Merge bitcoin/bitcoin#29724: 29242 Diagram check followups

ee1b9b231a0a7e89b77cbf8ea54e0534f0970dd0 CalculateFeerateDiagramsForRBF: update misleading description of old diagram contents (Greg Sanders)
a9d42b9aa579f54922ffd17fdeb61e704539b92c CompareFeerateDiagram: short-circuit comparison when detected as incomparable (Greg Sanders)
cebcced65e8fdbd54893d4852d5ed6b85a8b0c45 remove erroneous CompareFeerateDiagram comment about slope (Greg Sanders)
a0376e106182075634e50c14da00e84b4069b985 unit test: clarify unstated assumption for calc_feerate_diagram_rbf chunking (Greg Sanders)
890cb015f3b99c4f2f57a1bbc69e5cf2045c2739 s/effected/affected/ (Greg Sanders)
d9391ec0952920bdbb10d3f6e9e706e85f717ec0 CalculateFeerateDiagramsForRBF: remove size tie-breaking from chunking conflicts (Greg Sanders)
b684d82d7e093889a8dc7678c6d6605ca4cd9fa4 fuzz: Add more invariant checks for package_rbf (Greg Sanders)
2a3ada8b2181b45165608947c7c42b341d0a54dd fuzz: finer grained ImprovesFeerateDiagram check on error result (Greg Sanders)
c377ae9ba08150c467e8b6cfaac7865f4d31457c unit test: improve ImprovesFeerateDiagram coverage with one less vb case (Greg Sanders)
d2bf923eb19f6330bad673b71faadec582780aa1 unit test: make calc_feerate_diagram_rbf less brittle (Greg Sanders)
defe023f6ec49dd64c6e03880cee0e9299b45762 fuzz: add PrioritiseTransaction coverage in diagram checks (Greg Sanders)
216d5ff1627be6562312b5afb477078ed8495999 unit test: add coverage showing priority affects diagram check results (Greg Sanders)
a80d80936a8de487569d00755d0fbcd058a94823 unit test: add CheckConflictTopology case for not the only child (Greg Sanders)
69bd18ca80007584be4089b3f42650d351854bb3 unit test: check tx4 conflict error message (Greg Sanders)
c0c37f07eb0fb4027faa04e5457f8421264e8ad5 unit test: have CompareFeerateDiagram tested with diagrams both ways (Greg Sanders)
b62e2c0fa5f6010ff1fc60c59418d0796b83c5de ImprovesFeerateDiagram: Spelling fix and removal of unused diagram vectors (Greg Sanders)
bb424029459af691c4d07988f3d76afeaee21644 doc: fix comment about non-existing CompareFeeFrac (Greg Sanders)

Pull request description:

  Follow-ups to https://github.com/bitcoin/bitcoin/pull/29242

ACKs for top commit:
  glozow:
    ACK ee1b9b231a0a7e89b77cbf8ea54e0534f0970dd0, reviewed the changes and package_rbf fuzzer seems to run fine
  murchandamus:
    crACK ee1b9b231a0a7e89b77cbf8ea54e0534f0970dd0
  ismaelsadeeq:
    Code review ACK ee1b9b231a0a7e89b77cbf8ea54e0534f0970dd0
  willcl-ark:
    ACK ee1b9b231a0a7e89b77cbf8ea54e0534f0970dd0

Tree-SHA512: 8399fe12064fb49b0e4c73258968b57be1d9c2e35701b2d3b0bb67e2e4052e44216358238f92508e4697d0fb6176518d5b885474054d3deda242f669e99262a7

6 files changed, 172 insertions, 98 deletions

diff --git a/src/policy/rbf.cpp b/src/policy/rbf.cpp
index a2c6990657..84c3352b9d 100644
--- a/src/policy/rbf.cpp
+++ b/src/policy/rbf.cpp
@@ -190,9 +190,7 @@ std::optional<std::pair<DiagramCheckError, std::string>> ImprovesFeerateDiagram(
                                                 CAmount replacement_fees,
                                                 int64_t replacement_vsize)
 {
-    // Require that the replacement strictly improve the mempool's feerate diagram.
-    std::vector<FeeFrac> old_diagram, new_diagram;
-
+    // Require that the replacement strictly improves the mempool's feerate diagram.
     const auto diagram_results{pool.CalculateFeerateDiagramsForRBF(replacement_fees, replacement_vsize, direct_conflicts, all_conflicts)};
 
     if (!diagram_results.has_value()) {
diff --git a/src/test/fuzz/rbf.cpp b/src/test/fuzz/rbf.cpp
index 42008c6ad9..754aff4e70 100644
--- a/src/test/fuzz/rbf.cpp
+++ b/src/test/fuzz/rbf.cpp
@@ -127,6 +127,10 @@ FUZZ_TARGET(package_rbf, .init = initialize_package_rbf)
         }
         mempool_txs.emplace_back(*child);
         pool.addUnchecked(ConsumeTxMemPoolEntry(fuzzed_data_provider, mempool_txs.back()));
+
+        if (fuzzed_data_provider.ConsumeBool()) {
+            pool.PrioritiseTransaction(mempool_txs.back().GetHash().ToUint256(), fuzzed_data_provider.ConsumeIntegralInRange<int32_t>(-100000, 100000));
+        }
     }
 
