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Merge bitcoin/bitcoin#32191: Make TxGraph fuzz tests more deterministic
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Browse source 
2835216ec0 txgraph: make GroupClusters use partition numbers directly (optimization) (Pieter Wuille)
c72c8d5d45 txgraph: compare sequence numbers instead of Cluster* (bugfix) (Pieter Wuille)

Pull request description:

  Part of cluster mempool: #30289

  The implicit transaction ordering for transactions in a TxGraphImpl is defined by:
  1. higher chunk feerate first
  2. lower Cluster* object pointer first
  3. lower position within cluster linearization first.

  Number (2) is not deterministic, as it intricately depends on the heap allocation algorithm. Fix this by giving each Cluster a unique `uint64_t m_sequence` value, and sorting by those instead.

  The second commit then uses this new approach to optimize GroupClusters a bit more, avoiding some repeated checks and dereferences, by making a local copy of the involved sequence numbers.

  Thanks to @dergoegge for pointing this out.

ACKs for top commit:
  instagibbs:
    reACK 2835216ec0
  marcofleon:
    ACK 2835216ec0
  glozow:
    utACK 2835216ec0

Tree-SHA512: d772a55b9ed620159b934a42a39fca7f900d4aa89c099a280a0c61ea0bd7c4fc39b388281ffc775064ea77b0b17263871b4c9763aa71c710a79287d5eb2cd4b4
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merge-script 2025-04-17 13:50:48 -04:00
commit 247e9de622
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2 changed files with 101 additions and 75 deletions
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13
src/test/fuzz/txgraph.cpp
View file

@ -206,11 +206,14 @@ struct SimTxGraph
ret.push_back(ptr);
}
}
// Deduplicate.
std::sort(ret.begin(), ret.end());
ret.erase(std::unique(ret.begin(), ret.end()), ret.end());
// Replace input.
arg = std::move(ret);
// Construct deduplicated version in input (do not use std::sort/std::unique for
// deduplication as it'd rely on non-deterministic pointer comparison).
arg.clear();
for (auto ptr : ret) {
if (std::find(arg.begin(), arg.end(), ptr) == arg.end()) {
arg.push_back(ptr);
}
}
}
};

