From fb8fad1586ced69fa37c665a11916ae4c4d0df05 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 | 14 ++++++++++----
 1 file changed, 10 insertions(+), 4 deletions(-)

diff --git a/src/main.cpp b/src/main.cpp
index 42733ee2d..38851cda3 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -2811,10 +2811,9 @@ 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);
 
@@ -2902,15 +2901,22 @@ 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 && pblock->GetHash() == pindexMostWork->GetBlockHash() ? pblock : NULL))
+            bool fInvalidFound = false;
+            if (!ActivateBestChainStep(state, chainparams, pindexMostWork, pblock && pblock->GetHash() == pindexMostWork->GetBlockHash() ? pblock : NULL, fInvalidFound))
                 return false;
 
+            if (fInvalidFound) {
+                // Wipe cache, we may need another branch now.
+                pindexMostWork = NULL;
+            }
             pindexNewTip = chainActive.Tip();
             pindexFork = chainActive.FindFork(pindexOldTip);
             fInitialDownload = IsInitialBlockDownload();