     // Pick some transactions at random to be the direct conflicts
@@ -174,5 +178,16 @@ FUZZ_TARGET(package_rbf, .init = initialize_package_rbf)
 
     // If internals report error, wrapper should too
     auto err_tuple{ImprovesFeerateDiagram(pool, direct_conflicts, all_conflicts, replacement_fees, replacement_vsize)};
-    if (!calc_results.has_value()) assert(err_tuple.has_value());
+    if (!calc_results.has_value()) {
+         assert(err_tuple.value().first == DiagramCheckError::UNCALCULABLE);
+    } else {
+        // Diagram check succeeded
+        if (!err_tuple.has_value()) {
+            // New diagram's final fee should always match or exceed old diagram's
+            assert(calc_results->first.back().fee <= calc_results->second.back().fee);
+        } else if (calc_results->first.back().fee > calc_results->second.back().fee) {
+            // Or it failed, and if old diagram had higher fees, it should be a failure
+            assert(err_tuple.value().first == DiagramCheckError::FAILURE);
+        }
+    }
 }
diff --git a/src/test/rbf_tests.cpp b/src/test/rbf_tests.cpp
index 961fd62fe4..ed33969710 100644
--- a/src/test/rbf_tests.cpp
+++ b/src/test/rbf_tests.cpp
@@ -37,6 +37,37 @@ static inline CTransactionRef make_tx(const std::vector<CTransactionRef>& inputs
     return MakeTransactionRef(tx);
 }
 
+// Make two child transactions from parent (which must have at least 2 outputs).
+// Each tx will have the same outputs, using the amounts specified in output_values.
+static inline std::pair<CTransactionRef, CTransactionRef> make_two_siblings(const CTransactionRef parent,
+                                      const std::vector<CAmount>& output_values)
+{
+    assert(parent->vout.size() >= 2);
+
+    // First tx takes first parent output
+    CMutableTransaction tx1 = CMutableTransaction();
+    tx1.vin.resize(1);
+    tx1.vout.resize(output_values.size());
+
+    tx1.vin[0].prevout.hash = parent->GetHash();
+    tx1.vin[0].prevout.n = 0;
+    // Add a witness so wtxid != txid
+    CScriptWitness witness;
+    witness.stack.emplace_back(10);
+    tx1.vin[0].scriptWitness = witness;
+
+    for (size_t i = 0; i < output_values.size(); ++i) {
+        tx1.vout[i].scriptPubKey = CScript() << OP_11 << OP_EQUAL;
+        tx1.vout[i].nValue = output_values[i];
+    }
+
+    // Second tx takes second parent output
+    CMutableTransaction tx2 = tx1;
+    tx2.vin[0].prevout.n = 1;
+
+    return std::make_pair(MakeTransactionRef(tx1), MakeTransactionRef(tx2));
+}
+
 static CTransactionRef add_descendants(const CTransactionRef& tx, int32_t num_descendants, CTxMemPool& pool)
     EXCLUSIVE_LOCKS_REQUIRED(::cs_main, pool.cs)
 {
@@ -67,6 +98,20 @@ static CTransactionRef add_descendant_to_parents(const std::vector<CTransactionR
     return child_tx;
 }
 
+// Makes two children for a single parent
+static std::pair<CTransactionRef, CTransactionRef> add_children_to_parent(const CTransactionRef parent, CTxMemPool& pool)
+    EXCLUSIVE_LOCKS_REQUIRED(::cs_main, pool.cs)
+{
+    AssertLockHeld(::cs_main);
+    AssertLockHeld(pool.cs);
+    TestMemPoolEntryHelper entry;
+    // Assumes this isn't already spent in mempool
+    auto children_tx = make_two_siblings(/*parent=*/parent, /*output_values=*/{50 * CENT});
+    pool.addUnchecked(entry.FromTx(children_tx.first));
+    pool.addUnchecked(entry.FromTx(children_tx.second));
+    return children_tx;
+}
+
 BOOST_FIXTURE_TEST_CASE(rbf_helper_functions, TestChain100Setup)
 {
     CTxMemPool& pool = *Assert(m_node.mempool);
@@ -116,6 +161,10 @@ BOOST_FIXTURE_TEST_CASE(rbf_helper_functions, TestChain100Setup)
     const auto tx12 = make_tx(/*inputs=*/ {m_coinbase_txns[8]}, /*output_values=*/ {995 * CENT});
     pool.addUnchecked(entry.Fee(normal_fee).FromTx(tx12));
 
+    // Will make two children of this single parent
+    const auto tx13 = make_tx(/*inputs=*/ {m_coinbase_txns[9]}, /*output_values=*/ {995 * CENT, 995 * CENT});
+    pool.addUnchecked(entry.Fee(normal_fee).FromTx(tx13));
+
     const auto entry1_normal = pool.GetIter(tx1->GetHash()).value();
     const auto entry2_normal = pool.GetIter(tx2->GetHash()).value();
     const auto entry3_low = pool.GetIter(tx3->GetHash()).value();
@@ -128,6 +177,7 @@ BOOST_FIXTURE_TEST_CASE(rbf_helper_functions, TestChain100Setup)
     const auto entry10_unchained = pool.GetIter(tx10->GetHash()).value();
     const auto entry11_unchained = pool.GetIter(tx11->GetHash()).value();
     const auto entry12_unchained = pool.GetIter(tx12->GetHash()).value();
+    const auto entry13_unchained = pool.GetIter(tx13->GetHash()).value();
 
