Provide a flat list of txid/terators to txn in CTxMemPool

src/txmempool.cpp

@@ -438,6 +438,9 @@ bool CTxMemPool::addUnchecked(const uint256& hash, const CTxMemPoolEntry &entry,
     totalTxSize += entry.GetTxSize();
     minerPolicyEstimator->processTransaction(entry, fCurrentEstimate);
 
+    vTxHashes.emplace_back(hash, newit);
+    newit->vTxHashesIdx = vTxHashes.size() - 1;
+
     return true;
 }
 
@@ -447,6 +450,15 @@ void CTxMemPool::removeUnchecked(txiter it)
     BOOST_FOREACH(const CTxIn& txin, it->GetTx().vin)
         mapNextTx.erase(txin.prevout);
 
+    if (vTxHashes.size() > 1) {
+        vTxHashes[it->vTxHashesIdx] = std::move(vTxHashes.back());
+        vTxHashes[it->vTxHashesIdx].second->vTxHashesIdx = it->vTxHashesIdx;
+        vTxHashes.pop_back();
+        if (vTxHashes.size() * 2 < vTxHashes.capacity())
+            vTxHashes.shrink_to_fit();
+    } else
+        vTxHashes.clear();
+
     totalTxSize -= it->GetTxSize();
     cachedInnerUsage -= it->DynamicMemoryUsage();
     cachedInnerUsage -= memusage::DynamicUsage(mapLinks[it].parents) + memusage::DynamicUsage(mapLinks[it].children);
@@ -965,7 +977,7 @@ bool CCoinsViewMemPool::HaveCoins(const uint256 &txid) const {
 size_t CTxMemPool::DynamicMemoryUsage() const {
     LOCK(cs);
     // Estimate the overhead of mapTx to be 15 pointers + an allocation, as no exact formula for boost::multi_index_contained is implemented.
-    return memusage::MallocUsage(sizeof(CTxMemPoolEntry) + 15 * sizeof(void*)) * mapTx.size() + memusage::DynamicUsage(mapNextTx) + memusage::DynamicUsage(mapDeltas) + memusage::DynamicUsage(mapLinks) + cachedInnerUsage;
+    return memusage::MallocUsage(sizeof(CTxMemPoolEntry) + 15 * sizeof(void*)) * mapTx.size() + memusage::DynamicUsage(mapNextTx) + memusage::DynamicUsage(mapDeltas) + memusage::DynamicUsage(mapLinks) + memusage::DynamicUsage(vTxHashes) + cachedInnerUsage;
 }
 
 void CTxMemPool::RemoveStaged(setEntries &stage, bool updateDescendants) {

src/txmempool.h

@@ -150,6 +150,8 @@ public:
     uint64_t GetSizeWithAncestors() const { return nSizeWithAncestors; }
     CAmount GetModFeesWithAncestors() const { return nModFeesWithAncestors; }
     unsigned int GetSigOpCountWithAncestors() const { return nSigOpCountWithAncestors; }
+
+    mutable size_t vTxHashesIdx; //!< Index in mempool's vTxHashes
 };
 
 // Helpers for modifying CTxMemPool::mapTx, which is a boost multi_index.
@@ -457,7 +459,10 @@ public:
 
     mutable CCriticalSection cs;
     indexed_transaction_set mapTx;
+
     typedef indexed_transaction_set::nth_index<0>::type::iterator txiter;
+    std::vector<std::pair<uint256, txiter> > vTxHashes; //!< All tx hashes/entries in mapTx, in random order
+
     struct CompareIteratorByHash {
         bool operator()(const txiter &a, const txiter &b) const {
             return a->GetTx().GetHash() < b->GetTx().GetHash();