Method addPackageTxs

src/node/miner.cpp:373–518

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 selec

// mapModifiedTxs with the next transaction in the mempool to decide what
// transaction package to work on next.
void BlockAssembler::addPackageTxs(int& nPackagesSelected, int& nDescendantsUpdated, std::chrono::seconds min_tx_age)
{
    AssertLockHeld(m_mempool.cs);

    // 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);

    // ELEMENTS: we use confidential_score instead of ancestor_score
    CTxMemPool::indexed_transaction_set::index<confidential_score>::type::iterator mi = m_mempool.mapTx.get<confidential_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;
    constexpr int32_t BLOCK_FULL_ENOUGH_WEIGHT_DELTA = 4000;
    int64_t nConsecutiveFailed = 0;

    while (mi != m_mempool.mapTx.get<confidential_score>().end() || !mapModifiedTx.empty()) {
        // First try to find a new transaction in mapTx to evaluate.
        if (mi != m_mempool.mapTx.get<confidential_score>().end() &&
            SkipMapTxEntry(m_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;

        modconftxscoreiter modit = mapModifiedTx.get<confidential_score>().begin();
        if (mi == m_mempool.mapTx.get<confidential_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 = m_mempool.mapTx.project<0>(mi);
            if (modit != mapModifiedTx.get<confidential_score>().end() &&
                    CompareTxMemPoolEntryByConfidentialFee()(*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;
            }
        }