Use ancestor-feerate based transaction selection for mining

Includes changes by Pieter Wuille

src/miner.cpp

@@ -25,6 +25,7 @@
 #include "utilmoneystr.h"
 #include "validationinterface.h"
 
+#include <algorithm>
 #include <boost/thread.hpp>
 #include <boost/tuple/tuple.hpp>
 #include <queue>
@@ -134,7 +135,7 @@ CBlockTemplate* BlockAssembler::CreateNewBlock(const CScript& scriptPubKeyIn)
                        : pblock->GetBlockTime();
 
     addPriorityTxs();
-    addScoreTxs();
+    addPackageTxs();
 
     nLastBlockTx = nBlockTx;
     nLastBlockSize = nBlockSize;
@@ -177,7 +178,38 @@ bool BlockAssembler::isStillDependent(CTxMemPool::txiter iter)
     return false;
 }
 
+void BlockAssembler::onlyUnconfirmed(CTxMemPool::setEntries& testSet)
+{
+    for (CTxMemPool::setEntries::iterator iit = testSet.begin(); iit != testSet.end(); ) {
+        // Only test txs not already in the block
+        if (inBlock.count(*iit)) {
+            testSet.erase(iit++);
+        }
+        else {
+            iit++;
+        }
+    }
+}
 
+bool BlockAssembler::TestPackage(uint64_t packageSize, unsigned int packageSigOps)
+{
+    if (nBlockSize + packageSize >= nBlockMaxSize)
+        return false;
+    if (nBlockSigOps + packageSigOps >= MAX_BLOCK_SIGOPS)
+        return false;
+    return true;
+}
+
+// Block size and sigops have already been tested.  Check that all transactions
+// are final.
+bool BlockAssembler::TestPackageFinality(const CTxMemPool::setEntries& package)
+{
+    BOOST_FOREACH (const CTxMemPool::txiter it, package) {
+        if (!IsFinalTx(it->GetTx(), nHeight, nLockTimeCutoff))
+            return false;
+    }
+    return true;
+}
 
 bool BlockAssembler::TestForBlock(CTxMemPool::txiter iter)
 {
@@ -297,6 +329,178 @@ void BlockAssembler::addScoreTxs()
     }
 }
 
