// This transaction selection algorithm orders the mempool based
// on feerate of a transaction including all unconfirmed ancestors.
// Since we don't remove transactions from the mempool as we select them
// for block inclusion, we need an alternate method of updating the feerate
// of a transaction with its not-yet-selected ancestors as we go.
// This is accomplished by walking the in-mempool descendants of selected
// transactions and storing a temporary modified state in mapModifiedTxs.
// Each time through the loop, we compare the best transaction in
// mapModifiedTxs with the next transaction in the mempool to decide what
// transaction package to work on next.
void BlockAssembler::addPackageTxs(int &nPackagesSelected, int &nDescendantsUpdated)
{
// mapModifiedTx will store sorted packages after they are modified
// because some of their txs are already in the block
indexed_modified_transaction_set mapModifiedTx;
// Keep track of entries that failed inclusion, to avoid duplicate work
CTxMemPool::setEntries failedTx;
// Start by adding all descendants of previously added txs to mapModifiedTx
// and modifying them for their already included ancestors
UpdatePackagesForAdded(inBlock, mapModifiedTx);
CTxMemPool::indexed_transaction_set::index<ancestor_score>::type::iterator mi = mempool.mapTx.get<ancestor_score>().begin();
CTxMemPool::txiter iter;
// Limit the number of attempts to add transactions to the block when it is
// close to full; this is just a simple heuristic to finish quickly if the
// mempool has a lot of entries.
const int64_t MAX_CONSECUTIVE_FAILURES = 1000;
int64_t nConsecutiveFailed = 0;
while (mi != mempool.mapTx.get<ancestor_score>().end() || !mapModifiedTx.empty())
{
// First try to find a new transaction in mapTx to evaluate.
if (mi != mempool.mapTx.get<ancestor_score>().end() &&
SkipMapTxEntry(mempool.mapTx.project<0>(mi), mapModifiedTx, failedTx)) {
++mi;
continue;
}
// Now that mi is not stale, determine which transaction to evaluate:
// the next entry from mapTx, or the best from mapModifiedTx?
bool fUsingModified = false;
modtxscoreiter modit = mapModifiedTx.get<ancestor_score>().begin();
if (mi == mempool.mapTx.get<ancestor_score>().end()) {
// We're out of entries in mapTx; use the entry from mapModifiedTx
iter = modit->iter;
fUsingModified = true;
} else {
// Try to compare the mapTx entry to the mapModifiedTx entry
iter = mempool.mapTx.project<0>(mi);
if (modit != mapModifiedTx.get<ancestor_score>().end() &&
CompareModifiedEntry()(*modit, CTxMemPoolModifiedEntry(iter))) {
// The best entry in mapModifiedTx has higher score
// than the one from mapTx.
// Switch which transaction (package) to consider
iter = modit->iter;
fUsingModified = true;
} else {
// Either no entry in mapModifiedTx, or it's worse than mapTx.
// Increment mi for the next loop iteration.
++mi;
}
}
// We skip mapTx entries that are inBlock, and mapModifiedTx shouldn't
// contain anything that is inBlock.
assert(!inBlock.count(iter));
uint64_t packageSize = iter->GetSizeWithAncestors();
CAmount packageFees = iter->GetModFeesWithAncestors();
int64_t packageSigOpsCost = iter->GetSigOpCostWithAncestors();
if (fUsingModified) {
packageSize = modit->nSizeWithAncestors;
packageFees = modit->nModFeesWithAncestors;
packageSigOpsCost = modit->nSigOpCostWithAncestors;
}
if (packageFees < blockMinFeeRate.GetFee(packageSize)) {
// Everything else we might consider has a lower fee rate
return;
}
if (!TestPackage(packageSize, packageSigOpsCost)) {
if (fUsingModified) {
// Since we always look at the best entry in mapModifiedTx,
// we must erase failed entries so that we can consider the
// next best entry on the next loop iteration
mapModifiedTx.get<ancestor_score>().erase(modit);
failedTx.insert(iter);
}
++nConsecutiveFailed;
if (nConsecutiveFailed > MAX_CONSECUTIVE_FAILURES && nBlockWeight >
nBlockMaxWeight - 4000) {
// Give up if we're close to full and haven't succeeded in a while
break;
}
continue;
}
CTxMemPool::setEntries ancestors;
uint64_t nNoLimit = std::numeric_limits<uint64_t>::max();
std::string dummy;
mempool.CalculateMemPoolAncestors(*iter, ancestors, nNoLimit, nNoLimit, nNoLimit, nNoLimit, dummy, false);
onlyUnconfirmed(ancestors);
ancestors.insert(iter);
// Test if all tx's are Final
if (!TestPackageTransactions(ancestors)) {
if (fUsingModified) {
mapModifiedTx.get<ancestor_score>().erase(modit);
failedTx.insert(iter);
}
continue;
}
// This transaction will make it in; reset the failed counter.
nConsecutiveFailed = 0;
// Package can be added. Sort the entries in a valid order.
