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txgraph: Avoid looking up the same child cluster repeatedly (optimization)

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Since m_deps_to_add has been sorted by child Cluster* already, all dependencies
with the same child will be processed consecutively. Take advantage of this by
remember the last partition merged with, and reusing that if applicable.
This commit is contained in:
Pieter Wuille 2025-01-22 14:36:00 -05:00
parent 1171953ac6
commit 57f5499882
1 changed files with 15 additions and 3 deletions
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18
src/txgraph.cpp
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@ -784,18 +784,20 @@ void TxGraphImpl::GroupClusters() noexcept
return data;
};
/** Given two PartitionDatas, union the partitions they are in. */
/** Given two PartitionDatas, union the partitions they are in, and return their
* representative. */
static constexpr auto union_fn = [](PartitionData* arg1, PartitionData* arg2) noexcept {
// Find the roots of the trees, and bail out if they are already equal (which would
// mean they are in the same partition already).
auto rep1 = find_root_fn(arg1);
auto rep2 = find_root_fn(arg2);
if (rep1 == rep2) return;
if (rep1 == rep2) return rep1;
// Pick the lower-rank root to become a child of the higher-rank one.
// See https://en.wikipedia.org/wiki/Disjoint-set_data_structure#Union_by_rank.
if (rep1->rank < rep2->rank) std::swap(rep1, rep2);
rep2->parent = rep1;
rep1->rank += (rep1->rank == rep2->rank);
return rep1;
};
// Start by initializing every Cluster as its own singleton partition.
@ -808,6 +810,8 @@ void TxGraphImpl::GroupClusters() noexcept
// Run through all parent/child pairs in m_deps_to_add, and union the
// the partitions their Clusters are in.
Cluster* last_chl_cluster{nullptr};
PartitionData* last_partition{nullptr};
for (const auto& [par, chl] : m_deps_to_add) {
auto par_cluster = m_entries[par].m_locator.cluster;
auto chl_cluster = m_entries[chl].m_locator.cluster;
@ -816,7 +820,15 @@ void TxGraphImpl::GroupClusters() noexcept
// Nothing to do if either parent or child transaction is removed already.
if (par_cluster == nullptr || chl_cluster == nullptr) continue;
Assume(par != chl);
union_fn(locate_fn(par_cluster), locate_fn(chl_cluster));
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
// is sorted by child Cluster, so batches with the same child are expected.
last_partition = union_fn(locate_fn(par_cluster), last_partition);
} else {
last_chl_cluster = chl_cluster;
last_partition = union_fn(locate_fn(par_cluster), locate_fn(chl_cluster));
}
}
// Populate the an_clusters and an_deps data structures with the list of input Clusters,