時間鎖是至關重要的(BIP68)
*
*/
int height;
int64_t time;
// As long as the current chain descends from the highest height block
// containing one of the inputs used in the calculation, then the cached
// values are still valid even after a reorg.
/**
* 只要當前鏈包含計算中使用的某個輸入的最高快高度，
* 則即使在鏈重新構建後快取的值依然有效
*/
CBlockIndex* maxInputBlock;
LockPoints() : height(0), time(0), maxInputBlock(nullptr) { }
};
複製程式碼CTxMemPoolEntry
class CTxMemPool;
/** \class CTxMemPoolEntry
*
* CTxMemPoolEntry stores data about the corresponding transaction, as well
* as data about all in-mempool transactions that depend on the transaction
* ("descendant" transactions).
*
* When a new entry is added to the mempool, we update the descendant state
* (nCountWithDescendants, nSizeWithDescendants, and nModFeesWithDescendants) for
* all ancestors of the newly added transaction.
*
**CTxMemPoolEntry 儲存相應的交易
* 以及該交易對應的所有子孫交易
*
* 當一個新的CTxMemPoolEntry被新增到交易池，我們會更新新新增交易的所有子孫交易的狀態
* (包括子孫交易數量，大小，和交易費用）和祖父交易狀態
*/
//交易池基本構成元素
class CTxMemPoolEntry
{
private:
CTransactionRef tx; //交易引用
CAmount nFee; //交易費用 //!< Cached to avoid expensive parent-transaction lookups
size_t nTxWeight; // //!< ... and avoid recomputing tx weight (also used for GetTxSize())
size_t nUsageSize; //大小 //!< ... and total memory usage
int64_t nTime; //交易時間戳 //!< Local time when entering the mempool
unsigned int entryHeight; //區塊高度 //!< Chain height when entering the mempool
bool spendsCoinbase; //上個交易是否是創幣交易 //!< keep track of transactions that spend a coinbase
int64_t sigOpCost; //？？？ !< Total sigop cost
int64_t feeDelta; //交易優先順序的一個標量 //!< Used for determining the priority of the transaction for mining in a block
LockPoints lockPoints; //鎖定點，交易最後的區塊高度和打包時間 //!< Track the height and time at which tx was final
// Information about descendants of this transaction that are in the
// mempool; if we remove this transaction we must remove all of these
// descendants as well.
/*
** 子孫交易資訊
* 如果我們移除一個交易，我們也必須同時移除它所有的子孫交易
*/
uint64_t nCountWithDescendants; //子孫交易數量 //!< number of descendant transactions
uint64_t nSizeWithDescendants; //大小 //!< ... and size
CAmount nModFeesWithDescendants; //費用總和，包括當前交易 //!< ... and total fees (all including us)
// Analogous statistics for ancestor transactions
//祖先交易資訊
uint64_t nCountWithAncestors; //祖先交易數量
uint64_t nSizeWithAncestors; //大小
CAmount nModFeesWithAncestors; //費用總和
int64_t nSigOpCostWithAncestors; //？？？
public:
CTxMemPoolEntry(const CTransactionRef& _tx, const CAmount& _nFee,
int64_t _nTime, unsigned int _entryHeight,
bool spendsCoinbase,
int64_t nSigOpsCost, LockPoints lp);
const CTransaction& GetTx() const { return *this->tx; }
CTransactionRef GetSharedTx() const { return this->tx; }
const CAmount& GetFee() const { return nFee; }
size_t GetTxSize() const;
size_t GetTxWeight() const { return nTxWeight; }
int64_t GetTime() const { return nTime; }
unsigned int GetHeight() const { return entryHeight; }
int64_t GetSigOpCost() const { return sigOpCost; }
int64_t GetModifiedFee() const { return nFee + feeDelta; }
size_t DynamicMemoryUsage() const { return nUsageSize; }
const LockPoints& GetLockPoints() const { return lockPoints; }
// Adjusts the descendant state.
// 更新子孫交易狀態
void UpdateDescendantState(int64_t modifySize, CAmount modifyFee, int64_t modifyCount);
// Adjusts the ancestor state
// 更新祖先交易狀態
void UpdateAncestorState(int64_t modifySize, CAmount modifyFee, int64_t modifyCount, int64_t modifySigOps);
// Updates the fee delta used for mining priority score, and the
// modified fees with descendants.
