One file per block

Refactor of the block storage code, which now stores one file per block.
This will allow easier pruning, as blocks can be removed individually.

src/db.cpp

@@ -637,12 +637,12 @@ bool CTxDB::LoadBlockIndex()
         nCheckDepth = nBestHeight;
     printf("Verifying last %i blocks at level %i\n", nCheckDepth, nCheckLevel);
     CBlockIndex* pindexFork = NULL;
-    map<pair<unsigned int, unsigned int>, CBlockIndex*> mapBlockPos;
     for (CBlockIndex* pindex = pindexBest; pindex && pindex->pprev; pindex = pindex->pprev)
     {
         if (fRequestShutdown || pindex->nHeight < nBestHeight-nCheckDepth)
             break;
         CBlock block;
+        CDiskBlockPos blockPos = pindex->GetBlockPos();
         if (!block.ReadFromDisk(pindex))
             return error("LoadBlockIndex() : block.ReadFromDisk failed");
         // check level 1: verify block validity
@@ -654,8 +654,6 @@ bool CTxDB::LoadBlockIndex()
         // check level 2: verify transaction index validity
         if (nCheckLevel>1)
         {
-            pair<unsigned int, unsigned int> pos = make_pair(pindex->nFile, pindex->nBlockPos);
-            mapBlockPos[pos] = pindex;
             BOOST_FOREACH(const CTransaction &tx, block.vtx)
             {
                 uint256 hashTx = tx.GetHash();
@@ -663,7 +661,7 @@ bool CTxDB::LoadBlockIndex()
                 if (ReadTxIndex(hashTx, txindex))
                 {
                     // check level 3: checker transaction hashes
-                    if (nCheckLevel>2 || pindex->nFile != txindex.pos.nFile || pindex->nBlockPos != txindex.pos.nBlockPos)
+                    if (nCheckLevel>2 || blockPos != txindex.pos.blockPos)
                     {
                         // either an error or a duplicate transaction
                         CTransaction txFound;
@@ -687,12 +685,6 @@ bool CTxDB::LoadBlockIndex()
                         {
                             if (!txpos.IsNull())
                             {
-                                pair<unsigned int, unsigned int> posFind = make_pair(txpos.nFile, txpos.nBlockPos);
-                                if (!mapBlockPos.count(posFind))
-                                {
-                                    printf("LoadBlockIndex(): *** found bad spend at %d, hashBlock=%s, hashTx=%s\n", pindex->nHeight, pindex->GetBlockHash().ToString().c_str(), hashTx.ToString().c_str());
-                                    pindexFork = pindex->pprev;
-                                }
                                 // check level 6: check whether spent txouts were spent by a valid transaction that consume them
                                 if (nCheckLevel>5)
                                 {
@@ -795,9 +787,8 @@ bool CTxDB::LoadBlockIndexGuts()
             CBlockIndex* pindexNew = InsertBlockIndex(diskindex.GetBlockHash());
             pindexNew->pprev          = InsertBlockIndex(diskindex.hashPrev);
             pindexNew->pnext          = InsertBlockIndex(diskindex.hashNext);
-            pindexNew->nFile          = diskindex.nFile;
-            pindexNew->nBlockPos      = diskindex.nBlockPos;
             pindexNew->nHeight        = diskindex.nHeight;
+            pindexNew->nAlternative   = diskindex.nAlternative;
             pindexNew->nVersion       = diskindex.nVersion;
             pindexNew->hashMerkleRoot = diskindex.hashMerkleRoot;
             pindexNew->nTime          = diskindex.nTime;

src/main.cpp

@@ -389,7 +389,7 @@ int CMerkleTx::SetMerkleBranch(const CBlock* pblock)
             CTxIndex txindex;
             if (!CTxDB("r").ReadTxIndex(GetHash(), txindex))
                 return 0;
-            if (!blockTmp.ReadFromDisk(txindex.pos.nFile, txindex.pos.nBlockPos))
+            if (!blockTmp.ReadFromDisk(txindex.pos.blockPos))
                 return 0;
             pblock = &blockTmp;
         }
@@ -646,7 +646,7 @@ bool CTxMemPool::accept(CTxDB& txdb, CTransaction &tx, bool fCheckInputs,
 