+void BlockAssembler::UpdatePackagesForAdded(const CTxMemPool::setEntries& alreadyAdded,
+        indexed_modified_transaction_set &mapModifiedTx)
+{
+    BOOST_FOREACH(const CTxMemPool::txiter it, alreadyAdded) {
+        CTxMemPool::setEntries descendants;
+        mempool.CalculateDescendants(it, descendants);
+        // Insert all descendants (not yet in block) into the modified set
+        BOOST_FOREACH(CTxMemPool::txiter desc, descendants) {
+            if (alreadyAdded.count(desc))
+                continue;
+            modtxiter mit = mapModifiedTx.find(desc);
+            if (mit == mapModifiedTx.end()) {
+                CTxMemPoolModifiedEntry modEntry(desc);
+                modEntry.nSizeWithAncestors -= it->GetTxSize();
+                modEntry.nModFeesWithAncestors -= it->GetModifiedFee();
+                modEntry.nSigOpCountWithAncestors -= it->GetSigOpCount();
+                mapModifiedTx.insert(modEntry);
+            } else {
+                mapModifiedTx.modify(mit, update_for_parent_inclusion(it));
+            }
+        }
+    }
+}
+
+// Skip entries in mapTx that are already in a block or are present
+// in mapModifiedTx (which implies that the mapTx ancestor state is
+// stale due to ancestor inclusion in the block)
+// Also skip transactions that we've already failed to add. This can happen if
+// we consider a transaction in mapModifiedTx and it fails: we can then
+// potentially consider it again while walking mapTx.  It's currently
+// guaranteed to fail again, but as a belt-and-suspenders check we put it in
+// failedTx and avoid re-evaluation, since the re-evaluation would be using
+// cached size/sigops/fee values that are not actually correct.
+bool BlockAssembler::SkipMapTxEntry(CTxMemPool::txiter it, indexed_modified_transaction_set &mapModifiedTx, CTxMemPool::setEntries &failedTx)
+{
+    assert (it != mempool.mapTx.end());
+    if (mapModifiedTx.count(it) || inBlock.count(it) || failedTx.count(it))
+        return true;
+    return false;
+}
+
+void BlockAssembler::SortForBlock(const CTxMemPool::setEntries& package, CTxMemPool::txiter entry, std::vector<CTxMemPool::txiter>& sortedEntries)
+{
+    // Sort package by ancestor count
+    // If a transaction A depends on transaction B, then A's ancestor count
+    // must be greater than B's.  So this is sufficient to validly order the
+    // transactions for block inclusion.
+    sortedEntries.clear();
+    sortedEntries.insert(sortedEntries.begin(), package.begin(), package.end());
+    std::sort(sortedEntries.begin(), sortedEntries.end(), CompareTxIterByAncestorCount());
+}
+
+// This transaction selection algorithm orders the mempool based
+// on feerate of a transaction including all unconfirmed ancestors.
+// Since we don't remove transactions from the mempool as we select them
+// for block inclusion, we need an alternate method of updating the feerate
+// of a transaction with its not-yet-selected ancestors as we go.
+// This is accomplished by walking the in-mempool descendants of selected
+// transactions and storing a temporary modified state in mapModifiedTxs.
+// Each time through the loop, we compare the best transaction in
+// mapModifiedTxs with the next transaction in the mempool to decide what
+// transaction package to work on next.
+void BlockAssembler::addPackageTxs()
+{
+    // mapModifiedTx will store sorted packages after they are modified
+    // because some of their txs are already in the block
+    indexed_modified_transaction_set mapModifiedTx;
+    // Keep track of entries that failed inclusion, to avoid duplicate work
+    CTxMemPool::setEntries failedTx;
+
+    // Start by adding all descendants of previously added txs to mapModifiedTx
+    // and modifying them for their already included ancestors
+    UpdatePackagesForAdded(inBlock, mapModifiedTx);
+
+    CTxMemPool::indexed_transaction_set::index<ancestor_score>::type::iterator mi = mempool.mapTx.get<ancestor_score>().begin();
