Merge #12118: Sort mempool by min(feerate, ancestor_feerate)

0a22a52 Use mempool's ancestor sort in transaction selection (Suhas Daftuar)
7abfa53 Add test for new ancestor feerate sort behavior (Suhas Daftuar)
9a51319 Sort mempool by min(feerate, ancestor_feerate) (Suhas Daftuar)
6773f92 Refactor CompareTxMemPoolEntryByDescendantScore (Suhas Daftuar)

Pull request description:

  This more closely approximates the desirability of a given transaction for
  mining, and should result in less re-sorting when transactions get removed from
  the mempool after being mined.

  I measured this as approximately a 5% speedup in removeForBlock.

Tree-SHA512: ffa36b567c5dfe3e8908c545a459b6a5ec0de26e7dc81b1050dd235cac9046564b4409a3f8c5ba97bd8b30526e8fec8f78480a912e317979467f32305c3dd37b

src/miner.cpp

@@ -410,7 +410,7 @@ void BlockAssembler::addPackageTxs(int &nPackagesSelected, int &nDescendantsUpda
             // Try to compare the mapTx entry to the mapModifiedTx entry
             iter = mempool.mapTx.project<0>(mi);
             if (modit != mapModifiedTx.get<ancestor_score>().end() &&
-                    CompareModifiedEntry()(*modit, CTxMemPoolModifiedEntry(iter))) {
+                    CompareTxMemPoolEntryByAncestorFee()(*modit, CTxMemPoolModifiedEntry(iter))) {
                 // The best entry in mapModifiedTx has higher score
                 // than the one from mapTx.
                 // Switch which transaction (package) to consider

src/miner.h

@@ -44,6 +44,12 @@ struct CTxMemPoolModifiedEntry {
         nSigOpCountWithAncestors = entry->GetSigOpCountWithAncestors();
     }
 
+    int64_t GetModifiedFee() const { return iter->GetModifiedFee(); }
+    uint64_t GetSizeWithAncestors() const { return nSizeWithAncestors; }
+    CAmount GetModFeesWithAncestors() const { return nModFeesWithAncestors; }
+    size_t GetTxSize() const { return iter->GetTxSize(); }
+    const CTransaction& GetTx() const { return iter->GetTx(); }
+
     CTxMemPool::txiter iter;
     uint64_t nSizeWithAncestors;
     CAmount nModFeesWithAncestors;
@@ -70,21 +76,6 @@ struct modifiedentry_iter {
     }
 };
 
-// This matches the calculation in CompareTxMemPoolEntryByAncestorFee,
-// except operating on CTxMemPoolModifiedEntry.
-// TODO: refactor to avoid duplication of this logic.
-struct CompareModifiedEntry {
-    bool operator()(const CTxMemPoolModifiedEntry &a, const CTxMemPoolModifiedEntry &b) const
-    {
-        double f1 = (double)a.nModFeesWithAncestors * b.nSizeWithAncestors;
-        double f2 = (double)b.nModFeesWithAncestors * a.nSizeWithAncestors;
-        if (f1 == f2) {
-            return CTxMemPool::CompareIteratorByHash()(a.iter, b.iter);
-        }
-        return f1 > f2;
-    }
-};
-
 // A comparator that sorts transactions based on number of ancestors.
 // This is sufficient to sort an ancestor package in an order that is valid
 // to appear in a block.
@@ -109,7 +100,7 @@ typedef boost::multi_index_container<
             // Reuse same tag from CTxMemPool's similar index
             boost::multi_index::tag<ancestor_score>,
             boost::multi_index::identity<CTxMemPoolModifiedEntry>,
-            CompareModifiedEntry
+            CompareTxMemPoolEntryByAncestorFee
         >
     >
 > indexed_modified_transaction_set;

src/test/mempool_tests.cpp

@@ -397,6 +397,23 @@ BOOST_AUTO_TEST_CASE(MempoolAncestorIndexingTest)
         sortedOrder.erase(sortedOrder.end()-2);
     sortedOrder.insert(sortedOrder.begin(), tx7.GetHash().ToString());
     CheckSort<ancestor_score>(pool, sortedOrder);
+
+    // High-fee parent, low-fee child
+    // tx7 -> tx8
+    CMutableTransaction tx8 = CMutableTransaction();
+    tx8.vin.resize(1);
+    tx8.vin[0].prevout  = COutPoint(tx7.GetHash(), 0);
+    tx8.vin[0].scriptSig = CScript() << OP_11;
+    tx8.vout.resize(1);
+    tx8.vout[0].scriptPubKey = CScript() << OP_11 << OP_EQUAL;
+    tx8.vout[0].nValue = 10*COIN;
+
+    // Check that we sort by min(feerate, ancestor_feerate):
+    // set the fee so that the ancestor feerate is above tx1/5,
+    // but the transaction's own feerate is lower
+    pool.addUnchecked(tx8.GetHash(), entry.Fee(5000LL).FromTx(tx8));
+    sortedOrder.insert(sortedOrder.end()-1, tx8.GetHash().ToString());
+    CheckSort<ancestor_score>(pool, sortedOrder);
 }
 