// 更新交易優先順序
void UpdateFeeDelta(int64_t feeDelta);
// Update the LockPoints after a reorg
// 更新鎖定點
void UpdateLockPoints(const LockPoints& lp);
//獲取子孫交易資訊
uint64_t GetCountWithDescendants() const { return nCountWithDescendants; }
uint64_t GetSizeWithDescendants() const { return nSizeWithDescendants; }
CAmount GetModFeesWithDescendants() const { return nModFeesWithDescendants; }
bool GetSpendsCoinbase() const { return spendsCoinbase; }
//獲取祖先交易資訊
uint64_t GetCountWithAncestors() const { return nCountWithAncestors; }
uint64_t GetSizeWithAncestors() const { return nSizeWithAncestors; }
CAmount GetModFeesWithAncestors() const { return nModFeesWithAncestors; }
int64_t GetSigOpCostWithAncestors() const { return nSigOpCostWithAncestors; }
mutable size_t vTxHashesIdx; //交易池雜湊的下標 //!< Index in mempool's vTxHashes
};
複製程式碼CTxMemPoolEntry幾種排序方法
/** \class CompareTxMemPoolEntryByDescendantScore
*
* Sort an entry by max(score/size of entry's tx, score/size with all descendants).
*
** 按score/size原則對CTxMemPoolEntry排序
*/
class CompareTxMemPoolEntryByDescendantScore
{
public:
bool operator()(const CTxMemPoolEntry& a, const CTxMemPoolEntry& b) const
{
double a_mod_fee, a_size, b_mod_fee, b_size;
GetModFeeAndSize(a, a_mod_fee, a_size);
GetModFeeAndSize(b, b_mod_fee, b_size);
// Avoid division by rewriting (a/b > c/d) as (a*d > c*b).
double f1 = a_mod_fee * b_size;
double f2 = a_size * b_mod_fee;
if (f1 == f2) {
return a.GetTime() >= b.GetTime();
}
return f1 < f2;
}
// Return the fee/size we're using for sorting this entry.
void GetModFeeAndSize(const CTxMemPoolEntry &a, double &mod_fee, double &size) const
{
// Compare feerate with descendants to feerate of the transaction, and
// return the fee/size for the max.
double f1 = (double)a.GetModifiedFee() * a.GetSizeWithDescendants();
double f2 = (double)a.GetModFeesWithDescendants() * a.GetTxSize();
if (f2 > f1) {
mod_fee = a.GetModFeesWithDescendants();
size = a.GetSizeWithDescendants();
} else {
mod_fee = a.GetModifiedFee();
size = a.GetTxSize();
}
}
};
/** \class CompareTxMemPoolEntryByScore
*
* Sort by score of entry ((fee+delta)/size) in descending order
**
* 按(fee+delta)/size原則對CTxMemPoolEntry排序
*/
class CompareTxMemPoolEntryByScore
{
public:
bool operator()(const CTxMemPoolEntry& a, const CTxMemPoolEntry& b) const
{
double f1 = (double)a.GetModifiedFee() * b.GetTxSize();
double f2 = (double)b.GetModifiedFee() * a.GetTxSize();
if (f1 == f2) {
return b.GetTx().GetHash() < a.GetTx().GetHash();
}
return f1 > f2;
}
};
//按時間CTxMemPoolEntry對排序
class CompareTxMemPoolEntryByEntryTime
{
public:
bool operator()(const CTxMemPoolEntry& a, const CTxMemPoolEntry& b) const
{
return a.GetTime() < b.GetTime();
}
};
/** \class CompareTxMemPoolEntryByAncestorScore
*
* Sort an entry by min(score/size of entry's tx, score/size with all ancestors).