+    CTxMemPool::txiter iter;
+    while (mi != mempool.mapTx.get<ancestor_score>().end() || !mapModifiedTx.empty())
+    {
+        // First try to find a new transaction in mapTx to evaluate.
+        if (mi != mempool.mapTx.get<ancestor_score>().end() &&
+                SkipMapTxEntry(mempool.mapTx.project<0>(mi), mapModifiedTx, failedTx)) {
+            ++mi;
+            continue;
+        }
+
+        // Now that mi is not stale, determine which transaction to evaluate:
+        // the next entry from mapTx, or the best from mapModifiedTx?
+        bool fUsingModified = false;
+
+        modtxscoreiter modit = mapModifiedTx.get<ancestor_score>().begin();
+        if (mi == mempool.mapTx.get<ancestor_score>().end()) {
+            // We're out of entries in mapTx; use the entry from mapModifiedTx
+            iter = modit->iter;
+            fUsingModified = true;
+        } else {
+            // 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))) {
+                // The best entry in mapModifiedTx has higher score
+                // than the one from mapTx.
+                // Switch which transaction (package) to consider
+                iter = modit->iter;
+                fUsingModified = true;
+            } else {
+                // Either no entry in mapModifiedTx, or it's worse than mapTx.
+                // Increment mi for the next loop iteration.
+                ++mi;
+            }
+        }
+
+        // We skip mapTx entries that are inBlock, and mapModifiedTx shouldn't
+        // contain anything that is inBlock.
+        assert(!inBlock.count(iter));
+
+        uint64_t packageSize = iter->GetSizeWithAncestors();
+        CAmount packageFees = iter->GetModFeesWithAncestors();
+        unsigned int packageSigOps = iter->GetSigOpCountWithAncestors();
+        if (fUsingModified) {
+            packageSize = modit->nSizeWithAncestors;
+            packageFees = modit->nModFeesWithAncestors;
+            packageSigOps = modit->nSigOpCountWithAncestors;
+        }
+
+        if (packageFees < ::minRelayTxFee.GetFee(packageSize) && nBlockSize >= nBlockMinSize) {
+            // Everything else we might consider has a lower fee rate
+            return;
+        }
+
+        if (!TestPackage(packageSize, packageSigOps)) {
+            if (fUsingModified) {
+                // Since we always look at the best entry in mapModifiedTx,
+                // we must erase failed entries so that we can consider the
+                // next best entry on the next loop iteration
+                mapModifiedTx.get<ancestor_score>().erase(modit);
+                failedTx.insert(iter);
+            }
+            continue;
+        }
+
+        CTxMemPool::setEntries ancestors;
+        uint64_t nNoLimit = std::numeric_limits<uint64_t>::max();
+        std::string dummy;
+        mempool.CalculateMemPoolAncestors(*iter, ancestors, nNoLimit, nNoLimit, nNoLimit, nNoLimit, dummy, false);
+
+        onlyUnconfirmed(ancestors);
+        ancestors.insert(iter);
+
+        // Test if all tx's are Final
+        if (!TestPackageFinality(ancestors)) {
+            if (fUsingModified) {
+                mapModifiedTx.get<ancestor_score>().erase(modit);
+                failedTx.insert(iter);
+            }
+            continue;
+        }
+
+        // Package can be added. Sort the entries in a valid order.
+        vector<CTxMemPool::txiter> sortedEntries;
+        SortForBlock(ancestors, iter, sortedEntries);
+
+        for (size_t i=0; i<sortedEntries.size(); ++i) {
+            AddToBlock(sortedEntries[i]);
+            // Erase from the modified set, if present
+            mapModifiedTx.erase(sortedEntries[i]);
+        }
+
+        // Update transactions that depend on each of these
+        UpdatePackagesForAdded(ancestors, mapModifiedTx);
+    }
+}
+
 void BlockAssembler::addPriorityTxs()
 {
     // How much of the block should be dedicated to high-priority transactions,