         // Check against previous transactions
         // This is done last to help prevent CPU exhaustion denial-of-service attacks.
-        if (!tx.ConnectInputs(mapInputs, mapUnused, CDiskTxPos(1,1,1), pindexBest, false, false))
+        if (!tx.ConnectInputs(mapInputs, mapUnused, CDiskTxPos(true), pindexBest, false, false))
         {
             return error("CTxMemPool::accept() : ConnectInputs failed %s", hash.ToString().substr(0,10).c_str());
         }
@@ -817,7 +817,7 @@ int CTxIndex::GetDepthInMainChain() const
 {
     // Read block header
     CBlock block;
-    if (!block.ReadFromDisk(pos.nFile, pos.nBlockPos, false))
+    if (!block.ReadFromDisk(pos.blockPos, false))
         return 0;
     // Find the block in the index
     map<uint256, CBlockIndex*>::iterator mi = mapBlockIndex.find(block.GetHash());
@@ -847,7 +847,7 @@ bool GetTransaction(const uint256 &hash, CTransaction &tx, uint256 &hashBlock)
         if (tx.ReadFromDisk(txdb, COutPoint(hash, 0), txindex))
         {
             CBlock block;
-            if (block.ReadFromDisk(txindex.pos.nFile, txindex.pos.nBlockPos, false))
+            if (block.ReadFromDisk(txindex.pos.blockPos, false))
                 hashBlock = block.GetHash();
             return true;
         }
@@ -892,7 +892,7 @@ bool CBlock::ReadFromDisk(const CBlockIndex* pindex, bool fReadTransactions)
         *this = pindex->GetBlockHeader();
         return true;
     }
-    if (!ReadFromDisk(pindex->nFile, pindex->nBlockPos, fReadTransactions))
+    if (!ReadFromDisk(pindex->GetBlockPos(), fReadTransactions))
         return false;
     if (GetHash() != pindex->GetBlockHash())
         return error("CBlock::ReadFromDisk() : GetHash() doesn't match index");
@@ -1156,7 +1156,7 @@ bool CTransaction::FetchInputs(CTxDB& txdb, const map<uint256, CTxIndex>& mapTes
 
         // Read txPrev
         CTransaction& txPrev = inputsRet[prevout.hash].second;
-        if (!fFound || txindex.pos == CDiskTxPos(1,1,1))
+        if (!fFound || txindex.pos.IsMemPool())
         {
             // Get prev tx from single transactions in memory
             {
@@ -1262,7 +1262,7 @@ bool CTransaction::ConnectInputs(MapPrevTx inputs,
             // If prev is coinbase, check that it's matured
             if (txPrev.IsCoinBase())
                 for (const CBlockIndex* pindex = pindexBlock; pindex && pindexBlock->nHeight - pindex->nHeight < COINBASE_MATURITY; pindex = pindex->pprev)
-                    if (pindex->nBlockPos == txindex.pos.nBlockPos && pindex->nFile == txindex.pos.nFile)
+                    if (pindex->GetBlockPos() == txindex.pos.blockPos)
                         return error("ConnectInputs() : tried to spend coinbase at depth %d", pindexBlock->nHeight - pindex->nHeight);
 
             // Check for negative or overflow input values
@@ -1427,11 +1427,10 @@ bool CBlock::ConnectBlock(CTxDB& txdb, CBlockIndex* pindex, bool fJustCheck)
     //// issue here: it doesn't know the version
     unsigned int nTxPos;
     if (fJustCheck)
-        // FetchInputs treats CDiskTxPos(1,1,1) as a special "refer to memorypool" indicator
         // Since we're just checking the block and not actually connecting it, it might not (and probably shouldn't) be on the disk to get the transaction from
         nTxPos = 1;
     else
-        nTxPos = pindex->nBlockPos + ::GetSerializeSize(CBlock(), SER_DISK, CLIENT_VERSION) - 1 + GetSizeOfCompactSize(vtx.size());
+        nTxPos = ::GetSerializeSize(CBlock(), SER_DISK, CLIENT_VERSION) - 1 + GetSizeOfCompactSize(vtx.size());
 
     map<uint256, CTxIndex> mapQueuedChanges;
     int64 nFees = 0;
@@ -1453,9 +1452,11 @@ bool CBlock::ConnectBlock(CTxDB& txdb, CBlockIndex* pindex, bool fJustCheck)
         if (nSigOps > MAX_BLOCK_SIGOPS)
             return DoS(100, error("ConnectBlock() : too many sigops"));
 