*/
class CompareTxMemPoolEntryByAncestorFee
{
public:
template<typename T>
bool operator()(const T& a, const T& b) const
{
double a_mod_fee, a_size, b_mod_fee, b_size;
GetModFeeAndSize(a, a_mod_fee, a_size);
GetModFeeAndSize(b, b_mod_fee, b_size);
// Avoid division by rewriting (a/b > c/d) as (a*d > c*b).
double f1 = a_mod_fee * b_size;
double f2 = a_size * b_mod_fee;
if (f1 == f2) {
return a.GetTx().GetHash() < b.GetTx().GetHash();
}
return f1 > f2;
}
// Return the fee/size we're using for sorting this entry.
template <typename T>
void GetModFeeAndSize(const T &a, double &mod_fee, double &size) const
{
// Compare feerate with ancestors to feerate of the transaction, and
// return the fee/size for the min.
double f1 = (double)a.GetModifiedFee() * a.GetSizeWithAncestors();
double f2 = (double)a.GetModFeesWithAncestors() * a.GetTxSize();
if (f1 > f2) {
mod_fee = a.GetModFeesWithAncestors();
size = a.GetSizeWithAncestors();
} else {
mod_fee = a.GetModifiedFee();
size = a.GetTxSize();
}
}
};
複製程式碼TxMempoolInfo
/**
* Information about a mempool transaction.
* 交易進入記憶體池的資訊
*/
struct TxMempoolInfo
{
/** The transaction itself */
CTransactionRef tx; //交易引用
/** Time the transaction entered the mempool. */
int64_t nTime; //交易進入記憶體池時間
/** Feerate of the transaction. */
CFeeRate feeRate; //交易費率
/** The fee delta. */
int64_t nFeeDelta; //交易優先順序
};
複製程式碼###MemPoolRemovalReason
/** Reason why a transaction was removed from the mempool,
* this is passed to the notification signal.
*
* 交易被移出記憶體池的原因
*/
enum class MemPoolRemovalReason {
UNKNOWN = 0, //未知原因 //! Manually removed or unknown reason
EXPIRY, //過期 //! Expired from mempool
SIZELIMIT, //大小限制 //! Removed in size limiting
REORG, //被重組 //! Removed for reorganization
BLOCK, //因為區塊 //! Removed for block
CONFLICT, //區塊內交易衝突//! Removed for conflict with in-block transaction
REPLACED //被替代 //! Removed for replacement
};
複製程式碼CTxMemPool
/**
* CTxMemPool stores valid-according-to-the-current-best-chain transactions
* that may be included in the next block.
*
* CTxMemPool 儲存當前主鏈所有的交易。這些交易有可能被加入到下一個有效區塊中
*
* Transactions are added when they are seen on the network (or created by the
* local node), but not all transactions seen are added to the pool. For
* example, the following new transactions will not be added to the mempool:
* - a transaction which doesn't meet the minimum fee requirements.
* - a new transaction that double-spends an input of a transaction already in
* the pool where the new transaction does not meet the Replace-By-Fee
* requirements as defined in BIP 125.
* - a non-standard transaction.
*
**當交易在比特幣網路上廣播時會被加入到交易池。
* 比如以下新的交易將不會被加入到交易池中：
* - 1.沒有滿足最低交易費的交易
* - 2."雙花"交易
* - 3.一個非標準交易
*
* CTxMemPool::mapTx, and CTxMemPoolEntry bookkeeping:
*
* mapTx is a boost::multi_index that sorts the mempool on 4 criteria:
* - transaction hash //交易hash
* - //交易費率(包括所有子孫交易)
* - feerate [we use max(feerate of tx, feerate of tx with all descendants)]
* - time in mempool //加入交易池的時間
*
* Note: the term "descendant" refers to in-mempool transactions that depend on
* this one, while "ancestor" refers to in-mempool transactions that a given
* transaction depends on.
*
* In order for the feerate sort to remain correct, we must update transactions
* in the mempool when new descendants arrive. To facilitate this, we track
* the set of in-mempool direct parents and direct children in mapLinks. Within
* each CTxMemPoolEntry, we track the size and fees of all descendants.