 

src/txmempool.h

@@ -214,18 +214,14 @@ class CompareTxMemPoolEntryByDescendantScore
 public:
     bool operator()(const CTxMemPoolEntry& a, const CTxMemPoolEntry& b) const
     {
-        bool fUseADescendants = UseDescendantScore(a);
+        double a_mod_fee, a_size, b_mod_fee, b_size;
-        bool fUseBDescendants = UseDescendantScore(b);
 
-        double aModFee = fUseADescendants ? a.GetModFeesWithDescendants() : a.GetModifiedFee();
+        GetModFeeAndSize(a, a_mod_fee, a_size);
-        double aSize = fUseADescendants ? a.GetSizeWithDescendants() : a.GetTxSize();
+        GetModFeeAndSize(b, b_mod_fee, b_size);
-
-        double bModFee = fUseBDescendants ? b.GetModFeesWithDescendants() : b.GetModifiedFee();
-        double bSize = fUseBDescendants ? b.GetSizeWithDescendants() : b.GetTxSize();
 
         // Avoid division by rewriting (a/b > c/d) as (a*d > c*b).
-        double f1 = aModFee * bSize;
+        double f1 = a_mod_fee * b_size;
-        double f2 = aSize * bModFee;
+        double f2 = a_size * b_mod_fee;
 
         if (f1 == f2) {
             return a.GetTime() >= b.GetTime();
@@ -233,12 +229,21 @@ public:
         return f1 < f2;
     }
 
-    // Calculate which score to use for an entry (avoiding division).
+    // Return the fee/size we're using for sorting this entry.
-    bool UseDescendantScore(const CTxMemPoolEntry &a) const
+    void GetModFeeAndSize(const CTxMemPoolEntry &a, double &mod_fee, double &size) const
     {
+        // Compare feerate with descendants to feerate of the transaction, and
+        // return the fee/size for the max.
         double f1 = (double)a.GetModifiedFee() * a.GetSizeWithDescendants();
         double f2 = (double)a.GetModFeesWithDescendants() * a.GetTxSize();
-        return f2 > f1;
+
+        if (f2 > f1) {
+            mod_fee = a.GetModFeesWithDescendants();
+            size = a.GetSizeWithDescendants();
+        } else {
+            mod_fee = a.GetModifiedFee();
+            size = a.GetTxSize();
+        }
     }
 };
 
@@ -269,27 +274,48 @@ public:
     }
 };
 
+/** \class CompareTxMemPoolEntryByAncestorScore
+ *
+ *  Sort an entry by min(score/size of entry's tx, score/size with all ancestors).
+ */
 class CompareTxMemPoolEntryByAncestorFee
 {
 public:
-    bool operator()(const CTxMemPoolEntry& a, const CTxMemPoolEntry& b) const
+    template<typename T>
+    bool operator()(const T& a, const T& b) const
     {
-        double aFees = a.GetModFeesWithAncestors();
+        double a_mod_fee, a_size, b_mod_fee, b_size;
-        double aSize = a.GetSizeWithAncestors();
 
-        double bFees = b.GetModFeesWithAncestors();
+        GetModFeeAndSize(a, a_mod_fee, a_size);
-        double bSize = b.GetSizeWithAncestors();
+        GetModFeeAndSize(b, b_mod_fee, b_size);
 
         // Avoid division by rewriting (a/b > c/d) as (a*d > c*b).
-        double f1 = aFees * bSize;
+        double f1 = a_mod_fee * b_size;
-        double f2 = aSize * bFees;
+        double f2 = a_size * b_mod_fee;
 
         if (f1 == f2) {
             return a.GetTx().GetHash() < b.GetTx().GetHash();
         }
-
         return f1 > f2;
     }
+
+    // Return the fee/size we're using for sorting this entry.
+    template <typename T>
+    void GetModFeeAndSize(const T &a, double &mod_fee, double &size) const
+    {
+        // Compare feerate with ancestors to feerate of the transaction, and
+        // return the fee/size for the min.
+        double f1 = (double)a.GetModifiedFee() * a.GetSizeWithAncestors();
+        double f2 = (double)a.GetModFeesWithAncestors() * a.GetTxSize();
+
+        if (f1 > f2) {
+            mod_fee = a.GetModFeesWithAncestors();
+            size = a.GetSizeWithAncestors();
+        } else {
+            mod_fee = a.GetModifiedFee();
+            size = a.GetTxSize();
+        }
+    }
 };
 
 // Multi_index tag names