     BOOST_CHECK_EQUAL(entry1_normal->GetFee(), normal_fee);
     BOOST_CHECK_EQUAL(entry2_normal->GetFee(), normal_fee);
@@ -261,7 +311,7 @@ BOOST_FIXTURE_TEST_CASE(rbf_helper_functions, TestChain100Setup)
     // Tests for CheckConflictTopology
 
     // Tx4 has 23 descendants
-    BOOST_CHECK(pool.CheckConflictTopology(set_34_cpfp).has_value());
+    BOOST_CHECK_EQUAL(pool.CheckConflictTopology(set_34_cpfp).value(), strprintf("%s has 23 descendants, max 1 allowed", entry4_high->GetSharedTx()->GetHash().ToString()));
 
     // No descendants yet
     BOOST_CHECK(pool.CheckConflictTopology({entry9_unchained}) == std::nullopt);
@@ -292,6 +342,14 @@ BOOST_FIXTURE_TEST_CASE(rbf_helper_functions, TestChain100Setup)
     BOOST_CHECK_EQUAL(pool.CheckConflictTopology({entry11_unchained}).value(), strprintf("%s is not the only parent of child %s", entry11_unchained->GetSharedTx()->GetHash().ToString(), entry_two_parent_child->GetSharedTx()->GetHash().ToString()));
     BOOST_CHECK_EQUAL(pool.CheckConflictTopology({entry12_unchained}).value(), strprintf("%s is not the only parent of child %s", entry12_unchained->GetSharedTx()->GetHash().ToString(), entry_two_parent_child->GetSharedTx()->GetHash().ToString()));
     BOOST_CHECK_EQUAL(pool.CheckConflictTopology({entry_two_parent_child}).value(), strprintf("%s has 2 ancestors, max 1 allowed", entry_two_parent_child->GetSharedTx()->GetHash().ToString()));
+
+    // Single parent with two children, we will conflict with the siblings directly only
+    const auto two_siblings = add_children_to_parent(tx13, pool);
+    const auto entry_sibling_1 = pool.GetIter(two_siblings.first->GetHash()).value();
+    const auto entry_sibling_2 = pool.GetIter(two_siblings.second->GetHash()).value();
+    BOOST_CHECK_EQUAL(pool.CheckConflictTopology({entry_sibling_1}).value(), strprintf("%s is not the only child of parent %s", entry_sibling_1->GetSharedTx()->GetHash().ToString(), entry13_unchained->GetSharedTx()->GetHash().ToString()));
+    BOOST_CHECK_EQUAL(pool.CheckConflictTopology({entry_sibling_2}).value(), strprintf("%s is not the only child of parent %s", entry_sibling_2->GetSharedTx()->GetHash().ToString(), entry13_unchained->GetSharedTx()->GetHash().ToString()));
+
 }
 
 BOOST_FIXTURE_TEST_CASE(improves_feerate, TestChain100Setup)
@@ -327,6 +385,17 @@ BOOST_FIXTURE_TEST_CASE(improves_feerate, TestChain100Setup)
     // With one more satoshi it does
     BOOST_CHECK(ImprovesFeerateDiagram(pool, {entry1}, {entry1, entry2}, tx1_fee + tx2_fee + 1, tx1_size + tx2_size) == std::nullopt);
 
+    // With prioritisation of in-mempool conflicts, it affects the results of the comparison using the same args as just above
+    pool.PrioritiseTransaction(entry1->GetSharedTx()->GetHash(), /*nFeeDelta=*/1);
+    const auto res2 = ImprovesFeerateDiagram(pool, {entry1}, {entry1, entry2}, tx1_fee + tx2_fee + 1, tx1_size + tx2_size);
+    BOOST_CHECK(res2.has_value());
+    BOOST_CHECK(res2.value().first == DiagramCheckError::FAILURE);
+    BOOST_CHECK(res2.value().second == "insufficient feerate: does not improve feerate diagram");
+    pool.PrioritiseTransaction(entry1->GetSharedTx()->GetHash(), /*nFeeDelta=*/-1);
+
+    // With one less vB it does
+    BOOST_CHECK(ImprovesFeerateDiagram(pool, {entry1}, {entry1, entry2}, tx1_fee + tx2_fee, tx1_size + tx2_size - 1) == std::nullopt);
+
     // Adding a grandchild makes the cluster size 3, which is uncalculable
     const auto tx3 = make_tx(/*inputs=*/ {tx2}, /*output_values=*/ {995 * CENT});
     pool.addUnchecked(entry.Fee(normal_fee).FromTx(tx3));
@@ -347,38 +416,33 @@ BOOST_FIXTURE_TEST_CASE(calc_feerate_diagram_rbf, TestChain100Setup)
     const CAmount normal_fee{CENT/10};
     const CAmount high_fee{CENT};
 
-    // low -> high -> medium fee transactions that would result in two chunks together
+    // low -> high -> medium fee transactions that would result in two chunks together since they
+    // are all same size
     const auto low_tx = make_tx(/*inputs=*/ {m_coinbase_txns[0]}, /*output_values=*/ {10 * COIN});
     pool.addUnchecked(entry.Fee(low_fee).FromTx(low_tx));
 
     const auto entry_low = pool.GetIter(low_tx->GetHash()).value();
     const auto low_size = entry_low->GetTxSize();
 
