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Implement Mini version of BlockAssembler to calculate mining scores

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Rewrite the same algo instead of reusing BlockAssembler because we have
a few extra requirements that would make the changes invasive and
difficult to review:

- Only operate on the relevant transactions rather than full mempool
- Remove transactions that will be replaced so they can't bump their ancestors
- Don't hold mempool lock outside of the constructor
- Skip things like max block weight and IsFinalTx
- Additionally calculate fees to bump remaining ancestor packages to target feerate

Co-authored-by: Murch <murch@murch.one>
This commit is contained in:
glozow 2022-08-04 15:37:50 +01:00 • committed by Murch
parent 56484f0fdc
commit 59afcc8354
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2
src/Makefile.am
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@ -211,6 +211,7 @@ BITCOIN_CORE_H = \
node/mempool_args.h \
node/mempool_persist_args.h \
node/miner.h \
node/mini_miner.h \
node/minisketchwrapper.h \
node/psbt.h \
node/transaction.h \
@ -396,6 +397,7 @@ libbitcoin_node_a_SOURCES = \
node/mempool_args.cpp \
node/mempool_persist_args.cpp \
node/miner.cpp \
node/mini_miner.cpp \
node/minisketchwrapper.cpp \
node/psbt.cpp \
node/transaction.cpp \

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src/node/mini_miner.cpp Normal file
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// Copyright (c) 2023 The Bitcoin Core developers
// Distributed under the MIT software license, see the accompanying
// file COPYING or http://www.opensource.org/licenses/mit-license.php.
#include <node/mini_miner.h>
#include <consensus/amount.h>
#include <policy/feerate.h>
#include <primitives/transaction.h>
#include <timedata.h>
#include <util/check.h>
#include <util/moneystr.h>
#include <algorithm>
#include <numeric>
#include <utility>
namespace node {
MiniMiner::MiniMiner(const CTxMemPool& mempool, const std::vector<COutPoint>& outpoints)
{
LOCK(mempool.cs);
// Find which outpoints to calculate bump fees for.
// Anything that's spent by the mempool is to-be-replaced
// Anything otherwise unavailable just has a bump fee of 0
for (const auto& outpoint : outpoints) {
if (!mempool.exists(GenTxid::Txid(outpoint.hash))) {
// This UTXO is either confirmed or not yet submitted to mempool.
// If it's confirmed, no bump fee is required.
// If it's not yet submitted, we have no information, so return 0.
m_bump_fees.emplace(outpoint, 0);
continue;
}
// UXTO is created by transaction in mempool, add to map.
// Note: This will either create a missing entry or add the outpoint to an existing entry
m_requested_outpoints_by_txid[outpoint.hash].push_back(outpoint);
if (const auto ptx{mempool.GetConflictTx(outpoint)}) {
// This outpoint is already being spent by another transaction in the mempool. We
// assume that the caller wants to replace this transaction and its descendants. It
// would be unusual for the transaction to have descendants as the wallet won’t normally
// attempt to replace transactions with descendants. If the outpoint is from a mempool
// transaction, we still need to calculate its ancestors bump fees (added to
// m_requested_outpoints_by_txid below), but after removing the to-be-replaced entries.
//
// Note that the descendants of a transaction include the transaction itself. Also note,
// that this is only calculating bump fees. RBF fee rules should be handled separately.
CTxMemPool::setEntries descendants;
mempool.CalculateDescendants(mempool.GetIter(ptx->GetHash()).value(), descendants);
for (const auto& desc_txiter : descendants) {
m_to_be_replaced.insert(desc_txiter->GetTx().GetHash());
}
}
}
// No unconfirmed UTXOs, so nothing mempool-related needs to be calculated.
if (m_requested_outpoints_by_txid.empty()) return;
// Calculate the cluster and construct the entry map.
std::vector<uint256> txids_needed;
txids_needed.reserve(m_requested_outpoints_by_txid.size());
for (const auto& [txid, _]: m_requested_outpoints_by_txid) {
txids_needed.push_back(txid);
}
const auto cluster = mempool.GatherClusters(txids_needed);
if (cluster.empty()) {
// An empty cluster means that at least one of the transactions is missing from the mempool
// (should not be possible given processing above) or DoS limit was hit.