163
src/txgraph.cpp
View file

@ -70,12 +70,16 @@ class Cluster
ClusterSetIndex m_setindex{ClusterSetIndex(-1)};
/** Which level this Cluster is at in the graph (-1=not inserted, 0=main, 1=staging). */
int m_level{-1};
/** Sequence number for this Cluster (for tie-breaking comparison between equal-chunk-feerate
transactions in distinct clusters). */
uint64_t m_sequence;
public:
Cluster() noexcept = delete;
/** Construct an empty Cluster. */
Cluster() noexcept = default;
explicit Cluster(uint64_t sequence) noexcept;
/** Construct a singleton Cluster. */
explicit Cluster(TxGraphImpl& graph, const FeePerWeight& feerate, GraphIndex graph_index) noexcept;
explicit Cluster(uint64_t sequence, TxGraphImpl& graph, const FeePerWeight& feerate, GraphIndex graph_index) noexcept;
// Cannot move or copy (would invalidate Cluster* in Locator and ClusterSet). */
Cluster(const Cluster&) = delete;
@ -157,6 +161,7 @@ public:
void SanityCheck(const TxGraphImpl& graph, int level) const;
};
/** The transaction graph, including staged changes.
*
* The overall design of the data structure consists of 3 interlinked representations:
@ -244,6 +249,8 @@ private:
ClusterSet m_main_clusterset;
/** The staging ClusterSet, if any. */
std::optional<ClusterSet> m_staging_clusterset;
/** Next sequence number to assign to created Clusters. */
uint64_t m_next_sequence_counter{0};
/** A Locator that describes whether, where, and in which Cluster an Entry appears.
* Every Entry has MAX_LEVELS locators, as it may appear in one Cluster per level.
@ -315,6 +322,18 @@ private:
/** Set of Entries which have no linked Ref anymore. */
std::vector<GraphIndex> m_unlinked;
/** Compare two Cluster* by their m_sequence value (while supporting nullptr). */
static std::strong_ordering CompareClusters(Cluster* a, Cluster* b) noexcept
{
// The nullptr pointer compares before everything else.
if (a == nullptr || b == nullptr) {
return (a != nullptr) <=> (b != nullptr);
}
// If neither pointer is nullptr, compare the Clusters' sequence numbers.
Assume(a == b || a->m_sequence != b->m_sequence);
return a->m_sequence <=> b->m_sequence;
}
public:
/** Construct a new TxGraphImpl with the specified maximum cluster count. */
explicit TxGraphImpl(DepGraphIndex max_cluster_count) noexcept :
@ -569,7 +588,7 @@ std::vector<Cluster*> TxGraphImpl::GetConflicts() const noexcept
}
}
// Deduplicate the result (the same Cluster may appear multiple times).
std::sort(ret.begin(), ret.end());
std::sort(ret.begin(), ret.end(), [](Cluster* a, Cluster* b) noexcept { return CompareClusters(a, b) < 0; });
ret.erase(std::unique(ret.begin(), ret.end()), ret.end());
return ret;
}
@ -577,7 +596,7 @@ std::vector<Cluster*> TxGraphImpl::GetConflicts() const noexcept
Cluster* Cluster::CopyToStaging(TxGraphImpl& graph) const noexcept
{
// Construct an empty Cluster.
auto ret = std::make_unique<Cluster>();
auto ret = std::make_unique<Cluster>(graph.m_next_sequence_counter++);
auto ptr = ret.get();
// Copy depgraph, mapping, and linearization/
ptr->m_depgraph = m_depgraph;
@ -710,7 +729,7 @@ bool Cluster::Split(TxGraphImpl& graph) noexcept
}
first = false;
// Construct a new Cluster to hold the found component.
auto new_cluster = std::make_unique<Cluster>();
auto new_cluster = std::make_unique<Cluster>(graph.m_next_sequence_counter++);
new_clusters.push_back(new_cluster.get());
// Remember that all the component's transactions go to this new Cluster. The positions
// will be determined below, so use -1 for now.
@ -956,9 +975,11 @@ void TxGraphImpl::ApplyRemovals(int up_to_level) noexcept
if (cluster != nullptr) PullIn(cluster);
}
}
// Group the set of to-be-removed entries by Cluster*.
// Group the set of to-be-removed entries by Cluster::m_sequence.
std::sort(to_remove.begin(), to_remove.end(), [&](GraphIndex a, GraphIndex b) noexcept {
return std::less{}(m_entries[a].m_locator[level].cluster, m_entries[b].m_locator[level].cluster);
Cluster* cluster_a = m_entries[a].m_locator[level].cluster;
Cluster* cluster_b = m_entries[b].m_locator[level].cluster;
return CompareClusters(cluster_a, cluster_b) < 0;
});
// Process per Cluster.
std::span to_remove_span{to_remove};
@ -1082,38 +1103,37 @@ void TxGraphImpl::GroupClusters(int level) noexcept
// with inefficient and/or oversized Clusters which just end up being split again anyway.
SplitAll(level);