*
** 為了保障交易費的正確性，當新交易被加入到交易池時，我們必須更新該交易的所有祖先交易和子孫交易。
*
* Usually when a new transaction is added to the mempool, it has no in-mempool
* children (because any such children would be an orphan). So in
* addUnchecked(), we:
* - update a new entry's setMemPoolParents to include all in-mempool parents
* - update the new entry's direct parents to include the new tx as a child
* - update all ancestors of the transaction to include the new tx's size/fee
*
* When a transaction is removed from the mempool, we must:
* - update all in-mempool parents to not track the tx in setMemPoolChildren
* - update all ancestors to not include the tx's size/fees in descendant state
* - update all in-mempool children to not include it as a parent
*
* These happen in UpdateForRemoveFromMempool(). (Note that when removing a
* transaction along with its descendants, we must calculate that set of
* transactions to be removed before doing the removal, or else the mempool can
* be in an inconsistent state where it's impossible to walk the ancestors of
* a transaction.)
*
* In the event of a reorg, the assumption that a newly added tx has no
* in-mempool children is false. In particular, the mempool is in an
* inconsistent state while new transactions are being added, because there may
* be descendant transactions of a tx coming from a disconnected block that are
* unreachable from just looking at transactions in the mempool (the linking
* transactions may also be in the disconnected block, waiting to be added).
* Because of this, there's not much benefit in trying to search for in-mempool
* children in addUnchecked(). Instead, in the special case of transactions
* being added from a disconnected block, we require the caller to clean up the
* state, to account for in-mempool, out-of-block descendants for all the
* in-block transactions by calling UpdateTransactionsFromBlock(). Note that
* until this is called, the mempool state is not consistent, and in particular
* mapLinks may not be correct (and therefore functions like
* CalculateMemPoolAncestors() and CalculateDescendants() that rely
* on them to walk the mempool are not generally safe to use).
*
* Computational limits:
*
* Updating all in-mempool ancestors of a newly added transaction can be slow,
* if no bound exists on how many in-mempool ancestors there may be.
* CalculateMemPoolAncestors() takes configurable limits that are designed to
* prevent these calculations from being too CPU intensive.
*
*/
class CTxMemPool
{
private:
uint32_t nCheckFrequency; //2^32時間檢查的次數 //!< Value n means that n times in 2^32 we check.
unsigned int nTransactionsUpdated; //!< Used by getblocktemplate to trigger CreateNewBlock() invocation
CBlockPolicyEstimator* minerPolicyEstimator;
uint64_t totalTxSize; //交易池虛擬大小，不包括見證資料 //!< sum of all mempool tx's virtual sizes. Differs from serialized tx size since witness data is discounted. Defined in BIP 141.
uint64_t cachedInnerUsage; //map使用的動態記憶體大小 //!< sum of dynamic memory usage of all the map elements (NOT the maps themselves)
mutable int64_t lastRollingFeeUpdate;
mutable bool blockSinceLastRollingFeeBump;
mutable double rollingMinimumFeeRate; //進入交易池需要滿足的最小費用 //!< minimum fee to get into the pool, decreases exponentially
void trackPackageRemoved(const CFeeRate& rate);
public:
static const int ROLLING_FEE_HALFLIFE = 60 * 60 * 12; // public only for testing
typedef boost::multi_index_container<
CTxMemPoolEntry,
boost::multi_index::indexed_by<
// sorted by txid 根據交易雜湊排序
boost::multi_index::hashed_unique<mempoolentry_txid, SaltedTxidHasher>,
// sorted by fee rate 交易費
boost::multi_index::ordered_non_unique<
boost::multi_index::tag<descendant_score>,
boost::multi_index::identity<CTxMemPoolEntry>,
CompareTxMemPoolEntryByDescendantScore
>,
// sorted by entry time 進入交易池的時間
boost::multi_index::ordered_non_unique<
boost::multi_index::tag<entry_time>,
boost::multi_index::identity<CTxMemPoolEntry>,
CompareTxMemPoolEntryByEntryTime
>,
// sorted by fee rate with ancestors 祖父交易交易費
boost::multi_index::ordered_non_unique<
boost::multi_index::tag<ancestor_score>,
boost::multi_index::identity<CTxMemPoolEntry>,
CompareTxMemPoolEntryByAncestorFee
>
>
> indexed_transaction_set;
mutable CCriticalSection cs;
indexed_transaction_set mapTx;
typedef indexed_transaction_set::nth_index<0>::type::iterator txiter;
std::vector<std::pair<uint256, txiter> > vTxHashes; //見證資料的雜湊 //!< All tx witness hashes/entries in mapTx, in random order
struct CompareIteratorByHash {
bool operator()(const txiter &a, const txiter &b) const {
return a->GetTx().GetHash() < b->GetTx().GetHash();
}
};
typedef std::set<txiter, CompareIteratorByHash> setEntries;
const setEntries & GetMemPoolParents(txiter entry) const;
const setEntries & GetMemPoolChildren(txiter entry) const;
private:
typedef std::map<txiter, setEntries, CompareIteratorByHash> cacheMap;
struct TxLinks {
setEntries parents;
setEntries children;
};
typedef std::map<txiter, TxLinks, CompareIteratorByHash> txlinksMap;
txlinksMap mapLinks;
void UpdateParent(txiter entry, txiter parent, bool add);
void UpdateChild(txiter entry, txiter child, bool add);
std::vector<indexed_transaction_set::const_iterator> GetSortedDepthAndScore() const;
public:
indirectmap<COutPoint, const CTransaction*> mapNextTx;
std::map<uint256, CAmount> mapDeltas;
/** Create a new CTxMemPool.