m_ready_to_calculate = false;
return;
}
// Add every entry to m_entries_by_txid and m_entries, except the ones that will be replaced.
for (const auto& txiter : cluster) {
if (!m_to_be_replaced.count(txiter->GetTx().GetHash())) {
auto [mapiter, success] = m_entries_by_txid.emplace(txiter->GetTx().GetHash(), MiniMinerMempoolEntry(txiter));
m_entries.push_back(mapiter);
} else {
auto outpoints_it = m_requested_outpoints_by_txid.find(txiter->GetTx().GetHash());
if (outpoints_it != m_requested_outpoints_by_txid.end()) {
// This UTXO is the output of a to-be-replaced transaction. Bump fee is 0; spending
// this UTXO is impossible as it will no longer exist after the replacement.
for (const auto& outpoint : outpoints_it->second) {
m_bump_fees.emplace(outpoint, 0);
}
m_requested_outpoints_by_txid.erase(outpoints_it);
}
}
}
// Build the m_descendant_set_by_txid cache.
for (const auto& txiter : cluster) {
const auto& txid = txiter->GetTx().GetHash();
// Cache descendants for future use. Unlike the real mempool, a descendant MiniMinerMempoolEntry
// will not exist without its ancestor MiniMinerMempoolEntry, so these sets won't be invalidated.
std::vector<MockEntryMap::iterator> cached_descendants;
const bool remove{m_to_be_replaced.count(txid) > 0};
CTxMemPool::setEntries descendants;
mempool.CalculateDescendants(txiter, descendants);
Assume(descendants.count(txiter) > 0);
for (const auto& desc_txiter : descendants) {
const auto txid_desc = desc_txiter->GetTx().GetHash();
const bool remove_desc{m_to_be_replaced.count(txid_desc) > 0};
auto desc_it{m_entries_by_txid.find(txid_desc)};
Assume((desc_it == m_entries_by_txid.end()) == remove_desc);
if (remove) Assume(remove_desc);
// It's possible that remove=false but remove_desc=true.
if (!remove && !remove_desc) {
cached_descendants.push_back(desc_it);
}
}
if (remove) {
Assume(cached_descendants.empty());
} else {
m_descendant_set_by_txid.emplace(txid, cached_descendants);
}
}
// Release the mempool lock; we now have all the information we need for a subset of the entries
// we care about. We will solely operate on the MiniMinerMempoolEntry map from now on.
Assume(m_in_block.empty());
Assume(m_requested_outpoints_by_txid.size() <= outpoints.size());
SanityCheck();
}
// Compare by min(ancestor feerate, individual feerate), then iterator
//
// Under the ancestor-based mining approach, high-feerate children can pay for parents, but high-feerate
// parents do not incentive inclusion of their children. Therefore the mining algorithm only considers
// transactions for inclusion on basis of the minimum of their own feerate or their ancestor feerate.
struct AncestorFeerateComparator
{
template<typename I>
bool operator()(const I& a, const I& b) const {
auto min_feerate = [](const MiniMinerMempoolEntry& e) -> CFeeRate {
const CAmount ancestor_fee{e.GetModFeesWithAncestors()};
const int64_t ancestor_size{e.GetSizeWithAncestors()};
const CAmount tx_fee{e.GetModifiedFee()};
const int64_t tx_size{e.GetTxSize()};
// Comparing ancestor feerate with individual feerate:
// ancestor_fee / ancestor_size <= tx_fee / tx_size
// Avoid division and possible loss of precision by
// multiplying both sides by the sizes:
return ancestor_fee * tx_size < tx_fee * ancestor_size ?