-    std::vector<FeeFrac> old_diagram, new_diagram;
-
     // Replacement of size 1
-    const auto replace_one{pool.CalculateFeerateDiagramsForRBF(/*replacement_fees=*/0, /*replacement_vsize=*/1, {entry_low}, {entry_low})};
-    BOOST_CHECK(replace_one.has_value());
-    old_diagram = replace_one->first;
-    new_diagram = replace_one->second;
-    BOOST_CHECK(old_diagram.size() == 2);
-    BOOST_CHECK(new_diagram.size() == 2);
-    BOOST_CHECK(old_diagram[0] == FeeFrac(0, 0));
-    BOOST_CHECK(old_diagram[1] == FeeFrac(low_fee, low_size));
-    BOOST_CHECK(new_diagram[0] == FeeFrac(0, 0));
-    BOOST_CHECK(new_diagram[1] == FeeFrac(0, 1));
+    {
+        const auto replace_one{pool.CalculateFeerateDiagramsForRBF(/*replacement_fees=*/0, /*replacement_vsize=*/1, {entry_low}, {entry_low})};
+        BOOST_CHECK(replace_one.has_value());
+        std::vector<FeeFrac> expected_old_diagram{FeeFrac(0, 0), FeeFrac(low_fee, low_size)};
+        BOOST_CHECK(replace_one->first == expected_old_diagram);
+        std::vector<FeeFrac> expected_new_diagram{FeeFrac(0, 0), FeeFrac(0, 1)};
+        BOOST_CHECK(replace_one->second == expected_new_diagram);
+    }
 
     // Non-zero replacement fee/size
-    const auto replace_one_fee{pool.CalculateFeerateDiagramsForRBF(/*replacement_fees=*/high_fee, /*replacement_vsize=*/low_size, {entry_low}, {entry_low})};
-    BOOST_CHECK(replace_one_fee.has_value());
-    old_diagram = replace_one_fee->first;
-    new_diagram = replace_one_fee->second;
-    BOOST_CHECK(old_diagram.size() == 2);
-    BOOST_CHECK(new_diagram.size() == 2);
-    BOOST_CHECK(old_diagram[0] == FeeFrac(0, 0));
-    BOOST_CHECK(old_diagram[1] == FeeFrac(low_fee, low_size));
-    BOOST_CHECK(new_diagram[0] == FeeFrac(0, 0));
-    BOOST_CHECK(new_diagram[1] == FeeFrac(high_fee, low_size));
+    {
+        const auto replace_one_fee{pool.CalculateFeerateDiagramsForRBF(/*replacement_fees=*/high_fee, /*replacement_vsize=*/low_size, {entry_low}, {entry_low})};
+        BOOST_CHECK(replace_one_fee.has_value());
+        std::vector<FeeFrac> expected_old_diagram{FeeFrac(0, 0), FeeFrac(low_fee, low_size)};
+        BOOST_CHECK(replace_one_fee->first == expected_old_diagram);
+        std::vector<FeeFrac> expected_new_diagram{FeeFrac(0, 0), FeeFrac(high_fee, low_size)};
+        BOOST_CHECK(replace_one_fee->second == expected_new_diagram);
+    }
 
     // Add a second transaction to the cluster that will make a single chunk, to be evicted in the RBF
     const auto high_tx = make_tx(/*inputs=*/ {low_tx}, /*output_values=*/ {995 * CENT});
@@ -386,29 +450,24 @@ BOOST_FIXTURE_TEST_CASE(calc_feerate_diagram_rbf, TestChain100Setup)
     const auto entry_high = pool.GetIter(high_tx->GetHash()).value();
     const auto high_size = entry_high->GetTxSize();
 
-    const auto replace_single_chunk{pool.CalculateFeerateDiagramsForRBF(/*replacement_fees=*/high_fee, /*replacement_vsize=*/low_size, {entry_low}, {entry_low, entry_high})};
-    BOOST_CHECK(replace_single_chunk.has_value());
-    old_diagram = replace_single_chunk->first;
-    new_diagram = replace_single_chunk->second;
-    BOOST_CHECK(old_diagram.size() == 2);
-    BOOST_CHECK(new_diagram.size() == 2);
-    BOOST_CHECK(old_diagram[0] == FeeFrac(0, 0));
-    BOOST_CHECK(old_diagram[1] == FeeFrac(low_fee + high_fee, low_size + high_size));
-    BOOST_CHECK(new_diagram[0] == FeeFrac(0, 0));
-    BOOST_CHECK(new_diagram[1] == FeeFrac(high_fee, low_size));
+    {
+        const auto replace_single_chunk{pool.CalculateFeerateDiagramsForRBF(/*replacement_fees=*/high_fee, /*replacement_vsize=*/low_size, {entry_low}, {entry_low, entry_high})};
+        BOOST_CHECK(replace_single_chunk.has_value());
+        std::vector<FeeFrac> expected_old_diagram{FeeFrac(0, 0), FeeFrac(low_fee + high_fee, low_size + high_size)};
+        BOOST_CHECK(replace_single_chunk->first == expected_old_diagram);
+        std::vector<FeeFrac> expected_new_diagram{FeeFrac(0, 0), FeeFrac(high_fee, low_size)};
+        BOOST_CHECK(replace_single_chunk->second == expected_new_diagram);
+    }
 