* 建立一個新的交易池
*/
explicit CTxMemPool(CBlockPolicyEstimator* estimator = nullptr);
/**
* If sanity-checking is turned on, check makes sure the pool is
* consistent (does not contain two transactions that spend the same inputs,
* all inputs are in the mapNextTx array). If sanity-checking is turned off,
* check does nothing.
*
**如果開啟了sanity-check，check函式將保證pool的一致性(不包含兩個在同一個輸入中的交易)
* 所有的輸入都在mapNextTx陣列裡；sanity-check關閉，check函式無效
*
*/
void check(const CCoinsViewCache *pcoins) const;
void setSanityCheck(double dFrequency = 1.0) { nCheckFrequency = static_cast<uint32_t>(dFrequency * 4294967295.0); }
// addUnchecked must updated state for all ancestors of a given transaction,
// to track size/count of descendant transactions. First version of
// addUnchecked can be used to have it call CalculateMemPoolAncestors(), and
// then invoke the second version.
// Note that addUnchecked is ONLY called from ATMP outside of tests
// and any other callers may break wallet's in-mempool tracking (due to
// lack of CValidationInterface::TransactionAddedToMempool callbacks).
/**
* addUnchecked函式必先更新祖先交易的狀態
* 第一個addUnchecked函式可以用來呼叫CalculateMemPoolAncestors
* 然後再呼叫第二個addUnchecked
*/
bool addUnchecked(const uint256& hash, const CTxMemPoolEntry &entry, bool validFeeEstimate = true);
bool addUnchecked(const uint256& hash, const CTxMemPoolEntry &entry, setEntries &setAncestors, bool validFeeEstimate = true);
void removeRecursive(const CTransaction &tx, MemPoolRemovalReason reason = MemPoolRemovalReason::UNKNOWN);
void removeForReorg(const CCoinsViewCache *pcoins, unsigned int nMemPoolHeight, int flags);
void removeConflicts(const CTransaction &tx);
void removeForBlock(const std::vector<CTransactionRef>& vtx, unsigned int nBlockHeight);
void clear();
void _clear(); //lock free
bool CompareDepthAndScore(const uint256& hasha, const uint256& hashb);
void queryHashes(std::vector<uint256>& vtxid);
bool isSpent(const COutPoint& outpoint);
unsigned int GetTransactionsUpdated() const;
void AddTransactionsUpdated(unsigned int n);
/**
* Check that none of this transactions inputs are in the mempool, and thus
* the tx is not dependent on other mempool transactions to be included in a block.
**
* 檢查交易的輸入是否在當前交易池中
*/
bool HasNoInputsOf(const CTransaction& tx) const;
/** Affect CreateNewBlock prioritisation of transactions */
//調整CreateNewBlock時的交易優先順序
void PrioritiseTransaction(const uint256& hash, const CAmount& nFeeDelta);
void ApplyDelta(const uint256 hash, CAmount &nFeeDelta) const;
void ClearPrioritisation(const uint256 hash);
public:
/** Remove a set of transactions from the mempool.
