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txgraph: Track multiple potential would-be clusters in Trim (improvement)

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In the existing Trim function, as soon as the set of accepted transactions
would exceed the max cluster size or count limit, the acceptance loop is
stopped, removing all later transactions. However, it is possible that by
excluding some of those transactions the would-be cluster splits apart into
multiple would-clusters. And those clusters may well permit far more
transactions before their limits are reached.

Take this into account by using a union-find structure inside TrimTxData to
keep track of the count/size of all would-be clusters that would be formed
at any point, and only reject transactions which would cause these resulting
partitions to exceed their limits.

This is not an optimization in terms of CPU usage or memory; it just
improves the quality of the transactions removed by Trim().
This commit is contained in:
Pieter Wuille
2024-12-19 23:06:07 -05:00
parent 4608df37e0
commit 1632fc104b
3 changed files with 131 additions and 53 deletions
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28
src/test/txgraph_tests.cpp
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@@ -68,14 +68,11 @@ BOOST_AUTO_TEST_CASE(txgraph_trim_zigzag)
graph->SanityCheck();
BOOST_CHECK(!graph->IsOversized(/*main_only=*/false));
BOOST_CHECK_EQUAL(removed_refs.size(), NUM_TOTAL_TX - MAX_CLUSTER_COUNT);
BOOST_CHECK_EQUAL(graph->GetTransactionCount(), MAX_CLUSTER_COUNT);
// Only prefix of size max_cluster_count is left. That's the first half of the top and first half of the bottom.
// We only need to trim the middle bottom transaction to end up with 2 clusters each within cluster limits.
BOOST_CHECK_EQUAL(removed_refs.size(), 1);
BOOST_CHECK_EQUAL(graph->GetTransactionCount(), MAX_CLUSTER_COUNT * 2 - 2);
for (unsigned int i = 0; i < refs.size(); ++i) {
const bool first_half = (i < (NUM_BOTTOM_TX / 2)) ||
(i >= NUM_BOTTOM_TX && i < NUM_BOTTOM_TX + NUM_TOP_TX / 2 + 1);
BOOST_CHECK_EQUAL(graph->Exists(refs[i]), first_half);
BOOST_CHECK_EQUAL(graph->Exists(refs[i]), i != (NUM_BOTTOM_TX / 2));
}
}
@@ -129,13 +126,12 @@ BOOST_AUTO_TEST_CASE(txgraph_trim_flower)
graph->SanityCheck();
BOOST_CHECK(!graph->IsOversized(/*main_only=*/false));
BOOST_CHECK_EQUAL(removed_refs.size(), NUM_TOTAL_TX - MAX_CLUSTER_COUNT);
BOOST_CHECK_EQUAL(graph->GetTransactionCount(), MAX_CLUSTER_COUNT);
// Only prefix of size max_cluster_count (last max_cluster_count top transactions) is left.
for (unsigned int i = 0; i < refs.size(); ++i) {
const bool top_highest_feerate = i > (NUM_TOTAL_TX - MAX_CLUSTER_COUNT - 1);
BOOST_CHECK_EQUAL(graph->Exists(refs[i]), top_highest_feerate);
// Since only the bottom transaction connects these clusters, we only need to remove it.
BOOST_CHECK_EQUAL(removed_refs.size(), 1);
BOOST_CHECK_EQUAL(graph->GetTransactionCount(false), MAX_CLUSTER_COUNT * 2);
BOOST_CHECK(!graph->Exists(refs[0]));
for (unsigned int i = 1; i < refs.size(); ++i) {
BOOST_CHECK(graph->Exists(refs[i]));
}
}
@@ -248,8 +244,8 @@ BOOST_AUTO_TEST_CASE(txgraph_trim_huge)
BOOST_CHECK(removed_refs.size() == total_tx_count - graph->GetTransactionCount());
graph->SanityCheck();
// At least one original chain must survive.
BOOST_CHECK(graph->GetTransactionCount() >= NUM_TX_PER_TOP_CHAIN);
// At least 99% of chains must survive.
BOOST_CHECK(graph->GetTransactionCount() >= (NUM_TOP_CHAINS * NUM_TX_PER_TOP_CHAIN * 99) / 100);
}
BOOST_AUTO_TEST_CASE(txgraph_trim_big_singletons)