From 4fea06db25108e7f72710bf22c3d1896707eeb74 Mon Sep 17 00:00:00 2001
From: Pieter Wuille <pieter.wuille@gmail.com>
Date: Fri, 10 Aug 2012 15:13:57 +0200
Subject: [PATCH] Automatically reorganize at startup to best known block

Given that the block tree database (chain.dat) and the active chain
database (coins.dat) are entirely separate now, it becomes legal to
swap one with another instance without affecting the other.

This commit introduces a check in the startup code that detects the
presence of a better chain in chain.dat that has not been activated
yet, and does so efficiently (in batch, while reusing the blk???.dat
files).
---
 src/db.cpp   |  1 -
 src/init.cpp | 34 ++++++++++++++++++++++++++++++++++
 2 files changed, 34 insertions(+), 1 deletion(-)

diff --git a/src/db.cpp b/src/db.cpp
index 06e5543b..5ca9ea2c 100644
--- a/src/db.cpp
+++ b/src/db.cpp
@@ -636,7 +636,6 @@ bool LoadBlockIndex(CChainDB &chaindb)
     {
         if (pindexGenesisBlock == NULL)
             return true;
-        return error("CTxDB::LoadBlockIndex() : hashBestChain not loaded");
     }
     hashBestChain = pindexBest->GetBlockHash();
     nBestHeight = pindexBest->nHeight;
diff --git a/src/init.cpp b/src/init.cpp
index b05d57ab..85aa4f60 100644
--- a/src/init.cpp
+++ b/src/init.cpp
@@ -780,6 +780,40 @@ bool AppInit2()
 
     // ********************************************************* Step 9: import blocks
 
+    // scan for better chains in the block chain database, that are not yet connected in the active best chain
+    CBlockIndex *pindexFoundBest = pindexBest;
+    for (std::map<uint256,CBlockIndex*>::iterator it = mapBlockIndex.begin(); it != mapBlockIndex.end(); it++) {
+        CBlockIndex *pindex = it->second;
+        if (pindexFoundBest==NULL || pindex->bnChainWork > pindexFoundBest->bnChainWork)
+            pindexFoundBest = pindex;
+    }
+    if (pindexFoundBest != pindexBest) {
+        uiInterface.InitMessage(_("Importing blocks from block database..."));
+        uint64 nTxs = 0;
+        uint64 nBlocks = 0;
+        std::vector<CBlockIndex*> vAttach;
+        vAttach.reserve(pindexFoundBest->nHeight - (pindexBest==NULL ? 0 : pindexBest->nHeight));
+        while (pindexFoundBest && pindexFoundBest->bnChainWork > (pindexBest==NULL ? 0 : pindexBest->bnChainWork)) {
+            vAttach.push_back(pindexFoundBest);
+            pindexFoundBest = pindexFoundBest->pprev;
+        }
+        for (std::vector<CBlockIndex*>::reverse_iterator it = vAttach.rbegin(); it != vAttach.rend(); it++) {
+            CBlockIndex *pindex = *it;
+            CBlock block;
+            if (!block.ReadFromDisk(pindex))
+                break;
+            nTxs += block.vtx.size();
+            nBlocks++;
+            if (pindex->nHeight == 0 || nTxs + nBlocks*3 > 500) {
+                nTxs=0;
+                nBlocks=0;
+                block.SetBestChain(pindex);
+            }
+            if (fRequestShutdown)
+                break;
+        }
+    }
+
     std::vector<boost::filesystem::path> *vPath = new std::vector<boost::filesystem::path>();
     if (mapArgs.count("-loadblock"))
     {