/** Annotated clusters: an entry for each Cluster, together with the representative for the
* partition it is in if known, or with nullptr if not yet known. */
std::vector<std::pair<Cluster*, Cluster*>> an_clusters;
/** Annotated clusters: an entry for each Cluster, together with the sequence number for the
* representative for the partition it is in (initially its own, later that of the
* to-be-merged group). */
std::vector<std::pair<Cluster*, uint64_t>> an_clusters;
/** Annotated dependencies: an entry for each m_deps_to_add entry (excluding ones that apply
* to removed transactions), together with the representative root of the partition of
* Clusters it applies to. */
std::vector<std::pair<std::pair<GraphIndex, GraphIndex>, Cluster*>> an_deps;
* to removed transactions), together with the sequence number of the representative root of
* Clusters it applies to (initially that of the child Cluster, later that of the
* to-be-merged group). */
std::vector<std::pair<std::pair<GraphIndex, GraphIndex>, uint64_t>> an_deps;
// Construct a an_clusters entry for every parent and child in the to-be-applied dependencies.
// Construct a an_clusters entry for every parent and child in the to-be-applied dependencies,
// and an an_deps entry for each dependency to be applied.
an_deps.reserve(clusterset.m_deps_to_add.size());
for (const auto& [par, chl] : clusterset.m_deps_to_add) {
auto par_cluster = FindCluster(par, level);
auto chl_cluster = FindCluster(chl, level);
// Skip dependencies for which the parent or child transaction is removed.
if (par_cluster == nullptr || chl_cluster == nullptr) continue;
an_clusters.emplace_back(par_cluster, nullptr);
an_clusters.emplace_back(par_cluster, par_cluster->m_sequence);
// Do not include a duplicate when parent and child are identical, as it'll be removed
// below anyway.
if (chl_cluster != par_cluster) an_clusters.emplace_back(chl_cluster, nullptr);
if (chl_cluster != par_cluster) an_clusters.emplace_back(chl_cluster, chl_cluster->m_sequence);
// Add entry to an_deps, using the child sequence number.
an_deps.emplace_back(std::pair{par, chl}, chl_cluster->m_sequence);
}
// Sort and deduplicate an_clusters, so we end up with a sorted list of all involved Clusters
// to which dependencies apply.
std::sort(an_clusters.begin(), an_clusters.end());
std::sort(an_clusters.begin(), an_clusters.end(), [](auto& a, auto& b) noexcept { return a.second < b.second; });
an_clusters.erase(std::unique(an_clusters.begin(), an_clusters.end()), an_clusters.end());
// Sort the dependencies by child Cluster.
std::sort(clusterset.m_deps_to_add.begin(), clusterset.m_deps_to_add.end(), [&](auto& a, auto& b) noexcept {
auto [_a_par, a_chl] = a;
auto [_b_par, b_chl] = b;
auto a_chl_cluster = FindCluster(a_chl, level);
auto b_chl_cluster = FindCluster(b_chl, level);
return std::less{}(a_chl_cluster, b_chl_cluster);
});
// Sort an_deps by applying the same order to the involved child cluster.
std::sort(an_deps.begin(), an_deps.end(), [&](auto& a, auto& b) noexcept { return a.second < b.second; });
// Run the union-find algorithm to to find partitions of the input Clusters which need to be
// grouped together. See https://en.wikipedia.org/wiki/Disjoint-set_data_structure.
@ -1121,8 +1141,8 @@ void TxGraphImpl::GroupClusters(int level) noexcept
/** Each PartitionData entry contains information about a single input Cluster. */
struct PartitionData
{
/** The cluster this holds information for. */
Cluster* cluster;
/** The sequence number of the cluster this holds information for. */
uint64_t sequence;
/** All PartitionData entries belonging to the same partition are organized in a tree.
* Each element points to its parent, or to itself if it is the root. The root is then
* a representative for the entire tree, and can be found by walking upwards from any
@ -1132,15 +1152,15 @@ void TxGraphImpl::GroupClusters(int level) noexcept
* tree for this partition. */
unsigned rank;
};
/** Information about each input Cluster. Sorted by Cluster* pointer. */
/** Information about each input Cluster. Sorted by Cluster::m_sequence. */
std::vector<PartitionData> partition_data;
/** Given a Cluster, find its corresponding PartitionData. */
auto locate_fn = [&](Cluster* arg) noexcept -> PartitionData* {
auto it = std::lower_bound(partition_data.begin(), partition_data.end(), arg,
[](auto& a, Cluster* ptr) noexcept { return a.cluster < ptr; });