-        CDiskTxPos posThisTx(pindex->nFile, pindex->nBlockPos, nTxPos);
+        CDiskTxPos posThisTx(pindex->GetBlockPos(), nTxPos);
         if (!fJustCheck)
             nTxPos += ::GetSerializeSize(tx, SER_DISK, CLIENT_VERSION);
+        else
+            posThisTx = CDiskTxPos(true);
 
         MapPrevTx mapInputs;
         if (!tx.IsCoinBase())
@@ -1750,7 +1751,7 @@ bool CBlock::SetBestChain(CTxDB& txdb, CBlockIndex* pindexNew)
 }
 
 
-bool CBlock::AddToBlockIndex(unsigned int nFile, unsigned int nBlockPos)
+bool CBlock::AddToBlockIndex(const CDiskBlockPos &pos)
 {
     // Check for duplicate
     uint256 hash = GetHash();
@@ -1758,7 +1759,7 @@ bool CBlock::AddToBlockIndex(unsigned int nFile, unsigned int nBlockPos)
         return error("AddToBlockIndex() : %s already exists", hash.ToString().substr(0,20).c_str());
 
     // Construct new block index object
-    CBlockIndex* pindexNew = new CBlockIndex(nFile, nBlockPos, *this);
+    CBlockIndex* pindexNew = new CBlockIndex(*this);
     if (!pindexNew)
         return error("AddToBlockIndex() : new CBlockIndex failed");
     map<uint256, CBlockIndex*>::iterator mi = mapBlockIndex.insert(make_pair(hash, pindexNew)).first;
@@ -1770,6 +1771,8 @@ bool CBlock::AddToBlockIndex(unsigned int nFile, unsigned int nBlockPos)
         pindexNew->nHeight = pindexNew->pprev->nHeight + 1;
     }
     pindexNew->bnChainWork = (pindexNew->pprev ? pindexNew->pprev->bnChainWork : 0) + pindexNew->GetBlockWork();
+    assert(pos.nHeight == pindexNew->nHeight);
+    pindexNew->nAlternative = pos.nAlternative;
 
     CTxDB txdb;
     if (!txdb.TxnBegin())
@@ -1908,13 +1911,12 @@ bool CBlock::AcceptBlock()
     }
 
     // Write block to history file
+    CDiskBlockPos blockPos = CDiskBlockPos(nHeight);
     if (!CheckDiskSpace(::GetSerializeSize(*this, SER_DISK, CLIENT_VERSION)))
         return error("AcceptBlock() : out of disk space");
-    unsigned int nFile = -1;
-    unsigned int nBlockPos = 0;
-    if (!WriteToDisk(nFile, nBlockPos))
+    if (!WriteToDisk(blockPos))
         return error("AcceptBlock() : WriteToDisk failed");
-    if (!AddToBlockIndex(nFile, nBlockPos))
+    if (!AddToBlockIndex(blockPos))
         return error("AcceptBlock() : AddToBlockIndex failed");
 
     // Relay inventory, but don't relay old inventory during initial block download
@@ -2048,53 +2050,18 @@ bool CheckDiskSpace(uint64 nAdditionalBytes)
     return true;
 }
 
-static filesystem::path BlockFilePath(unsigned int nFile)
+FILE* OpenBlockFile(const CDiskBlockPos &pos, const char* pszMode)
 {
-    string strBlockFn = strprintf("blk%04u.dat", nFile);
-    return GetDataDir() / strBlockFn;
-}
-
-FILE* OpenBlockFile(unsigned int nFile, unsigned int nBlockPos, const char* pszMode)
-{
-    if ((nFile < 1) || (nFile == (unsigned int) -1))
+    boost::filesystem::path path = pos.GetFileName(GetDataDir());
+    boost::filesystem::create_directories(path.parent_path());
+    if (pos.IsNull() || pos.IsMemPool())
         return NULL;
-    FILE* file = fopen(BlockFilePath(nFile).string().c_str(), pszMode);
+    FILE* file = fopen(path.string().c_str(), pszMode);
     if (!file)
         return NULL;
-    if (nBlockPos != 0 && !strchr(pszMode, 'a') && !strchr(pszMode, 'w'))
-    {
-        if (fseek(file, nBlockPos, SEEK_SET) != 0)
-        {
-            fclose(file);
-            return NULL;
-        }
-    }
     return file;
 }
 