std::vector<CTxMemPool::txiter> sortedEntries;
SortForBlock(ancestors, iter, sortedEntries);
for (size_t i=0; i<sortedEntries.size(); ++i) {
AddToBlock(sortedEntries[i]);
// Erase from the modified set, if present
mapModifiedTx.erase(sortedEntries[i]);
}
++nPackagesSelected;
// Update transactions that depend on each of these
nDescendantsUpdated += UpdatePackagesForAdded(ancestors, mapModifiedTx);
}
}
void CTxMemPool::check(const CCoinsViewCache *pcoins) const
{
LOCK(cs);
if (nCheckFrequency == 0)
return;
if (GetRand(std::numeric_limits<uint32_t>::max()) >= nCheckFrequency)
return;
LogPrint(BCLog::MEMPOOL, "Checking mempool with %u transactions and %u inputs\n", (unsigned int)mapTx.size(), (unsigned int)mapNextTx.size());
uint64_t checkTotal = 0;
uint64_t innerUsage = 0;
CCoinsViewCache mempoolDuplicate(const_cast<CCoinsViewCache*>(pcoins));
const int64_t spendheight = GetSpendHeight(mempoolDuplicate);
std::list<const CTxMemPoolEntry*> waitingOnDependants;
for (indexed_transaction_set::const_iterator it = mapTx.begin(); it != mapTx.end(); it++) {
unsigned int i = 0;
checkTotal += it->GetTxSize();
innerUsage += it->DynamicMemoryUsage();
const CTransaction& tx = it->GetTx();
txlinksMap::const_iterator linksiter = mapLinks.find(it);
assert(linksiter != mapLinks.end());
const TxLinks &links = linksiter->second;
innerUsage += memusage::DynamicUsage(links.parents) + memusage::DynamicUsage(links.children);
bool fDependsWait = false;
setEntries setParentCheck;
int64_t parentSizes = 0;
int64_t parentSigOpCost = 0;
for (const CTxIn &txin : tx.vin) {
// Check that every mempool transaction's inputs refer to available coins, or other mempool tx's.
indexed_transaction_set::const_iterator it2 = mapTx.find(txin.prevout.hash);
if (it2 != mapTx.end()) {
const CTransaction& tx2 = it2->GetTx();
assert(tx2.vout.size() > txin.prevout.n && !tx2.vout[txin.prevout.n].IsNull());
fDependsWait = true;
if (setParentCheck.insert(it2).second) {
parentSizes += it2->GetTxSize();
parentSigOpCost += it2->GetSigOpCost();
}
} else {
assert(pcoins->HaveCoin(txin.prevout));
}
// Check whether its inputs are marked in mapNextTx.
auto it3 = mapNextTx.find(txin.prevout);
assert(it3 != mapNextTx.end());
assert(it3->first == &txin.prevout);
assert(it3->second == &tx);
i++;
}
assert(setParentCheck == GetMemPoolParents(it));
// Verify ancestor state is correct.
setEntries setAncestors;
uint64_t nNoLimit = std::numeric_limits<uint64_t>::max();
std::string dummy;
CalculateMemPoolAncestors(*it, setAncestors, nNoLimit, nNoLimit, nNoLimit, nNoLimit, dummy);
uint64_t nCountCheck = setAncestors.size() + 1;
uint64_t nSizeCheck = it->GetTxSize();
CAmount nFeesCheck = it->GetModifiedFee();
int64_t nSigOpCheck = it->GetSigOpCost();
for (txiter ancestorIt : setAncestors) {
nSizeCheck += ancestorIt->GetTxSize();
nFeesCheck += ancestorIt->GetModifiedFee();
nSigOpCheck += ancestorIt->GetSigOpCost();
}
assert(it->GetCountWithAncestors() == nCountCheck);
assert(it->GetSizeWithAncestors() == nSizeCheck);
assert(it->GetSigOpCostWithAncestors() == nSigOpCheck);
assert(it->GetModFeesWithAncestors() == nFeesCheck);
// Check children against mapNextTx
CTxMemPool::setEntries setChildrenCheck;
auto iter = mapNextTx.lower_bound(COutPoint(it->GetTx().GetHash(), 0));
int64_t childSizes = 0;
for (; iter != mapNextTx.end() && iter->first->hash == it->GetTx().GetHash(); ++iter) {
txiter childit = mapTx.find(iter->second->GetHash());
assert(childit != mapTx.end()); // mapNextTx points to in-mempool transactions
if (setChildrenCheck.insert(childit).second) {
childSizes += childit->GetTxSize();
}
}
assert(setChildrenCheck == GetMemPoolChildren(it));
// Also check to make sure size is greater than sum with immediate children.
// just a sanity check, not definitive that this calc is correct...
assert(it->GetSizeWithDescendants() >= childSizes + it->GetTxSize());
if (fDependsWait)
waitingOnDependants.push_back(&(*it));
else {
CheckInputsAndUpdateCoins(tx, mempoolDuplicate, spendheight);
}
}
unsigned int stepsSinceLastRemove = 0;
while (!waitingOnDependants.empty()) {
const CTxMemPoolEntry* entry = waitingOnDependants.front();
waitingOnDependants.pop_front();
CValidationState state;
if (!mempoolDuplicate.HaveInputs(entry->GetTx())) {
waitingOnDependants.push_back(entry);
stepsSinceLastRemove++;
assert(stepsSinceLastRemove < waitingOnDependants.size());
} else {
CheckInputsAndUpdateCoins(entry->GetTx(), mempoolDuplicate, spendheight);
stepsSinceLastRemove = 0;
}
}
for (auto it = mapNextTx.cbegin(); it != mapNextTx.cend(); it++) {
uint256 hash = it->second->GetHash();
indexed_transaction_set::const_iterator it2 = mapTx.find(hash);
const CTransaction& tx = it2->GetTx();
assert(it2 != mapTx.end());
assert(&tx == it->second);
}
assert(totalTxSize == checkTotal);
assert(innerUsage == cachedInnerUsage);
}