From c72b2908788f69eb7403b113922f6e0ee74db267 Mon Sep 17 00:00:00 2001
From: Pieter Wuille <pieter.wuille@gmail.com>
Date: Wed, 20 Apr 2016 16:02:19 +0200
Subject: [PATCH] Optimize ActivateBestChain for long chains

---
 src/main.cpp | 18 ++++++++++++------
 1 file changed, 12 insertions(+), 6 deletions(-)

diff --git a/src/main.cpp b/src/main.cpp
index ec08c2110..eb0423236 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -3340,10 +3340,9 @@ static void PruneBlockIndexCandidates() {
  * Try to make some progress towards making pindexMostWork the active block.
  * pblock is either NULL or a pointer to a CBlock corresponding to pindexMostWork.
  */
-static bool ActivateBestChainStep(CValidationState& state, const CChainParams& chainparams, CBlockIndex* pindexMostWork, const CBlock* pblock)
+static bool ActivateBestChainStep(CValidationState& state, const CChainParams& chainparams, CBlockIndex* pindexMostWork, const CBlock* pblock, bool& fInvalidFound)
 {
     AssertLockHeld(cs_main);
-    bool fInvalidFound = false;
     const CBlockIndex *pindexOldTip = chainActive.Tip();
     const CBlockIndex *pindexFork = chainActive.FindFork(pindexMostWork);
 
@@ -3431,16 +3430,23 @@ bool ActivateBestChain(CValidationState &state, const CChainParams& chainparams,
         {
             LOCK(cs_main);
             CBlockIndex *pindexOldTip = chainActive.Tip();
-            pindexMostWork = FindMostWorkChain();
+            if (pindexMostWork == NULL) {
+                pindexMostWork = FindMostWorkChain();
+            }
 
             // Whether we have anything to do at all.
             if (pindexMostWork == NULL || pindexMostWork == chainActive.Tip())
                 return true;
 
-            if (!ActivateBestChainStep(state, chainparams, pindexMostWork, pblock && (*phash) == pindexMostWork->GetBlockHash() ? pblock : NULL))
-            	return false;
+            bool fInvalidFound = false;
+            if (!ActivateBestChainStep(state, chainparams, pindexMostWork, pblock && (*phash) == pindexMostWork->GetBlockHash() ? pblock : NULL, fInvalidFound))
+                return false;
 
-			pindexNewTip = chainActive.Tip();
+            if (fInvalidFound) {
+                // Wipe cache, we may need another branch now.
+                pindexMostWork = NULL;
+            }
+            pindexNewTip = chainActive.Tip();
             pindexFork = chainActive.FindFork(pindexOldTip);
             fInitialDownload = IsInitialBlockDownload();
         }