auto locate_fn = [&](uint64_t sequence) noexcept -> PartitionData* {
auto it = std::lower_bound(partition_data.begin(), partition_data.end(), sequence,
[](auto& a, uint64_t seq) noexcept { return a.sequence < seq; });
Assume(it != partition_data.end());
Assume(it->cluster == arg);
Assume(it->sequence == sequence);
return &*it;
};
@ -1175,65 +1195,57 @@ void TxGraphImpl::GroupClusters(int level) noexcept
// Start by initializing every Cluster as its own singleton partition.
partition_data.resize(an_clusters.size());
for (size_t i = 0; i < an_clusters.size(); ++i) {
partition_data[i].cluster = an_clusters[i].first;
partition_data[i].sequence = an_clusters[i].first->m_sequence;
partition_data[i].parent = &partition_data[i];
partition_data[i].rank = 0;
}
// Run through all parent/child pairs in m_deps_to_add, and union the
// the partitions their Clusters are in.
// Run through all parent/child pairs in an_deps, and union the partitions their Clusters
// are in.
Cluster* last_chl_cluster{nullptr};
PartitionData* last_partition{nullptr};
for (const auto& [par, chl] : clusterset.m_deps_to_add) {
for (const auto& [dep, _] : an_deps) {
auto [par, chl] = dep;
auto par_cluster = FindCluster(par, level);
auto chl_cluster = FindCluster(chl, level);
Assume(chl_cluster != nullptr && par_cluster != nullptr);
// Nothing to do if parent and child are in the same Cluster.
if (par_cluster == chl_cluster) continue;
// Nothing to do if either parent or child transaction is removed already.
if (par_cluster == nullptr || chl_cluster == nullptr) continue;
Assume(par != chl);
if (chl_cluster == last_chl_cluster) {
// If the child Clusters is the same as the previous iteration, union with the
// tree they were in, avoiding the need for another lookup. Note that m_deps_to_add
// tree they were in, avoiding the need for another lookup. Note that an_deps
// is sorted by child Cluster, so batches with the same child are expected.
last_partition = union_fn(locate_fn(par_cluster), last_partition);
last_partition = union_fn(locate_fn(par_cluster->m_sequence), last_partition);
} else {
last_chl_cluster = chl_cluster;
last_partition = union_fn(locate_fn(par_cluster), locate_fn(chl_cluster));
last_partition = union_fn(locate_fn(par_cluster->m_sequence), locate_fn(chl_cluster->m_sequence));
}
}
// Populate the an_clusters and an_deps data structures with the list of input Clusters,
// and the input dependencies, annotated with the representative of the Cluster partition
// it applies to.
an_deps.reserve(clusterset.m_deps_to_add.size());
auto deps_it = clusterset.m_deps_to_add.begin();
// Update the sequence numbers in an_clusters and an_deps to be those of the partition
// representative.
auto deps_it = an_deps.begin();
for (size_t i = 0; i < partition_data.size(); ++i) {
auto& data = partition_data[i];
// Find the representative of the partition Cluster i is in, and store it with the
// Cluster.
auto rep = find_root_fn(&data)->cluster;
Assume(an_clusters[i].second == nullptr);
an_clusters[i].second = rep;
// Find the sequence of the representative of the partition Cluster i is in, and store
// it with the Cluster.
auto rep_seq = find_root_fn(&data)->sequence;
an_clusters[i].second = rep_seq;
// Find all dependencies whose child Cluster is Cluster i, and annotate them with rep.
while (deps_it != clusterset.m_deps_to_add.end()) {
auto [par, chl] = *deps_it;
while (deps_it != an_deps.end()) {
auto [par, chl] = deps_it->first;
auto chl_cluster = FindCluster(chl, level);
if (std::greater{}(chl_cluster, data.cluster)) break;
// Skip dependencies that apply to earlier Clusters (those necessary are for
// deleted transactions, as otherwise we'd have processed them already).
if (chl_cluster == data.cluster) {
auto par_cluster = FindCluster(par, level);
// Also filter out dependencies applying to a removed parent.
if (par_cluster != nullptr) an_deps.emplace_back(*deps_it, rep);
}
Assume(chl_cluster != nullptr);
if (chl_cluster->m_sequence > data.sequence) break;
deps_it->second = rep_seq;
++deps_it;
}
}
}
// Sort both an_clusters and an_deps by representative of the partition they are in, grouping
// all those applying to the same partition together.
// Sort both an_clusters and an_deps by sequence number of the representative of the
// partition they are in, grouping all those applying to the same partition together.