     // Conflict with the 2nd tx, resulting in new diagram with three entries
-    const auto replace_cpfp_child{pool.CalculateFeerateDiagramsForRBF(/*replacement_fees=*/high_fee, /*replacement_vsize=*/low_size, {entry_high}, {entry_high})};
-    BOOST_CHECK(replace_cpfp_child.has_value());
-    old_diagram = replace_cpfp_child->first;
-    new_diagram = replace_cpfp_child->second;
-    BOOST_CHECK(old_diagram.size() == 2);
-    BOOST_CHECK(new_diagram.size() == 3);
-    BOOST_CHECK(old_diagram[0] == FeeFrac(0, 0));
-    BOOST_CHECK(old_diagram[1] == FeeFrac(low_fee + high_fee, low_size + high_size));
-    BOOST_CHECK(new_diagram[0] == FeeFrac(0, 0));
-    BOOST_CHECK(new_diagram[1] == FeeFrac(high_fee, low_size));
-    BOOST_CHECK(new_diagram[2] == FeeFrac(low_fee + high_fee, low_size + low_size));
+    {
+        const auto replace_cpfp_child{pool.CalculateFeerateDiagramsForRBF(/*replacement_fees=*/high_fee, /*replacement_vsize=*/low_size, {entry_high}, {entry_high})};
+        BOOST_CHECK(replace_cpfp_child.has_value());
+        std::vector<FeeFrac> expected_old_diagram{FeeFrac(0, 0), FeeFrac(low_fee + high_fee, low_size + high_size)};
+        BOOST_CHECK(replace_cpfp_child->first == expected_old_diagram);
+        std::vector<FeeFrac> expected_new_diagram{FeeFrac(0, 0), FeeFrac(high_fee, low_size), FeeFrac(low_fee + high_fee, low_size + low_size)};
+        BOOST_CHECK(replace_cpfp_child->second == expected_new_diagram);
+    }
 
     // third transaction causes the topology check to fail
     const auto normal_tx = make_tx(/*inputs=*/ {high_tx}, /*output_values=*/ {995 * CENT});
@@ -416,11 +475,11 @@ BOOST_FIXTURE_TEST_CASE(calc_feerate_diagram_rbf, TestChain100Setup)
     const auto entry_normal = pool.GetIter(normal_tx->GetHash()).value();
     const auto normal_size = entry_normal->GetTxSize();
 
-    const auto replace_too_large{pool.CalculateFeerateDiagramsForRBF(/*replacement_fees=*/normal_fee, /*replacement_vsize=*/normal_size, {entry_low}, {entry_low, entry_high, entry_normal})};
-    BOOST_CHECK(!replace_too_large.has_value());
-    BOOST_CHECK_EQUAL(util::ErrorString(replace_too_large).original, strprintf("%s has 2 descendants, max 1 allowed", low_tx->GetHash().GetHex()));
-    old_diagram.clear();
-    new_diagram.clear();
+    {
+        const auto replace_too_large{pool.CalculateFeerateDiagramsForRBF(/*replacement_fees=*/normal_fee, /*replacement_vsize=*/normal_size, {entry_low}, {entry_low, entry_high, entry_normal})};
+        BOOST_CHECK(!replace_too_large.has_value());
+        BOOST_CHECK_EQUAL(util::ErrorString(replace_too_large).original, strprintf("%s has 2 descendants, max 1 allowed", low_tx->GetHash().GetHex()));
+    }
 
     // Make a size 2 cluster that is itself two chunks; evict both txns
     const auto high_tx_2 = make_tx(/*inputs=*/ {m_coinbase_txns[1]}, /*output_values=*/ {10 * COIN});
@@ -433,19 +492,16 @@ BOOST_FIXTURE_TEST_CASE(calc_feerate_diagram_rbf, TestChain100Setup)
     const auto entry_low_2 = pool.GetIter(low_tx_2->GetHash()).value();
     const auto low_size_2 = entry_low_2->GetTxSize();
 
