Adds an expiration time for orphan tx.

gmaxwell · furszy · commit 59ff5900def2 · 2021-04-15T13:07:21.000-03:00
This prevents higher order orphans and other junk from
holding positions in the orphan map.  Parents delayed
twenty minutes are more are unlikely to ever arrive.

The freed space will improve the orphan matching success rate for
other transactions.
diff --git a/src/net_processing.cpp b/src/net_processing.cpp
@@ -34,6 +34,7 @@ struct IteratorComparator
 struct COrphanTx {
     CTransactionRef tx;
     NodeId fromPeer;
+    int64_t nTimeExpire;
 };
 
 std::map<uint256, COrphanTx> mapOrphanTransactions GUARDED_BY(cs_main);
@@ -518,7 +519,7 @@ bool AddOrphanTx(const CTransactionRef& tx, NodeId peer) EXCLUSIVE_LOCKS_REQUIRE
         return false;
     }
 
-    auto ret = mapOrphanTransactions.emplace(hash, COrphanTx{tx, peer});
+    auto ret = mapOrphanTransactions.emplace(hash, COrphanTx{tx, peer, GetTime() + ORPHAN_TX_EXPIRE_TIME});
     assert(ret.second);
     for (const CTxIn& txin : tx->vin) {
         mapOrphanTransactionsByPrev[txin.prevout].insert(ret.first);
@@ -563,6 +564,25 @@ void EraseOrphansFor(NodeId peer) EXCLUSIVE_LOCKS_REQUIRED(cs_main)
 unsigned int LimitOrphanTxSize(unsigned int nMaxOrphans) EXCLUSIVE_LOCKS_REQUIRED(cs_main)
 {
     unsigned int nEvicted = 0;
+    static int64_t nNextSweep;
+    int64_t nNow = GetTime();
+    if (nNextSweep <= nNow) {
+        // Sweep out expired orphan pool entries:
+        int nErased = 0;
+        int64_t nMinExpTime = nNow + ORPHAN_TX_EXPIRE_TIME - ORPHAN_TX_EXPIRE_INTERVAL;
+        auto iter = mapOrphanTransactions.begin();
+        while (iter != mapOrphanTransactions.end()) {
+            auto maybeErase = iter++;
+            if (maybeErase->second.nTimeExpire <= nNow) {
+                nErased += EraseOrphanTx(maybeErase->second.tx->GetHash());
+            } else {
+                nMinExpTime = std::min(maybeErase->second.nTimeExpire, nMinExpTime);
+            }
+        }
+        // Sweep again 5 minutes after the next entry that expires in order to batch the linear scan.
+        nNextSweep = nMinExpTime + ORPHAN_TX_EXPIRE_INTERVAL;
+        if (nErased > 0) LogPrint(BCLog::MEMPOOL, "Erased %d orphan tx due to expiration\n", nErased);
+    }
     FastRandomContext rng;
     while (mapOrphanTransactions.size() > nMaxOrphans) {
         // Evict a random orphan:
diff --git a/src/net_processing.h b/src/net_processing.h
@@ -14,6 +14,10 @@ extern RecursiveMutex cs_main; // !TODO: change mutex to cs_orphans
 
 /** Default for -maxorphantx, maximum number of orphan transactions kept in memory */
 static const unsigned int DEFAULT_MAX_ORPHAN_TRANSACTIONS = 100;
+/** Expiration time for orphan transactions in seconds */
+static const int64_t ORPHAN_TX_EXPIRE_TIME = 20 * 60;
+/** Minimum time between orphan transactions expire time checks in seconds */
+static const int64_t ORPHAN_TX_EXPIRE_INTERVAL = 5 * 60;
 /** Default for -blockspamfilter, use header spam filter */
 static const bool DEFAULT_BLOCK_SPAM_FILTER = true;
 /** Default for -blockspamfiltermaxsize, maximum size of the list of indexes in the block spam filter */
