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txgraph: sort distinct-cluster chunks by equal-feerate-prefix size (feature)

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This makes TxGraph track the equal-feerate-prefix size of all chunks in
all clusters in the main graph, and uses it to sort chunks coming from
distinct clusters.

The order of chunks across clusters becomes:
1. Feerate (high to low)
2. Equal-feerate-prefix (small to large)
3. Cluster sequence number (old to new); this will be changed later.

The equal-feerate-prefix size of a chunk C is defined as the sum
of the weights of all chunks in the same cluster as C, with the same
feerate as C, up to and including C itself, in linearization order (but
excluding such chunks that appear after C).

This is an approximation of sorting chunks from small to large across
clusters, while remaining consistent with intra-cluster linearization
order.
This commit is contained in:
Pieter Wuille
2026-01-07 10:59:24 -05:00
parent e0bc73ba92
commit 8bfbba3207
2 changed files with 72 additions and 2 deletions
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44
src/txgraph.cpp
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@@ -497,14 +497,22 @@ private:
auto feerate_cmp = FeeRateCompare(entry_b.m_main_chunk_feerate, entry_a.m_main_chunk_feerate);
if (feerate_cmp < 0) return std::strong_ordering::less;
if (feerate_cmp > 0) return std::strong_ordering::greater;
// Compare Cluster m_sequence as tie-break for equal chunk feerates.
// Compare equal-feerate chunk prefix size for comparing equal chunk feerates. This does two
// things: it distinguishes equal-feerate chunks within the same cluster (because later
// ones will always have a higher prefix size), and it may distinguish equal-feerate chunks
// from distinct clusters.
if (entry_a.m_main_equal_feerate_chunk_prefix_size != entry_b.m_main_equal_feerate_chunk_prefix_size) {
return entry_a.m_main_equal_feerate_chunk_prefix_size <=> entry_b.m_main_equal_feerate_chunk_prefix_size;
}
// Compare Cluster m_sequence as tie-break for equal chunk feerates in distinct clusters,
// when the equal-feerate-prefix size is also the same.
const auto& locator_a = entry_a.m_locator[0];
const auto& locator_b = entry_b.m_locator[0];
Assume(locator_a.IsPresent() && locator_b.IsPresent());
if (locator_a.cluster != locator_b.cluster) {
return CompareClusters(locator_a.cluster, locator_b.cluster);
}
// As final tie-break, compare position within cluster linearization.
// Within a single chunk, sort by position within cluster linearization.
return entry_a.m_main_lin_index <=> entry_b.m_main_lin_index;
}
@@ -595,6 +603,13 @@ private:
Locator m_locator[MAX_LEVELS];
/** The chunk feerate of this transaction in main (if present in m_locator[0]). */
FeePerWeight m_main_chunk_feerate;
/** The equal-feerate chunk prefix size of this transaction in main. If the transaction is
* part of chunk C in main, then this gives the sum of the sizes of all chunks in C's
* cluster, whose feerate is equal to that of C, which do not appear after C itself in
* the cluster's linearization.
* This provides a way to sort equal-feerate chunks across clusters, in a way that agrees
* with the within-cluster chunk ordering. */
int32_t m_main_equal_feerate_chunk_prefix_size;
/** The position this transaction has in the main linearization (if present). */
LinearizationIndex m_main_lin_index;
};
@@ -1056,11 +1071,23 @@ void GenericClusterImpl::Updated(TxGraphImpl& graph, int level, bool rename) noe
if (level == 0 && (rename || IsAcceptable())) {
auto chunking = ChunkLinearizationInfo(m_depgraph, m_linearization);