-    const auto replace_two_chunks_single_cluster{pool.CalculateFeerateDiagramsForRBF(/*replacement_fees=*/high_fee, /*replacement_vsize=*/low_size, {entry_high_2}, {entry_high_2, entry_low_2})};
-    BOOST_CHECK(replace_two_chunks_single_cluster.has_value());
-    old_diagram = replace_two_chunks_single_cluster->first;
-    new_diagram = replace_two_chunks_single_cluster->second;
-    BOOST_CHECK(old_diagram.size() == 3);
-    BOOST_CHECK(new_diagram.size() == 2);
-    BOOST_CHECK(old_diagram[0] == FeeFrac(0, 0));
-    BOOST_CHECK(old_diagram[1] == FeeFrac(high_fee, high_size_2));
-    BOOST_CHECK(old_diagram[2] == FeeFrac(low_fee + high_fee, low_size_2 + high_size_2));
-    BOOST_CHECK(new_diagram[0] == FeeFrac(0, 0));
-    BOOST_CHECK(new_diagram[1] == FeeFrac(high_fee, low_size_2));
-
-    // You can have more than two direct conflicts if the there are multiple effected clusters, all of size 2 or less
+    {
+        const auto replace_two_chunks_single_cluster{pool.CalculateFeerateDiagramsForRBF(/*replacement_fees=*/high_fee, /*replacement_vsize=*/low_size, {entry_high_2}, {entry_high_2, entry_low_2})};
+        BOOST_CHECK(replace_two_chunks_single_cluster.has_value());
+        std::vector<FeeFrac> expected_old_diagram{FeeFrac(0, 0), FeeFrac(high_fee, high_size_2), FeeFrac(low_fee + high_fee, low_size_2 + high_size_2)};
+        BOOST_CHECK(replace_two_chunks_single_cluster->first == expected_old_diagram);
+        std::vector<FeeFrac> expected_new_diagram{FeeFrac(0, 0), FeeFrac(high_fee, low_size_2)};
+        BOOST_CHECK(replace_two_chunks_single_cluster->second == expected_new_diagram);
+    }
+
+    // You can have more than two direct conflicts if the there are multiple affected clusters, all of size 2 or less
     const auto conflict_1 = make_tx(/*inputs=*/ {m_coinbase_txns[2]}, /*output_values=*/ {10 * COIN});
     pool.addUnchecked(entry.Fee(low_fee).FromTx(conflict_1));
     const auto conflict_1_entry = pool.GetIter(conflict_1->GetHash()).value();
@@ -458,40 +514,37 @@ BOOST_FIXTURE_TEST_CASE(calc_feerate_diagram_rbf, TestChain100Setup)
     pool.addUnchecked(entry.Fee(low_fee).FromTx(conflict_3));
     const auto conflict_3_entry = pool.GetIter(conflict_3->GetHash()).value();
 
-    const auto replace_multiple_clusters{pool.CalculateFeerateDiagramsForRBF(/*replacement_fees=*/high_fee, /*replacement_vsize=*/low_size, {conflict_1_entry, conflict_2_entry, conflict_3_entry}, {conflict_1_entry, conflict_2_entry, conflict_3_entry})};
-
-    BOOST_CHECK(replace_multiple_clusters.has_value());
-    old_diagram = replace_multiple_clusters->first;
-    new_diagram = replace_multiple_clusters->second;
-    BOOST_CHECK(old_diagram.size() == 4);
-    BOOST_CHECK(new_diagram.size() == 2);
+    {
+        const auto replace_multiple_clusters{pool.CalculateFeerateDiagramsForRBF(/*replacement_fees=*/high_fee, /*replacement_vsize=*/low_size, {conflict_1_entry, conflict_2_entry, conflict_3_entry}, {conflict_1_entry, conflict_2_entry, conflict_3_entry})};
+        BOOST_CHECK(replace_multiple_clusters.has_value());
+        BOOST_CHECK(replace_multiple_clusters->first.size() == 4);
+        BOOST_CHECK(replace_multiple_clusters->second.size() == 2);
+    }
 
-    // Add a child transaction to conflict_1 and make it cluster size 2, still one chunk due to same feerate
+    // Add a child transaction to conflict_1 and make it cluster size 2, two chunks due to same feerate
     const auto conflict_1_child = make_tx(/*inputs=*/{conflict_1}, /*output_values=*/ {995 * CENT});
     pool.addUnchecked(entry.Fee(low_fee).FromTx(conflict_1_child));
     const auto conflict_1_child_entry = pool.GetIter(conflict_1_child->GetHash()).value();
 
-    const auto replace_multiple_clusters_2{pool.CalculateFeerateDiagramsForRBF(/*replacement_fees=*/high_fee, /*replacement_vsize=*/low_size, {conflict_1_entry, conflict_2_entry, conflict_3_entry}, {conflict_1_entry, conflict_2_entry, conflict_3_entry, conflict_1_child_entry})};
+    {
+        const auto replace_multiple_clusters_2{pool.CalculateFeerateDiagramsForRBF(/*replacement_fees=*/high_fee, /*replacement_vsize=*/low_size, {conflict_1_entry, conflict_2_entry, conflict_3_entry}, {conflict_1_entry, conflict_2_entry, conflict_3_entry, conflict_1_child_entry})};
 
-    BOOST_CHECK(replace_multiple_clusters_2.has_value());
-    old_diagram = replace_multiple_clusters_2->first;
-    new_diagram = replace_multiple_clusters_2->second;
-    BOOST_CHECK(old_diagram.size() == 4);
-    BOOST_CHECK(new_diagram.size() == 2);
-    old_diagram.clear();
-    new_diagram.clear();
+        BOOST_CHECK(replace_multiple_clusters_2.has_value());
+        BOOST_CHECK(replace_multiple_clusters_2->first.size() == 5);
+        BOOST_CHECK(replace_multiple_clusters_2->second.size() == 2);
+    }
 
     // Add another descendant to conflict_1, making the cluster size > 2 should fail at this point.
     const auto conflict_1_grand_child = make_tx(/*inputs=*/{conflict_1_child}, /*output_values=*/ {995 * CENT});
     pool.addUnchecked(entry.Fee(high_fee).FromTx(conflict_1_grand_child));
     const auto conflict_1_grand_child_entry = pool.GetIter(conflict_1_child->GetHash()).value();
 
