Mining: return early when block is almost full

src/miner.cpp

@@ -358,6 +358,13 @@ void BlockAssembler::addPackageTxs()
 
     CTxMemPool::indexed_transaction_set::index<ancestor_score>::type::iterator mi = mempool.mapTx.get<ancestor_score>().begin();
     CTxMemPool::txiter iter;
+
+    // Limit the number of attempts to add transactions to the block when it is
+    // close to full; this is just a simple heuristic to finish quickly if the
+    // mempool has a lot of entries.
+    const int64_t MAX_CONSECUTIVE_FAILURES = 1000;
+    int64_t nConsecutiveFailed = 0;
+
     while (mi != mempool.mapTx.get<ancestor_score>().end() || !mapModifiedTx.empty())
     {
         // First try to find a new transaction in mapTx to evaluate.
@@ -419,6 +426,14 @@ void BlockAssembler::addPackageTxs()
                 mapModifiedTx.get<ancestor_score>().erase(modit);
                 failedTx.insert(iter);
             }
+
+            ++nConsecutiveFailed;
+
+            if (nConsecutiveFailed > MAX_CONSECUTIVE_FAILURES && nBlockWeight >
+                    nBlockMaxWeight - 4000) {
+                // Give up if we're close to full and haven't succeeded in a while
+                break;
+            }
             continue;
         }
 
@@ -439,6 +454,9 @@ void BlockAssembler::addPackageTxs()
             continue;
         }
 
+        // This transaction will make it in; reset the failed counter.
+        nConsecutiveFailed = 0;
+
         // Package can be added. Sort the entries in a valid order.
         std::vector<CTxMemPool::txiter> sortedEntries;
         SortForBlock(ancestors, iter, sortedEntries);