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clusterlin: keep track of active children (optimization)

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This means we can iterate over all active dependencies in a
cluster/chunk in O(ntx) time rather than O(ndeps) (*), as the number of
active dependencies in a set of transactions of size is at most ntx-1.

(*) Asymptotically, this is not actually true, as for large transaction
counts, iterating over a BitSet still scales with ntx. In practice
however, where BitSets are represented by a constant number of integers,
it holds.
This commit is contained in:
Pieter Wuille 2026-01-11 19:23:58 -05:00 committed by Pieter Wuille
parent ae16485aa9
commit 63b06d5523
1 changed files with 18 additions and 16 deletions
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34
src/cluster_linearize.h
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@ -665,13 +665,14 @@ private:
/** Structure with information about a single transaction. */
struct TxData {
/** The top set for every active child dependency this transaction has, indexed by child
* TxIdx. INVALID_SET_IDX if there is no active dependency with the corresponding child.
*/
* TxIdx. Only defined for indexes in active_children. */
std::array<SetIdx, SetType::Size()> dep_top_idx;
/** The set of parent transactions of this transaction. Immutable after construction. */
SetType parents;
/** The set of child transactions of this transaction. Immutable after construction. */
SetType children;
/** The set of child transactions reachable through an active dependency. */
SetType active_children;
/** Which chunk this transaction belongs to. */
SetIdx chunk_idx;
};
@ -733,9 +734,7 @@ private:
tx_data.chunk_idx = chunk_idx;
// Iterate over all active dependencies with tx_idx as parent. Combined with the outer
// loop this iterates over all internal active dependencies of the chunk.
for (auto child_idx : tx_data.children) {
// Skip inactive dependencies.
if (tx_data.dep_top_idx[child_idx] == INVALID_SET_IDX) continue;
for (auto child_idx : tx_data.active_children) {
auto& top_set_info = m_set_info[tx_data.dep_top_idx[child_idx]];
// If this dependency's top set contains query, update it to add/remove
// dep_change.
@ -771,7 +770,7 @@ private:
auto& parent_data = m_tx_data[parent_idx];
auto& child_data = m_tx_data[child_idx];
Assume(parent_data.children[child_idx]);
Assume(parent_data.dep_top_idx[child_idx] == INVALID_SET_IDX);
Assume(!parent_data.active_children[child_idx]);
// Get the set index of the chunks the parent and child are currently in. The parent chunk
// will become the top set of the newly activated dependency, while the child chunk will be
// grown to become the merged chunk.
@ -821,6 +820,7 @@ private:
m_reachable[child_chunk_idx].second -= bottom_info.transactions;
// Make parent chunk the set for the new active dependency.
parent_data.dep_top_idx[child_idx] = parent_chunk_idx;
parent_data.active_children.Set(child_idx);
m_chunk_idxs.Reset(parent_chunk_idx);
// Return the newly merged chunk.
return child_chunk_idx;
@ -833,7 +833,7 @@ private:
// Gather and check information about the parent transactions.
auto& parent_data = m_tx_data[parent_idx];
Assume(parent_data.children[child_idx]);
Assume(parent_data.dep_top_idx[child_idx] != INVALID_SET_IDX);
Assume(parent_data.active_children[child_idx]);
// Get the top set of the active dependency (which will become the parent chunk) and the
// chunk set the transactions are currently in (which will become the bottom chunk).
auto parent_chunk_idx = parent_data.dep_top_idx[child_idx];
@ -845,7 +845,7 @@ private:
auto& bottom_info = m_set_info[child_chunk_idx];
// Remove the active dependency.
parent_data.dep_top_idx[child_idx] = INVALID_SET_IDX;
parent_data.active_children.Reset(child_idx);
m_chunk_idxs.Set(parent_chunk_idx);
m_cost += bottom_info.transactions.Count();
// Subtract the top_info from the bottom_info, as it will become the child chunk.
@ -1044,8 +1044,7 @@ private:
for (auto tx_idx : chunk_info.transactions) {
const auto& tx_data = m_tx_data[tx_idx];
// Iterate over all active child dependencies of the transaction.
for (auto child_idx : tx_data.children) {
if (tx_data.dep_top_idx[child_idx] == INVALID_SET_IDX) continue;
for (auto child_idx : tx_data.active_children) {
auto& dep_top_info = m_set_info[tx_data.dep_top_idx[child_idx]];
// Skip if this dependency is ineligible (the top chunk that would be created
// does not have higher feerate than the chunk it is currently part of).
@ -1086,8 +1085,6 @@ public:
// Create a singleton chunk for it.
tx_data.chunk_idx = num_chunks;
m_set_info[num_chunks++] = SetInfo(depgraph, tx_idx);
// Mark all its dependencies inactive.
tx_data.dep_top_idx.fill(INVALID_SET_IDX);
}
// Set the reachable transactions for each chunk to the transactions' parents and children.
for (SetIdx chunk_idx = 0; chunk_idx < num_transactions; ++chunk_idx) {
@ -1232,9 +1229,7 @@ public:
for (auto tx_idx : chunk_info.transactions) {
const auto& tx_data = m_tx_data[tx_idx];
// Iterate over all active child dependencies of the transaction.
for (auto child_idx : tx_data.children) {
// Skip inactive child dependencies.
if (tx_data.dep_top_idx[child_idx] == INVALID_SET_IDX) continue;
for (auto child_idx : tx_data.active_children) {
const auto& dep_top_info = m_set_info[tx_data.dep_top_idx[child_idx]];
// Skip if this dependency does not have equal top and bottom set feerates. Note
// that the top cannot have higher feerate than the bottom, or OptimizeSteps would
@ -1497,7 +1492,7 @@ public:
for (auto tx_idx : m_transaction_idxs) {
for (auto child_idx : m_tx_data[tx_idx].children) {
all_dependencies.emplace_back(tx_idx, child_idx);
if (m_tx_data[tx_idx].dep_top_idx[child_idx] != INVALID_SET_IDX) {
if (m_tx_data[tx_idx].active_children[child_idx]) {
active_dependencies.emplace_back(tx_idx, child_idx);
}
}
@ -1564,6 +1559,13 @@ public:
// Verify parents/children.
assert(tx_data.parents == m_depgraph.GetReducedParents(tx_idx));
assert(tx_data.children == m_depgraph.GetReducedChildren(tx_idx));
// Verify active_children is a subset of children.
assert(tx_data.active_children.IsSubsetOf(tx_data.children));
// Verify each active child's dep_top_idx points to a valid non-chunk set.
for (auto child_idx : tx_data.active_children) {
assert(tx_data.dep_top_idx[child_idx] < m_set_info.size());
assert(!m_chunk_idxs[tx_data.dep_top_idx[child_idx]]);
}
}
//