CFeeRate(ancestor_fee, ancestor_size) :
CFeeRate(tx_fee, tx_size);
};
CFeeRate a_feerate{min_feerate(a->second)};
CFeeRate b_feerate{min_feerate(b->second)};
if (a_feerate != b_feerate) {
return a_feerate > b_feerate;
}
// Use txid as tiebreaker for stable sorting
return a->first < b->first;
}
};
void MiniMiner::DeleteAncestorPackage(const std::set<MockEntryMap::iterator, IteratorComparator>& ancestors)
{
Assume(ancestors.size() >= 1);
// "Mine" all transactions in this ancestor set.
for (auto& anc : ancestors) {
Assume(m_in_block.count(anc->first) == 0);
m_in_block.insert(anc->first);
m_total_fees += anc->second.GetModifiedFee();
m_total_vsize += anc->second.GetTxSize();
auto it = m_descendant_set_by_txid.find(anc->first);
// Each entry’s descendant set includes itself
Assume(it != m_descendant_set_by_txid.end());
for (auto& descendant : it->second) {
// If these fail, we must be double-deducting.
Assume(descendant->second.GetModFeesWithAncestors() >= anc->second.GetModifiedFee());
Assume(descendant->second.vsize_with_ancestors >= anc->second.GetTxSize());
descendant->second.fee_with_ancestors -= anc->second.GetModifiedFee();
descendant->second.vsize_with_ancestors -= anc->second.GetTxSize();
}
}
// Delete these entries.
for (const auto& anc : ancestors) {
m_descendant_set_by_txid.erase(anc->first);
// The above loop should have deducted each ancestor's size and fees from each of their
// respective descendants exactly once.
Assume(anc->second.GetModFeesWithAncestors() == 0);
Assume(anc->second.GetSizeWithAncestors() == 0);
auto vec_it = std::find(m_entries.begin(), m_entries.end(), anc);
Assume(vec_it != m_entries.end());
m_entries.erase(vec_it);
m_entries_by_txid.erase(anc);
}
}
void MiniMiner::SanityCheck() const
{
// m_entries, m_entries_by_txid, and m_descendant_set_by_txid all same size
Assume(m_entries.size() == m_entries_by_txid.size());
Assume(m_entries.size() == m_descendant_set_by_txid.size());
// Cached ancestor values should be at least as large as the transaction's own fee and size
Assume(std::all_of(m_entries.begin(), m_entries.end(), [](const auto& entry) {
return entry->second.GetSizeWithAncestors() >= entry->second.GetTxSize() &&
entry->second.GetModFeesWithAncestors() >= entry->second.GetModifiedFee();}));
// None of the entries should be to-be-replaced transactions
Assume(std::all_of(m_to_be_replaced.begin(), m_to_be_replaced.end(),
[&](const auto& txid){return m_entries_by_txid.find(txid) == m_entries_by_txid.end();}));
}
void MiniMiner::BuildMockTemplate(const CFeeRate& target_feerate)
{
while (!m_entries_by_txid.empty()) {
// Sort again, since transaction removal may change some m_entries' ancestor feerates.
std::sort(m_entries.begin(), m_entries.end(), AncestorFeerateComparator());
// Pick highest ancestor feerate entry.
auto best_iter = m_entries.begin();
Assume(best_iter != m_entries.end());
const auto ancestor_package_size = (*best_iter)->second.GetSizeWithAncestors();
const auto ancestor_package_fee = (*best_iter)->second.GetModFeesWithAncestors();
// Stop here. Everything that didn't "make it into the block" has bumpfee.
if (ancestor_package_fee < target_feerate.GetFee(ancestor_package_size)) {
break;
}
// Calculate ancestors on the fly. This lookup should be fairly cheap, and ancestor sets
// change at every iteration, so this is more efficient than maintaining a cache.
std::set<MockEntryMap::iterator, IteratorComparator> ancestors;
{
std::set<MockEntryMap::iterator, IteratorComparator> to_process;
to_process.insert(*best_iter);
while (!to_process.empty()) {
auto iter = to_process.begin();
Assume(iter != to_process.end());
ancestors.insert(*iter);
for (const auto& input : (*iter)->second.GetTx().vin) {
if (auto parent_it{m_entries_by_txid.find(input.prevout.hash)}; parent_it != m_entries_by_txid.end()) {
if (ancestors.count(parent_it) == 0) {
to_process.insert(parent_it);
}
}
}
to_process.erase(iter);
}
}
DeleteAncestorPackage(ancestors);
SanityCheck();
}
Assume(m_in_block.empty() || m_total_fees >= target_feerate.GetFee(m_total_vsize));
// Do not try to continue building the block template with a different feerate.
