Method CalculateBumpFees

src/node/mini_miner.cpp:309–387

}

std::map<COutPoint, CAmount> MiniMiner::CalculateBumpFees(const CFeeRate& target_feerate)
{
    if (!m_ready_to_calculate) return {};
    // Build a block template until the target feerate is hit.
    BuildMockTemplate(target_feerate);

    // Each transaction that "made it into the block" has a bumpfee of 0, i.e. they are part of an
    // ancestor package with at least the target feerate and don't need to be bumped.
    for (const auto& txid : m_in_block) {
        // Not all of the block transactions were necessarily requested.
        auto it = m_requested_outpoints_by_txid.find(txid);
        if (it != m_requested_outpoints_by_txid.end()) {
            for (const auto& outpoint : it->second) {
                m_bump_fees.emplace(outpoint, 0);
            }
            m_requested_outpoints_by_txid.erase(it);
        }
    }

    // A transactions and its ancestors will only be picked into a block when
    // both the ancestor set feerate and the individual feerate meet the target
    // feerate.
    //
    // We had to convince ourselves that after running the mini miner and
    // picking all eligible transactions into our MockBlockTemplate, there
    // could still be transactions remaining that have a lower individual
    // feerate than their ancestor feerate. So here is an example:
    //
    //               ┌─────────────────┐
    //               │                 │
    //               │   Grandparent   │
    //               │    1700 vB      │
    //               │    1700 sats    │                    Target feerate: 10    s/vB
    //               │       1 s/vB    │    GP Ancestor Set Feerate (ASFR):  1    s/vB
    //               │                 │                           P1_ASFR:  9.84 s/vB
    //               └──────▲───▲──────┘                           P2_ASFR:  2.47 s/vB
    //                      │   │                                   C_ASFR: 10.27 s/vB
    // ┌───────────────┐    │   │    ┌──────────────┐
    // │               ├────┘   └────┤              │             ⇒ C_FR < TFR < C_ASFR
    // │   Parent 1    │             │   Parent 2   │
    // │    200 vB     │             │    200 vB    │
    // │  17000 sats   │             │   3000 sats  │
    // │     85 s/vB   │             │     15 s/vB  │
    // │               │             │              │
    // └───────────▲───┘             └───▲──────────┘
    //             │                     │
    //             │    ┌───────────┐    │
    //             └────┤           ├────┘
    //                  │   Child   │
    //                  │  100 vB   │
    //                  │  900 sats │
    //                  │    9 s/vB │
    //                  │           │
    //                  └───────────┘
    //
    // We therefore calculate both the bump fee that is necessary to elevate
    // the individual transaction to the target feerate:
    //         target_feerate × tx_size - tx_fees