src/miner.h

@@ -11,6 +11,8 @@
 
 #include <stdint.h>
 #include <memory>
+#include "boost/multi_index_container.hpp"
+#include "boost/multi_index/ordered_index.hpp"
 
 class CBlockIndex;
 class CChainParams;
@@ -29,6 +31,104 @@ struct CBlockTemplate
     std::vector<int64_t> vTxSigOps;
 };
 
+// Container for tracking updates to ancestor feerate as we include (parent)
+// transactions in a block
+struct CTxMemPoolModifiedEntry {
+    CTxMemPoolModifiedEntry(CTxMemPool::txiter entry)
+    {
+        iter = entry;
+        nSizeWithAncestors = entry->GetSizeWithAncestors();
+        nModFeesWithAncestors = entry->GetModFeesWithAncestors();
+        nSigOpCountWithAncestors = entry->GetSigOpCountWithAncestors();
+    }
+
+    CTxMemPool::txiter iter;
+    uint64_t nSizeWithAncestors;
+    CAmount nModFeesWithAncestors;
+    unsigned int nSigOpCountWithAncestors;
+};
+
+/** Comparator for CTxMemPool::txiter objects.
+ *  It simply compares the internal memory address of the CTxMemPoolEntry object
+ *  pointed to. This means it has no meaning, and is only useful for using them
+ *  as key in other indexes.
+ */
+struct CompareCTxMemPoolIter {
+    bool operator()(const CTxMemPool::txiter& a, const CTxMemPool::txiter& b) const
+    {
+        return &(*a) < &(*b);
+    }
+};
+
+struct modifiedentry_iter {
+    typedef CTxMemPool::txiter result_type;
+    result_type operator() (const CTxMemPoolModifiedEntry &entry) const
+    {
+        return entry.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)
+    {
+        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.
+struct CompareTxIterByAncestorCount {
+    bool operator()(const CTxMemPool::txiter &a, const CTxMemPool::txiter &b)
+    {
+        if (a->GetCountWithAncestors() != b->GetCountWithAncestors())
+            return a->GetCountWithAncestors() < b->GetCountWithAncestors();
+        return CTxMemPool::CompareIteratorByHash()(a, b);
+    }
+};
+
+typedef boost::multi_index_container<
+    CTxMemPoolModifiedEntry,
+    boost::multi_index::indexed_by<
+        boost::multi_index::ordered_unique<
+            modifiedentry_iter,
+            CompareCTxMemPoolIter
+        >,
+        // sorted by modified ancestor fee rate
+        boost::multi_index::ordered_non_unique<
+            // Reuse same tag from CTxMemPool's similar index
+            boost::multi_index::tag<ancestor_score>,
+            boost::multi_index::identity<CTxMemPoolModifiedEntry>,
+            CompareModifiedEntry
+        >
+    >
+> indexed_modified_transaction_set;
+
+typedef indexed_modified_transaction_set::nth_index<0>::type::iterator modtxiter;
+typedef indexed_modified_transaction_set::index<ancestor_score>::type::iterator modtxscoreiter;
+
+struct update_for_parent_inclusion
+{
+    update_for_parent_inclusion(CTxMemPool::txiter it) : iter(it) {}
+
+    void operator() (CTxMemPoolModifiedEntry &e)
+    {
+        e.nModFeesWithAncestors -= iter->GetFee();
+        e.nSizeWithAncestors -= iter->GetTxSize();
+        e.nSigOpCountWithAncestors -= iter->GetSigOpCount();
+    }
+
+    CTxMemPool::txiter iter;
+};
+
 /** Generate a new block, without valid proof-of-work */
 class BlockAssembler
 {
@@ -74,12 +174,30 @@ private:
     void addScoreTxs();
     /** Add transactions based on tx "priority" */
     void addPriorityTxs();
+    /** Add transactions based on feerate including unconfirmed ancestors */
+    void addPackageTxs();
 
     // helper function for addScoreTxs and addPriorityTxs
     /** Test if tx will still "fit" in the block */
     bool TestForBlock(CTxMemPool::txiter iter);
     /** Test if tx still has unconfirmed parents not yet in block */
     bool isStillDependent(CTxMemPool::txiter iter);
+
+    // helper functions for addPackageTxs()
+    /** Remove confirmed (inBlock) entries from given set */
+    void onlyUnconfirmed(CTxMemPool::setEntries& testSet);
+    /** Test if a new package would "fit" in the block */
+    bool TestPackage(uint64_t packageSize, unsigned int packageSigOps);
+    /** Test if a set of transactions are all final */
+    bool TestPackageFinality(const CTxMemPool::setEntries& package);
+    /** Return true if given transaction from mapTx has already been evaluated,
+      * or if the transaction's cached data in mapTx is incorrect. */
+    bool SkipMapTxEntry(CTxMemPool::txiter it, indexed_modified_transaction_set &mapModifiedTx, CTxMemPool::setEntries &failedTx);
+    /** Sort the package in an order that is valid to appear in a block */
+    void SortForBlock(const CTxMemPool::setEntries& package, CTxMemPool::txiter entry, std::vector<CTxMemPool::txiter>& sortedEntries);
+    /** Add descendants of given transactions to mapModifiedTx with ancestor
+      * state updated assuming given transactions are inBlock. */
+    void UpdatePackagesForAdded(const CTxMemPool::setEntries& alreadyAdded, indexed_modified_transaction_set &mapModifiedTx);
 };
 
 /** Modify the extranonce in a block */