m_ready_to_calculate = false;
}
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
// and the bump fee that is necessary to bump the entire ancestor set to
// the target feerate:
// target_feerate × ancestor_set_size - ancestor_set_fees
// By picking the maximum from the two, we ensure that a transaction meets
// both criteria.
for (const auto& [txid, outpoints] : m_requested_outpoints_by_txid) {
auto it = m_entries_by_txid.find(txid);
Assume(it != m_entries_by_txid.end());
if (it != m_entries_by_txid.end()) {
Assume(target_feerate.GetFee(it->second.GetSizeWithAncestors()) > std::min(it->second.GetModifiedFee(), it->second.GetModFeesWithAncestors()));
CAmount bump_fee_with_ancestors = target_feerate.GetFee(it->second.GetSizeWithAncestors()) - it->second.GetModFeesWithAncestors();
CAmount bump_fee_individual = target_feerate.GetFee(it->second.GetTxSize()) - it->second.GetModifiedFee();
const CAmount bump_fee{std::max(bump_fee_with_ancestors, bump_fee_individual)};
Assume(bump_fee >= 0);
for (const auto& outpoint : outpoints) {
m_bump_fees.emplace(outpoint, bump_fee);
}
}
}
return m_bump_fees;
}
std::optional<CAmount> MiniMiner::CalculateTotalBumpFees(const CFeeRate& target_feerate)
{
if (!m_ready_to_calculate) return std::nullopt;
// Build a block template until the target feerate is hit.
BuildMockTemplate(target_feerate);
// All remaining ancestors that are not part of m_in_block must be bumped, but no other relatives
std::set<MockEntryMap::iterator, IteratorComparator> ancestors;
std::set<MockEntryMap::iterator, IteratorComparator> to_process;
for (const auto& [txid, outpoints] : m_requested_outpoints_by_txid) {
// Skip any ancestors that already have a miner score higher than the target feerate
// (already "made it" into the block)
if (m_in_block.count(txid)) continue;
auto iter = m_entries_by_txid.find(txid);
if (iter == m_entries_by_txid.end()) continue;
to_process.insert(iter);
ancestors.insert(iter);
}
while (!to_process.empty()) {
auto iter = to_process.begin();
const CTransaction& tx = (*iter)->second.GetTx();
for (const auto& input : tx.vin) {
if (auto parent_it{m_entries_by_txid.find(input.prevout.hash)}; parent_it != m_entries_by_txid.end()) {
to_process.insert(parent_it);
ancestors.insert(parent_it);
}
}
to_process.erase(iter);
}
const auto ancestor_package_size = std::accumulate(ancestors.cbegin(), ancestors.cend(), int64_t{0},
[](int64_t sum, const auto it) {return sum + it->second.GetTxSize();});
const auto ancestor_package_fee = std::accumulate(ancestors.cbegin(), ancestors.cend(), CAmount{0},
[](CAmount sum, const auto it) {return sum + it->second.GetModifiedFee();});
return target_feerate.GetFee(ancestor_package_size) - ancestor_package_fee;
}
} // namespace node

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// Copyright (c) 2022 The Bitcoin Core developers
// Distributed under the MIT software license, see the accompanying
// file COPYING or http://www.opensource.org/licenses/mit-license.php.
