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clusterlin: simplify PickMergeCandidate (optimization)

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The current process consists of iterating over the transactions of the
chunk one by one, and then for each figuring out which of its
parents/children are in unprocessed chunks.

Simplify this (and speed it up slightly) by splitting this process into
two phases: first determine the union of all parents/children, and then
find which chunks those belong to.
This commit is contained in:
Pieter Wuille
2025-12-26 10:50:35 -05:00
committed by Pieter Wuille
parent dcf458ffb9
commit 6f898dbb8b
2 changed files with 45 additions and 34 deletions
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65
src/cluster_linearize.h
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@@ -742,6 +742,22 @@ private:
}
}
/** Find the set of out-of-chunk transactions reachable from tx_idxs. */
template<bool DownWard>
SetType GetReachable(const SetType& tx_idxs) const noexcept
{
SetType ret;
for (auto tx_idx : tx_idxs) {
const auto& tx_data = m_tx_data[tx_idx];
if constexpr (DownWard) {
ret |= tx_data.children;
} else {
ret |= tx_data.parents;
}
}
return ret - tx_idxs;
}
/** Make the inactive dependency from child to parent, which must not be in the same chunk
* already, active. Returns the merged chunk idx. */
SetIdx Activate(TxIdx parent_idx, TxIdx child_idx) noexcept
@@ -883,16 +899,11 @@ private:
/** Information about the chunk. */
Assume(m_chunk_idxs[chunk_idx]);
auto& chunk_info = m_set_info[chunk_idx];
SetType chunk_txn = chunk_info.transactions;
// Iterate over all transactions in the chunk, figuring out which other chunk each
// depends on, but only testing each other chunk once. For those depended-on chunks,
// Iterate over all chunks reachable from this one. For those depended-on chunks,
// remember the highest-feerate (if DownWard) or lowest-feerate (if !DownWard) one.
// If multiple equal-feerate candidate chunks to merge with exist, pick a random one
// among them.
/** Which transactions have been reached from this chunk already. Initialize with the
* chunk itself, so internal dependencies within the chunk are ignored. */
SetType explored = chunk_txn;
/** The minimum feerate (if downward) or maximum feerate (if upward) to consider when
* looking for candidate chunks to merge with. Initially, this is the original chunk's
* feerate, but is updated to be the current best candidate whenever one is found. */
@@ -902,29 +913,29 @@ private:
/** We generate random tiebreak values to pick between equal-feerate candidate chunks.
* This variable stores the tiebreak of the current best candidate. */
uint64_t best_other_chunk_tiebreak{0};
for (auto tx_idx : chunk_txn) {
auto& tx_data = m_tx_data[tx_idx];
/** The transactions reached by following dependencies from tx that have not been
* explored before. */
auto newly_reached = (DownWard ? tx_data.children : tx_data.parents) - explored;
explored |= newly_reached;
while (newly_reached.Any()) {
// Find a chunk inside newly_reached, and remove it from newly_reached.
auto reached_chunk_idx = m_tx_data[newly_reached.First()].chunk_idx;
auto& reached_chunk_info = m_set_info[reached_chunk_idx];
newly_reached -= reached_chunk_info.transactions;
// See if it has an acceptable feerate.
auto cmp = DownWard ? FeeRateCompare(best_other_chunk_feerate, reached_chunk_info.feerate)
: FeeRateCompare(reached_chunk_info.feerate, best_other_chunk_feerate);
if (cmp > 0) continue;
uint64_t tiebreak = m_rng.rand64();
if (cmp < 0 || tiebreak >= best_other_chunk_tiebreak) {
best_other_chunk_feerate = reached_chunk_info.feerate;
best_other_chunk_idx = reached_chunk_idx;
best_other_chunk_tiebreak = tiebreak;
}
/** Which parent/child transactions we still need to process the chunks for. */
auto todo = GetReachable<DownWard>(chunk_info.transactions);
unsigned steps = 0;
while (todo.Any()) {
++steps;
// Find a chunk for a transaction in todo, and remove all its transactions from todo.
auto reached_chunk_idx = m_tx_data[todo.First()].chunk_idx;
auto& reached_chunk_info = m_set_info[reached_chunk_idx];
todo -= reached_chunk_info.transactions;
// See if it has an acceptable feerate.
auto cmp = DownWard ? FeeRateCompare(best_other_chunk_feerate, reached_chunk_info.feerate)
: FeeRateCompare(reached_chunk_info.feerate, best_other_chunk_feerate);
if (cmp > 0) continue;
uint64_t tiebreak = m_rng.rand64();
if (cmp < 0 || tiebreak >= best_other_chunk_tiebreak) {
best_other_chunk_feerate = reached_chunk_info.feerate;
best_other_chunk_idx = reached_chunk_idx;
best_other_chunk_tiebreak = tiebreak;
}
}
Assume(steps <= m_set_info.size());
return best_other_chunk_idx;
}