std::sort(an_deps.begin(), an_deps.end(), [](auto& a, auto& b) noexcept { return a.second < b.second; });
std::sort(an_clusters.begin(), an_clusters.end(), [](auto& a, auto& b) noexcept { return a.second < b.second; });
@ -1390,7 +1402,10 @@ void TxGraphImpl::MakeAllAcceptable(int level) noexcept
}
}
Cluster::Cluster(TxGraphImpl& graph, const FeePerWeight& feerate, GraphIndex graph_index) noexcept
Cluster::Cluster(uint64_t sequence) noexcept : m_sequence{sequence} {}
Cluster::Cluster(uint64_t sequence, TxGraphImpl& graph, const FeePerWeight& feerate, GraphIndex graph_index) noexcept :
m_sequence{sequence}
{
// Create a new transaction in the DepGraph, and remember its position in m_mapping.
auto cluster_idx = m_depgraph.AddTransaction(feerate);
@ -1410,7 +1425,7 @@ TxGraph::Ref TxGraphImpl::AddTransaction(const FeePerWeight& feerate) noexcept
GetRefGraph(ret) = this;
GetRefIndex(ret) = idx;
// Construct a new singleton Cluster (which is necessarily optimally linearized).
auto cluster = std::make_unique<Cluster>(*this, feerate, idx);
auto cluster = std::make_unique<Cluster>(m_next_sequence_counter++, *this, feerate, idx);
auto cluster_ptr = cluster.get();
int level = GetTopLevel();
auto& clusterset = GetClusterSet(level);
@ -1606,7 +1621,7 @@ std::vector<TxGraph::Ref*> TxGraphImpl::GetAncestorsUnion(std::span<const Ref* c
matches.emplace_back(cluster, m_entries[GetRefIndex(*arg)].m_locator[cluster->m_level].index);
}
// Group by Cluster.
std::sort(matches.begin(), matches.end(), [](auto& a, auto& b) noexcept { return std::less{}(a.first, b.first); });
std::sort(matches.begin(), matches.end(), [](auto& a, auto& b) noexcept { return CompareClusters(a.first, b.first) < 0; });
// Dispatch to the Clusters.
std::span match_span(matches);
std::vector<TxGraph::Ref*> ret;
@ -1639,7 +1654,7 @@ std::vector<TxGraph::Ref*> TxGraphImpl::GetDescendantsUnion(std::span<const Ref*
matches.emplace_back(cluster, m_entries[GetRefIndex(*arg)].m_locator[cluster->m_level].index);
}
// Group by Cluster.
std::sort(matches.begin(), matches.end(), [](auto& a, auto& b) noexcept { return std::less{}(a.first, b.first); });
std::sort(matches.begin(), matches.end(), [](auto& a, auto& b) noexcept { return CompareClusters(a.first, b.first) < 0; });
// Dispatch to the Clusters.
std::span match_span(matches);
std::vector<TxGraph::Ref*> ret;
@ -1867,7 +1882,9 @@ std::strong_ordering TxGraphImpl::CompareMainOrder(const Ref& a, const Ref& b) n
if (feerate_cmp < 0) return std::strong_ordering::less;
if (feerate_cmp > 0) return std::strong_ordering::greater;
// Compare Cluster* as tie-break for equal chunk feerates.
if (locator_a.cluster != locator_b.cluster) return locator_a.cluster <=> locator_b.cluster;
if (locator_a.cluster != locator_b.cluster) {
return CompareClusters(locator_a.cluster, locator_b.cluster);
}
// As final tie-break, compare position within cluster linearization.
return entry_a.m_main_lin_index <=> entry_b.m_main_lin_index;
}
@ -1889,7 +1906,7 @@ TxGraph::GraphIndex TxGraphImpl::CountDistinctClusters(std::span<const Ref* cons
if (cluster != nullptr) clusters.push_back(cluster);
}
// Count the number of distinct elements in clusters.
std::sort(clusters.begin(), clusters.end());
std::sort(clusters.begin(), clusters.end(), [](Cluster* a, Cluster* b) noexcept { return CompareClusters(a, b) < 0; });
Cluster* last{nullptr};
GraphIndex ret{0};
for (Cluster* cluster : clusters) {
@ -1951,6 +1968,8 @@ void TxGraphImpl::SanityCheck() const
std::set<const Cluster*> expected_clusters[MAX_LEVELS];
/** Which GraphIndexes ought to occur in ClusterSet::m_removed, based on m_entries. */
std::set<GraphIndex> expected_removed[MAX_LEVELS];
/** Which Cluster::m_sequence values have been encountered. */
std::set<uint64_t> sequences;
/** Whether compaction is possible in the current state. */
bool compact_possible{true};
@ -2004,6 +2023,10 @@ void TxGraphImpl::SanityCheck() const
// ... for all clusters in them ...
for (ClusterSetIndex setindex = 0; setindex < quality_clusters.size(); ++setindex) {
const auto& cluster = *quality_clusters[setindex];
// Check the sequence number.
assert(cluster.m_sequence < m_next_sequence_counter);
assert(sequences.count(cluster.m_sequence) == 0);
sequences.insert(cluster.m_sequence);
// Remember we saw this Cluster (only if it is non-empty; empty Clusters aren't
// expected to be referenced by the Entry vector).
if (cluster.GetTxCount() != 0) {