#ifndef BITCOIN_NODE_MINI_MINER_H
#define BITCOIN_NODE_MINI_MINER_H
#include <txmempool.h>
#include <memory>
#include <optional>
#include <stdint.h>
namespace node {
// Container for tracking updates to ancestor feerate as we include ancestors in the "block"
class MiniMinerMempoolEntry
{
const CAmount fee_individual;
const CTransactionRef tx;
const int64_t vsize_individual;
// This class must be constructed while holding mempool.cs. After construction, the object's
// methods can be called without holding that lock.
public:
CAmount fee_with_ancestors;
int64_t vsize_with_ancestors;
explicit MiniMinerMempoolEntry(CTxMemPool::txiter entry) :
fee_individual{entry->GetModifiedFee()},
tx{entry->GetSharedTx()},
vsize_individual(entry->GetTxSize()),
fee_with_ancestors{entry->GetModFeesWithAncestors()},
vsize_with_ancestors(entry->GetSizeWithAncestors())
{ }
CAmount GetModifiedFee() const { return fee_individual; }
CAmount GetModFeesWithAncestors() const { return fee_with_ancestors; }
int64_t GetTxSize() const { return vsize_individual; }
int64_t GetSizeWithAncestors() const { return vsize_with_ancestors; }
const CTransaction& GetTx() const LIFETIMEBOUND { return *tx; }
};
// Comparator needed for std::set<MockEntryMap::iterator>
struct IteratorComparator
{
template<typename I>
bool operator()(const I& a, const I& b) const
{
return &(*a) < &(*b);
}
};
/** A minimal version of BlockAssembler. Allows us to run the mining algorithm on a subset of
* mempool transactions, ignoring consensus rules, to calculate mining scores. */
class MiniMiner
{
// When true, a caller may use CalculateBumpFees(). Becomes false if we failed to retrieve
// mempool entries (i.e. cluster size too large) or bump fees have already been calculated.
bool m_ready_to_calculate{true};
// Set once per lifetime, fill in during initialization.
// txids of to-be-replaced transactions
std::set<uint256> m_to_be_replaced;
// If multiple argument outpoints correspond to the same transaction, cache them together in
// a single entry indexed by txid. Then we can just work with txids since all outpoints from
// the same tx will have the same bumpfee. Excludes non-mempool transactions.
std::map<uint256, std::vector<COutPoint>> m_requested_outpoints_by_txid;
// What we're trying to calculate.
std::map<COutPoint, CAmount> m_bump_fees;
// The constructed block template
std::set<uint256> m_in_block;
// Information on the current status of the block
CAmount m_total_fees{0};
int32_t m_total_vsize{0};
/** Main data structure holding the entries, can be indexed by txid */
std::map<uint256, MiniMinerMempoolEntry> m_entries_by_txid;
using MockEntryMap = decltype(m_entries_by_txid);
/** Vector of entries, can be sorted by ancestor feerate. */
std::vector<MockEntryMap::iterator> m_entries;
/** Map of txid to its descendants. Should be inclusive. */
std::map<uint256, std::vector<MockEntryMap::iterator>> m_descendant_set_by_txid;
/** Consider this ancestor package "mined" so remove all these entries from our data structures. */
void DeleteAncestorPackage(const std::set<MockEntryMap::iterator, IteratorComparator>& ancestors);
/** Perform some checks. */
void SanityCheck() const;
public:
/** Returns true if CalculateBumpFees may be called, false if not. */
bool IsReadyToCalculate() const { return m_ready_to_calculate; }
/** Build a block template until the target feerate is hit. */
void BuildMockTemplate(const CFeeRate& target_feerate);
/** Returns set of txids in the block template if one has been constructed. */
std::set<uint256> GetMockTemplateTxids() const { return m_in_block; }
MiniMiner(const CTxMemPool& mempool, const std::vector<COutPoint>& outpoints);
/** Construct a new block template and, for each outpoint corresponding to a transaction that
* did not make it into the block, calculate the cost of bumping those transactions (and their
* ancestors) to the minimum feerate. Returns a map from outpoint to bump fee, or an empty map
* if they cannot be calculated. */
std::map<COutPoint, CAmount> CalculateBumpFees(const CFeeRate& target_feerate);
/** Construct a new block template and, calculate the cost of bumping all transactions that did
* not make it into the block to the target feerate. Returns the total bump fee, or std::nullopt
* if it cannot be calculated. */
std::optional<CAmount> CalculateTotalBumpFees(const CFeeRate& target_feerate);
};
} // namespace node
#endif // BITCOIN_NODE_MINI_MINER_H