Do not use the redundant BestInvalidWork record in the block database.

As block index entries have a flag for marking invalid blocks, the
'best invalid work' information can be derived from there. In addition,
remove the global from main.h

src/main.cpp

@@ -33,7 +33,7 @@ unsigned int nTransactionsUpdated = 0;
 
 map<uint256, CBlockIndex*> mapBlockIndex;
 CChain chainActive;
-uint256 nBestInvalidWork = 0;
+CBlockIndex *pindexBestInvalid;
 set<CBlockIndex*, CBlockIndexWorkComparator> setBlockIndexValid; // may contain all CBlockIndex*'s that have validness >=BLOCK_VALID_TRANSACTIONS, and must contain those who aren't failed
 int64 nTimeBestReceived = 0;
 int nScriptCheckThreads = 0;
@@ -1349,7 +1349,7 @@ void CheckForkWarningConditions()
     if (pindexBestForkTip && chainActive.Height() - pindexBestForkTip->nHeight >= 72)
         pindexBestForkTip = NULL;
 
-    if (pindexBestForkTip || nBestInvalidWork > chainActive.Tip()->nChainWork + (chainActive.Tip()->GetBlockWork() * 6).getuint256())
+    if (pindexBestForkTip || (pindexBestInvalid && pindexBestInvalid->nChainWork > chainActive.Tip()->nChainWork + (chainActive.Tip()->GetBlockWork() * 6).getuint256()))
     {
         if (!fLargeWorkForkFound)
         {
@@ -1416,10 +1416,13 @@ void CheckForkWarningConditionsOnNewFork(CBlockIndex* pindexNewForkTip)
 
 void static InvalidChainFound(CBlockIndex* pindexNew)
 {
-    if (pindexNew->nChainWork > nBestInvalidWork)
+    if (!pindexBestInvalid || pindexNew->nChainWork > pindexBestInvalid->nChainWork)
     {
-        nBestInvalidWork = pindexNew->nChainWork;
-        pblocktree->WriteBestInvalidWork(CBigNum(nBestInvalidWork));
+        pindexBestInvalid = pindexNew;
+        // The current code doesn't actually read the BestInvalidWork entry in
+        // the block database anymore, as it is derived from the flags in block
+        // index entry. We only write it for backward compatibility.
+        pblocktree->WriteBestInvalidWork(CBigNum(pindexBestInvalid->nChainWork));
         uiInterface.NotifyBlocksChanged();
     }
     LogPrintf("InvalidChainFound: invalid block=%s  height=%d  log2_work=%.8g  date=%s\n",
@@ -2769,6 +2772,8 @@ bool static LoadBlockIndexDB()
         pindex->nChainTx = (pindex->pprev ? pindex->pprev->nChainTx : 0) + pindex->nTx;
         if ((pindex->nStatus & BLOCK_VALID_MASK) >= BLOCK_VALID_TRANSACTIONS && !(pindex->nStatus & BLOCK_FAILED_MASK))
             setBlockIndexValid.insert(pindex);
+        if (pindex->nStatus & BLOCK_FAILED_MASK && (!pindexBestInvalid || pindex->nChainWork > pindexBestInvalid->nChainWork))
+            pindexBestInvalid = pindex;
     }
 
     // Load block file info
@@ -2777,11 +2782,6 @@ bool static LoadBlockIndexDB()
     if (pblocktree->ReadBlockFileInfo(nLastBlockFile, infoLastBlockFile))
         LogPrintf("LoadBlockIndexDB(): last block file info: %s\n", infoLastBlockFile.ToString().c_str());
 
-    // Load nBestInvalidWork, OK if it doesn't exist
-    CBigNum bnBestInvalidWork;
-    pblocktree->ReadBestInvalidWork(bnBestInvalidWork);
-    nBestInvalidWork = bnBestInvalidWork.getuint256();
-
     // Check whether we need to continue reindexing
     bool fReindexing = false;
     pblocktree->ReadReindexing(fReindexing);
@@ -2791,12 +2791,10 @@ bool static LoadBlockIndexDB()
     pblocktree->ReadFlag("txindex", fTxIndex);
     LogPrintf("LoadBlockIndexDB(): transaction index %s\n", fTxIndex ? "enabled" : "disabled");
 
-    // Load hashBestChain pointer to end of best chain
+    // Load pointer to end of best chain
     chainActive.SetTip(pcoinsTip->GetBestBlock());
     if (chainActive.Tip() == NULL)
         return true;
-
-    // register best chain
     LogPrintf("LoadBlockIndexDB(): hashBestChain=%s  height=%d date=%s\n",
         chainActive.Tip()->GetBlockHash().ToString().c_str(), chainActive.Height(),
         DateTimeStrFormat("%Y-%m-%d %H:%M:%S", chainActive.Tip()->GetBlockTime()).c_str());
@@ -2882,7 +2880,7 @@ void UnloadBlockIndex()
     mapBlockIndex.clear();
     setBlockIndexValid.clear();
     chainActive.SetTip(NULL);
-    nBestInvalidWork = 0;
+    pindexBestInvalid = NULL;
 }
 
 bool LoadBlockIndex()

src/main.h

@@ -74,7 +74,6 @@ extern CScript COINBASE_FLAGS;
 extern CCriticalSection cs_main;
 extern std::map<uint256, CBlockIndex*> mapBlockIndex;
 extern std::set<CBlockIndex*, CBlockIndexWorkComparator> setBlockIndexValid;
-extern uint256 nBestInvalidWork;
 extern unsigned int nTransactionsUpdated;
 extern uint64 nLastBlockTx;
 extern uint64 nLastBlockSize;

src/txdb.cpp

@@ -74,13 +74,9 @@ bool CBlockTreeDB::WriteBlockIndex(const CDiskBlockIndex& blockindex)
     return Write(make_pair('b', blockindex.GetBlockHash()), blockindex);
 }
 
-bool CBlockTreeDB::ReadBestInvalidWork(CBigNum& bnBestInvalidWork)
-{
-    return Read('I', bnBestInvalidWork);
-}
-
 bool CBlockTreeDB::WriteBestInvalidWork(const CBigNum& bnBestInvalidWork)
 {
+    // Obsolete; only written for backward compatibility.
     return Write('I', bnBestInvalidWork);
 }
 

src/txdb.h

@@ -35,7 +35,6 @@ private:
     void operator=(const CBlockTreeDB&);
 public:
     bool WriteBlockIndex(const CDiskBlockIndex& blockindex);
-    bool ReadBestInvalidWork(CBigNum& bnBestInvalidWork);
     bool WriteBestInvalidWork(const CBigNum& bnBestInvalidWork);
     bool ReadBlockFileInfo(int nFile, CBlockFileInfo &fileinfo);
     bool WriteBlockFileInfo(int nFile, const CBlockFileInfo &fileinfo);