-    const auto replace_cluster_size_3{pool.CalculateFeerateDiagramsForRBF(/*replacement_fees=*/high_fee, /*replacement_vsize=*/low_size, {conflict_1_entry, conflict_2_entry, conflict_3_entry}, {conflict_1_entry, conflict_2_entry, conflict_3_entry, conflict_1_child_entry, conflict_1_grand_child_entry})};
+    {
+        const auto replace_cluster_size_3{pool.CalculateFeerateDiagramsForRBF(/*replacement_fees=*/high_fee, /*replacement_vsize=*/low_size, {conflict_1_entry, conflict_2_entry, conflict_3_entry}, {conflict_1_entry, conflict_2_entry, conflict_3_entry, conflict_1_child_entry, conflict_1_grand_child_entry})};
 
-    BOOST_CHECK(!replace_cluster_size_3.has_value());
-    BOOST_CHECK_EQUAL(util::ErrorString(replace_cluster_size_3).original, strprintf("%s has 2 descendants, max 1 allowed", conflict_1->GetHash().GetHex()));
-    BOOST_CHECK(old_diagram.empty());
-    BOOST_CHECK(new_diagram.empty());
+        BOOST_CHECK(!replace_cluster_size_3.has_value());
+        BOOST_CHECK_EQUAL(util::ErrorString(replace_cluster_size_3).original, strprintf("%s has 2 descendants, max 1 allowed", conflict_1->GetHash().GetHex()));
+    }
 }
 
 BOOST_AUTO_TEST_CASE(feerate_diagram_utilities)
@@ -503,18 +556,21 @@ BOOST_AUTO_TEST_CASE(feerate_diagram_utilities)
     std::vector<FeeFrac> new_diagram{{FeeFrac{0, 0}, FeeFrac{1000, 300}, FeeFrac{1050, 400}}};
 
     BOOST_CHECK(std::is_lt(CompareFeerateDiagram(old_diagram, new_diagram)));
+    BOOST_CHECK(std::is_gt(CompareFeerateDiagram(new_diagram, old_diagram)));
 
     // Incomparable diagrams
     old_diagram = {FeeFrac{0, 0}, FeeFrac{950, 300}, FeeFrac{1050, 400}};
     new_diagram = {FeeFrac{0, 0}, FeeFrac{1000, 300}, FeeFrac{1000, 400}};
 
     BOOST_CHECK(CompareFeerateDiagram(old_diagram, new_diagram) == std::partial_ordering::unordered);
+    BOOST_CHECK(CompareFeerateDiagram(new_diagram, old_diagram) == std::partial_ordering::unordered);
 
     // Strictly better but smaller size.
     old_diagram = {FeeFrac{0, 0}, FeeFrac{950, 300}, FeeFrac{1050, 400}};
     new_diagram = {FeeFrac{0, 0}, FeeFrac{1100, 300}};
 
     BOOST_CHECK(std::is_lt(CompareFeerateDiagram(old_diagram, new_diagram)));
+    BOOST_CHECK(std::is_gt(CompareFeerateDiagram(new_diagram, old_diagram)));
 
     // New diagram is strictly better due to the first chunk, even though
     // second chunk contributes no fees
@@ -522,24 +578,28 @@ BOOST_AUTO_TEST_CASE(feerate_diagram_utilities)
     new_diagram = {FeeFrac{0, 0}, FeeFrac{1100, 100}, FeeFrac{1100, 200}};
 
     BOOST_CHECK(std::is_lt(CompareFeerateDiagram(old_diagram, new_diagram)));
+    BOOST_CHECK(std::is_gt(CompareFeerateDiagram(new_diagram, old_diagram)));
 
     // Feerate of first new chunk is better with, but second chunk is worse
     old_diagram = {FeeFrac{0, 0}, FeeFrac{950, 300}, FeeFrac{1050, 400}};
     new_diagram = {FeeFrac{0, 0}, FeeFrac{750, 100}, FeeFrac{999, 350}, FeeFrac{1150, 1000}};
 
     BOOST_CHECK(CompareFeerateDiagram(old_diagram, new_diagram) == std::partial_ordering::unordered);
+    BOOST_CHECK(CompareFeerateDiagram(new_diagram, old_diagram) == std::partial_ordering::unordered);
 
     // If we make the second chunk slightly better, the new diagram now wins.
     old_diagram = {FeeFrac{0, 0}, FeeFrac{950, 300}, FeeFrac{1050, 400}};
     new_diagram = {FeeFrac{0, 0}, FeeFrac{750, 100}, FeeFrac{1000, 350}, FeeFrac{1150, 500}};
 
     BOOST_CHECK(std::is_lt(CompareFeerateDiagram(old_diagram, new_diagram)));
+    BOOST_CHECK(std::is_gt(CompareFeerateDiagram(new_diagram, old_diagram)));
 
     // Identical diagrams, cannot be strictly better
     old_diagram = {FeeFrac{0, 0}, FeeFrac{950, 300}, FeeFrac{1050, 400}};
     new_diagram = {FeeFrac{0, 0}, FeeFrac{950, 300}, FeeFrac{1050, 400}};
 