LinearizationIndex lin_idx{0};
/** The sum of all chunk feerate FeeFracs with the same feerate as the current chunk,
* up to and including the current chunk. */
FeeFrac equal_feerate_chunk_feerate;
// Iterate over the chunks.
for (unsigned chunk_idx = 0; chunk_idx < chunking.size(); ++chunk_idx) {
auto& chunk = chunking[chunk_idx];
auto chunk_count = chunk.transactions.Count();
Assume(chunk_count > 0);
// Update equal_feerate_chunk_feerate to include this chunk, starting over when the
// feerate changed.
if (chunk.feerate << equal_feerate_chunk_feerate) {
equal_feerate_chunk_feerate = chunk.feerate;
} else {
// Note that this is adding fees to fees, and sizes to sizes, so the overall
// ratio remains the same; it's just accounting for the size of the added chunk.
equal_feerate_chunk_feerate += chunk.feerate;
}
// Iterate over the transactions in the linearization, which must match those in chunk.
while (true) {
DepGraphIndex idx = m_linearization[lin_idx];
@@ -1068,6 +1095,7 @@ void GenericClusterImpl::Updated(TxGraphImpl& graph, int level, bool rename) noe
auto& entry = graph.m_entries[graph_idx];
entry.m_main_lin_index = lin_idx++;
entry.m_main_chunk_feerate = FeePerWeight::FromFeeFrac(chunk.feerate);
entry.m_main_equal_feerate_chunk_prefix_size = equal_feerate_chunk_feerate.size;
Assume(chunk.transactions[idx]);
chunk.transactions.Reset(idx);
if (chunk.transactions.None()) {
@@ -1101,6 +1129,7 @@ void SingletonClusterImpl::Updated(TxGraphImpl& graph, int level, bool rename) n
if (level == 0 && (rename || IsAcceptable())) {
entry.m_main_lin_index = 0;
entry.m_main_chunk_feerate = m_feerate;
entry.m_main_equal_feerate_chunk_prefix_size = m_feerate.size;
// Always use the special LinearizationIndex(-1), indicating singleton chunk at end of
// Cluster, here.
if (!rename) graph.CreateChunkData(m_graph_index, LinearizationIndex(-1));
@@ -2779,6 +2808,8 @@ void GenericClusterImpl::SanityCheck(const TxGraphImpl& graph, int level) const
LinearizationIndex linindex{0};
DepGraphIndex chunk_pos{0}; //!< position within the current chunk
assert(m_depgraph.IsAcyclic());
if (m_linearization.empty()) return;
FeeFrac equal_feerate_prefix = linchunking[chunk_num].feerate;
for (auto lin_pos : m_linearization) {
assert(lin_pos < m_mapping.size());
const auto& entry = graph.m_entries[m_mapping[lin_pos]];
@@ -2795,10 +2826,18 @@ void GenericClusterImpl::SanityCheck(const TxGraphImpl& graph, int level) const
assert(entry.m_main_lin_index == linindex);
++linindex;
if (!linchunking[chunk_num].transactions[lin_pos]) {
// First transaction of a new chunk.
++chunk_num;
chunk_pos = 0;
if (linchunking[chunk_num].feerate << equal_feerate_prefix) {
equal_feerate_prefix = linchunking[chunk_num].feerate;
} else {
assert(!(linchunking[chunk_num].feerate >> equal_feerate_prefix));
equal_feerate_prefix += linchunking[chunk_num].feerate;
}
}
assert(entry.m_main_chunk_feerate == linchunking[chunk_num].feerate);
assert(entry.m_main_equal_feerate_chunk_prefix_size == equal_feerate_prefix.size);
// Verify that an entry in the chunk index exists for every chunk-ending transaction.
++chunk_pos;
if (graph.m_main_clusterset.m_to_remove.empty()) {
@@ -2834,6 +2873,7 @@ void SingletonClusterImpl::SanityCheck(const TxGraphImpl& graph, int level) cons
if (level == 0 && IsAcceptable()) {
assert(entry.m_main_lin_index == 0);
assert(entry.m_main_chunk_feerate == m_feerate);
assert(entry.m_main_equal_feerate_chunk_prefix_size == m_feerate.size);
if (graph.m_main_clusterset.m_to_remove.empty()) {
assert(entry.m_main_chunkindex_iterator != graph.m_main_chunkindex.end());
auto& chunk_data = *entry.m_main_chunkindex_iterator;