* If a transaction is in this set, then all in-mempool descendants must
* also be in the set, unless this transaction is being removed for being
* in a block.
* Set updateDescendants to true when removing a tx that was in a block, so
* that any in-mempool descendants have their ancestor state updated.
**
* 從mempool中移除一個交易集合，
* 如果一個交易在這個集合中，那麼它的所有子孫交易都必須在集合中，
* 除非該交易已經被打包到區塊中。
* 如果要移除一個已經被打包到區塊中的交易，
* 那麼要把updateDescendants設為true，
* 從而更新mempool中所有子孫節點的祖先資訊
*/
void RemoveStaged(setEntries &stage, bool updateDescendants, MemPoolRemovalReason reason = MemPoolRemovalReason::UNKNOWN);
/** When adding transactions from a disconnected block back to the mempool,
* new mempool entries may have children in the mempool (which is generally
* not the case when otherwise adding transactions).
* UpdateTransactionsFromBlock() will find child transactions and update the
* descendant state for each transaction in vHashesToUpdate (excluding any
* child transactions present in vHashesToUpdate, which are already accounted
* for). Note: vHashesToUpdate should be the set of transactions from the
* disconnected block that have been accepted back into the mempool.
**
* 更新每一個交易的所有子孫交易狀態
*
*/
void UpdateTransactionsFromBlock(const std::vector<uint256> &vHashesToUpdate);
/** Try to calculate all in-mempool ancestors of entry.
* (these are all calculated including the tx itself)
* limitAncestorCount = max number of ancestors
* limitAncestorSize = max size of ancestors
* limitDescendantCount = max number of descendants any ancestor can have
* limitDescendantSize = max size of descendants any ancestor can have
* errString = populated with error reason if any limits are hit
* fSearchForParents = whether to search a tx's vin for in-mempool parents, or
* look up parents from mapLinks. Must be true for entries not in the mempool
**
* 計算mempool中所有entry的祖先
* limitAncestorCount = 最大祖先數量
* limitAncestorSize = 最大祖先交易大小
* limitDescendantCount = 任意祖先的最大子孫數量
* limitDescendantSize = 任意祖先的最大子孫大小
* errString = 超過了任何limit限制的錯誤提示
* fSearchForParents = 是否在mempool中搜尋交易的輸入，
* 或者從mapLinks中查詢，對於不在mempool中的entry必須設為true
*/
bool CalculateMemPoolAncestors(const CTxMemPoolEntry &entry, setEntries &setAncestors, uint64_t limitAncestorCount, uint64_t limitAncestorSize, uint64_t limitDescendantCount, uint64_t limitDescendantSize, std::string &errString, bool fSearchForParents = true) const;
/** Populate setDescendants with all in-mempool descendants of hash.
* Assumes that setDescendants includes all in-mempool descendants of anything
* already in it. */
//計算所有子孫交易
void CalculateDescendants(txiter it, setEntries &setDescendants);
/** The minimum fee to get into the mempool, which may itself not be enough
* for larger-sized transactions.
* 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.
**
* 獲取進入交易池需要滿足的最小交易費，本身可能不夠適用於大型交易
* incrementalRelayFee變數用來限制feerate降到0所需的時間
* 當交易費是它的一半時，它被設定為0
*/
CFeeRate GetMinFee(size_t sizelimit) const;
/** Remove transactions from the mempool until its dynamic size is <= sizelimit.
* pvNoSpendsRemaining, if set, will be populated with the list of outpoints
* which are not in mempool which no longer have any spends in this mempool.