     BOOST_CHECK(std::is_eq(CompareFeerateDiagram(old_diagram, new_diagram)));
+    BOOST_CHECK(std::is_eq(CompareFeerateDiagram(new_diagram, old_diagram)));
 
     // Same aggregate fee, but different total size (trigger single tail fee check step)
     old_diagram = {FeeFrac{0, 0}, FeeFrac{950, 300}, FeeFrac{1050, 399}};
@@ -547,8 +607,6 @@ BOOST_AUTO_TEST_CASE(feerate_diagram_utilities)
 
     // No change in evaluation when tail check needed.
     BOOST_CHECK(std::is_gt(CompareFeerateDiagram(old_diagram, new_diagram)));
-
-    // Padding works on either argument
     BOOST_CHECK(std::is_lt(CompareFeerateDiagram(new_diagram, old_diagram)));
 
     // Trigger multiple tail fee check steps
@@ -561,6 +619,7 @@ BOOST_AUTO_TEST_CASE(feerate_diagram_utilities)
     // Multiple tail fee check steps, unordered result
     new_diagram = {FeeFrac{0, 0}, FeeFrac{950, 300}, FeeFrac{1050, 400}, FeeFrac{1050, 401}, FeeFrac{1050, 402}, FeeFrac{1051, 403}};
     BOOST_CHECK(CompareFeerateDiagram(old_diagram, new_diagram) == std::partial_ordering::unordered);
+    BOOST_CHECK(CompareFeerateDiagram(new_diagram, old_diagram) == std::partial_ordering::unordered);
 }
 
 BOOST_AUTO_TEST_SUITE_END()
diff --git a/src/txmempool.cpp b/src/txmempool.cpp
index 4047ceda3c..82eec6241f 100644
--- a/src/txmempool.cpp
+++ b/src/txmempool.cpp
@@ -1294,9 +1294,10 @@ util::Result<std::pair<std::vector<FeeFrac>, std::vector<FeeFrac>>> CTxMemPool::
     // direct_conflicts that is at its own fee/size, along with the replacement
     // tx/package at its own fee/size
 
-    // old diagram will consist of each element of all_conflicts either at
-    // its own feerate (followed by any descendant at its own feerate) or as a
-    // single chunk at its descendant's ancestor feerate.
+    // old diagram will consist of the ancestors and descendants of each element of
+    // all_conflicts.  every such transaction will either be at its own feerate (followed
+    // by any descendant at its own feerate), or as a single chunk at the descendant's
+    // ancestor feerate.
 
     std::vector<FeeFrac> old_chunks;
     // Step 1: build the old diagram.
@@ -1317,7 +1318,7 @@ util::Result<std::pair<std::vector<FeeFrac>, std::vector<FeeFrac>>> CTxMemPool::
             // We'll add chunks for either the ancestor by itself and this tx
             // by itself, or for a combined package.
             FeeFrac package{txiter->GetModFeesWithAncestors(), static_cast<int32_t>(txiter->GetSizeWithAncestors())};
-            if (individual > package) {
+            if (individual >> package) {
                 // The individual feerate is higher than the package, and
                 // therefore higher than the parent's fee. Chunk these
                 // together.
diff --git a/src/util/feefrac.cpp b/src/util/feefrac.cpp
index a271fe585e..68fb836936 100644
--- a/src/util/feefrac.cpp
+++ b/src/util/feefrac.cpp
@@ -53,7 +53,6 @@ std::partial_ordering CompareFeerateDiagram(Span<const FeeFrac> dia0, Span<const
         const FeeFrac& point_p = next_point(unproc_side);
         const FeeFrac& point_a = prev_point(!unproc_side);
 
-        // Slope of AP can be negative, unlike AB
         const auto slope_ap = point_p - point_a;
         Assume(slope_ap.size > 0);
         std::weak_ordering cmp = std::weak_ordering::equivalent;
@@ -77,10 +76,12 @@ std::partial_ordering CompareFeerateDiagram(Span<const FeeFrac> dia0, Span<const
         if (std::is_gt(cmp)) better_somewhere[unproc_side] = true;
         if (std::is_lt(cmp)) better_somewhere[!unproc_side] = true;
         ++next_index[unproc_side];
+
+        // If both diagrams are better somewhere, they are incomparable.
+        if (better_somewhere[0] && better_somewhere[1]) return std::partial_ordering::unordered;
+
     } while(true);
 
-    // If both diagrams are better somewhere, they are incomparable.
-    if (better_somewhere[0] && better_somewhere[1]) return std::partial_ordering::unordered;
     // Otherwise compare the better_somewhere values.
     return better_somewhere[0] <=> better_somewhere[1];
 }
diff --git a/src/util/feefrac.h b/src/util/feefrac.h
index 48bd287c7c..7102f85f88 100644
--- a/src/util/feefrac.h
+++ b/src/util/feefrac.h
@@ -31,7 +31,7 @@
  * A FeeFrac is considered "better" if it sorts after another, by this ordering. All standard
  * comparison operators (<=>, ==, !=, >, <, >=, <=) respect this ordering.
  *
- * The CompareFeeFrac, and >> and << operators only compare feerate and treat equal feerate but
+ * The FeeRateCompare, and >> and << operators only compare feerate and treat equal feerate but
  * different size as equivalent. The empty FeeFrac is neither lower or higher in feerate than any
  * other.
  */