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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
View File

@ -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;
}

14
src/test/util/cluster_linearize.h
View File

@ -403,13 +403,13 @@ inline uint64_t MaxOptimalLinearizationIters(DepGraphIndex cluster_count)
static constexpr uint64_t ITERS[65] = {
0,
0, 4, 10, 34, 76, 156, 229, 380,
432, 607, 738, 896, 1037, 1366, 1464, 1711,
2060, 2542, 3068, 3116, 4029, 3467, 5324, 5402,
6481, 7161, 7441, 8329, 8843, 9353, 11104, 11269,
11791, 11981, 12413, 14259, 15331, 12397, 13581, 18569,
18737, 16581, 23217, 23271, 27350, 28591, 33636, 34486,
34414, 26227, 35570, 38045, 40814, 29622, 37793, 32122,
35915, 49823, 39722, 43765, 42365, 53620, 59417, 67035
432, 517, 678, 896, 1037, 1366, 1479, 1711,
2060, 2542, 3068, 3116, 4029, 3467, 5324, 5512,
6481, 7161, 7441, 8183, 8843, 9353, 11104, 11269,
12354, 11871, 13367, 14259, 14229, 12397, 13581, 17774,
18737, 16581, 23217, 24044, 29597, 28879, 34069, 34162,
36028, 26227, 34471, 37212, 40814, 29554, 40305, 34019,
36582, 55659, 39994, 41277, 42365, 52822, 60151, 67035
};
assert(cluster_count < std::size(ITERS));
// Multiply the table number by two, to account for the fact that they are not absolutes.