**
* 移除所有動態大小超過sizelimit的交易，
* 如果傳入了pvNoSpendsRemaining，那麼將返回不在mempool中並且也沒有
* 任何輸出在mempool的交易列表
*/
void TrimToSize(size_t sizelimit, std::vector<COutPoint>* pvNoSpendsRemaining=nullptr);
/** Expire all transaction (and their dependencies) in the mempool older than time. Return the number of removed transactions. */
/*
** 移除所有在time之前的交易和它的子孫交易，
* 並返回被移除交易的數量
int Expire(int64_t time);
/** Returns false if the transaction is in the mempool and not within the chain limit specified. */
//如果交易不滿足chain limit，返回false
bool TransactionWithinChainLimit(const uint256& txid, size_t chainLimit) const;
unsigned long size()
{
LOCK(cs);
return mapTx.size();
}
uint64_t GetTotalTxSize() const
{
LOCK(cs);
return totalTxSize;
}
bool exists(uint256 hash) const
{
LOCK(cs);
return (mapTx.count(hash) != 0);
}
CTransactionRef get(const uint256& hash) const;
TxMempoolInfo info(const uint256& hash) const;
std::vector<TxMempoolInfo> infoAll() const;
size_t DynamicMemoryUsage() const;
boost::signals2::signal<void (CTransactionRef)> NotifyEntryAdded;
boost::signals2::signal<void (CTransactionRef, MemPoolRemovalReason)> NotifyEntryRemoved;
private:
/** UpdateForDescendants is used by UpdateTransactionsFromBlock to update
* the descendants for a single transaction that has been added to the
* mempool but may have child transactions in the mempool, eg during a
* chain reorg. setExclude is the set of descendant transactions in the
* mempool that must not be accounted for (because any descendants in
* setExclude were added to the mempool after the transaction being
* updated and hence their state is already reflected in the parent
* state).
*
* cachedDescendants will be updated with the descendants of the transaction
* being updated, so that future invocations don't need to walk the
* same transaction again, if encountered in another transaction chain.
**
* UpdateForDescendants 是被 UpdateTransactionsFromBlock 呼叫，
* 用來更新被加入pool中的單個交易的子孫節節點；
* setExclude 是記憶體池中不用更新的子孫交易集合 (because any descendants in
* setExclude were added to the mempool after the transaction being
* updated and hence their state is already reflected in the parent
* state).
*
* 當子孫交易被更新時，cachedDescendants也同時更新
*/
void UpdateForDescendants(txiter updateIt,
cacheMap &cachedDescendants,
const std::set<uint256> &setExclude);
/** Update ancestors of hash to add/remove it as a descendant transaction. */
//更新一個祖先交易去新增或移除 為一個子孫交易
void UpdateAncestorsOf(bool add, txiter hash, setEntries &setAncestors);
/** Set ancestor state for an entry */
//設定一個祖先交易
void UpdateEntryForAncestors(txiter it, const setEntries &setAncestors);
/** For each transaction being removed, update ancestors and any direct children.
* If updateDescendants is true, then also update in-mempool descendants'
* ancestor state. */
/** 對於每一個要移除的交易，更新它的祖先和直接的兒子。
* 如果updateDescendants 設為 true, 那麼還同時更新mempool中子孫的祖先狀態
*/
void UpdateForRemoveFromMempool(const setEntries &entriesToRemove, bool updateDescendants);
/** Sever link between specified transaction and direct children. */
//切斷指定交易與直接子女之間的連結
void UpdateChildrenForRemoval(txiter entry);
/** Before calling removeUnchecked for a given transaction,
* UpdateForRemoveFromMempool must be called on the entire (dependent) set
* of transactions being removed at the same time. We use each
* CTxMemPoolEntry's setMemPoolParents in order to walk ancestors of a
* given transaction that is removed, so we can't remove intermediate
* transactions in a chain before we've updated all the state for the
* removal.
**
* 對於一個特定的交易，呼叫 removeUnchecked 之前，
* 必須為同時為要移除的交易集合呼叫UpdateForRemoveFromMempool。
* 我們使用每個CTxMemPoolEntry中的setMemPoolParents來遍歷
* 要移除交易的祖先，這樣能保證我們更新的正確性。
*/
void removeUnchecked(txiter entry, MemPoolRemovalReason reason = MemPoolRemovalReason::UNKNOWN);
};
複製程式碼有關交易池的概念，光標頭檔案就900多行。我們先大概瞭解下一個交易池(TxMemPool)是由若干個CTxMemPoolEntry構成。然後對交易池某些關鍵函式知道其意思，以後具體遇到了再回過頭來檢視。
. . . .
網際網路顛覆世界，區塊鏈顛覆網際網路!
--------------------------------------------------20180423 23:44