-static unsigned int nCurrentBlockFile = 1;
-
-FILE* AppendBlockFile(unsigned int& nFileRet)
-{
-    nFileRet = 0;
-    loop
-    {
-        FILE* file = OpenBlockFile(nCurrentBlockFile, 0, "ab");
-        if (!file)
-            return NULL;
-        if (fseek(file, 0, SEEK_END) != 0)
-            return NULL;
-        // FAT32 file size max 4GB, fseek and ftell max 2GB, so we must stay under 2GB
-        if (ftell(file) < (long)(0x7F000000 - MAX_SIZE))
-        {
-            nFileRet = nCurrentBlockFile;
-            return file;
-        }
-        fclose(file);
-        nCurrentBlockFile++;
-    }
-}
-
 bool LoadBlockIndex(bool fAllowNew)
 {
     if (fTestNet)
@@ -2153,19 +2120,19 @@ bool LoadBlockIndex(bool fAllowNew)
         }
 
         //// debug print
-        printf("%s\n", block.GetHash().ToString().c_str());
+        uint256 hash = block.GetHash();
+        printf("%s\n", hash.ToString().c_str());
         printf("%s\n", hashGenesisBlock.ToString().c_str());
         printf("%s\n", block.hashMerkleRoot.ToString().c_str());
         assert(block.hashMerkleRoot == uint256("0x4a5e1e4baab89f3a32518a88c31bc87f618f76673e2cc77ab2127b7afdeda33b"));
         block.print();
-        assert(block.GetHash() == hashGenesisBlock);
+        assert(hash == hashGenesisBlock);
 
         // Start new block file
-        unsigned int nFile;
-        unsigned int nBlockPos;
-        if (!block.WriteToDisk(nFile, nBlockPos))
+        CDiskBlockPos blockPos(0);
+        if (!block.WriteToDisk(blockPos))
             return error("LoadBlockIndex() : writing genesis block to disk failed");
-        if (!block.AddToBlockIndex(nFile, nBlockPos))
+        if (!block.AddToBlockIndex(blockPos))
             return error("LoadBlockIndex() : genesis block not accepted");
     }
 
@@ -2219,11 +2186,9 @@ void PrintBlockTree()
         // print item
         CBlock block;
         block.ReadFromDisk(pindex);
-        printf("%d (%u,%u) %s  %s  tx %"PRIszu"",
+        printf("%d (%s)  %s  tx %"PRIszu"",
             pindex->nHeight,
-            pindex->nFile,
-            pindex->nBlockPos,
-            block.GetHash().ToString().substr(0,20).c_str(),
+            pindex->GetBlockPos().GetFileName("").string().c_str(),
             DateTimeStrFormat("%x %H:%M:%S", block.GetBlockTime()).c_str(),
             block.vtx.size());
 
@@ -3693,9 +3658,9 @@ CBlock* CreateNewBlock(CReserveKey& reservekey)
             if (nBlockSigOps + nTxSigOps >= MAX_BLOCK_SIGOPS)
                 continue;
 
-            if (!tx.ConnectInputs(mapInputs, mapTestPoolTmp, CDiskTxPos(1,1,1), pindexPrev, false, true))
+            if (!tx.ConnectInputs(mapInputs, mapTestPoolTmp, CDiskTxPos(true), pindexPrev, false, true))
                 continue;
-            mapTestPoolTmp[tx.GetHash()] = CTxIndex(CDiskTxPos(1,1,1), tx.vout.size());
+            mapTestPoolTmp[tx.GetHash()] = CTxIndex(CDiskTxPos(true), tx.vout.size());
             swap(mapTestPool, mapTestPoolTmp);
 
             // Added
@@ -3743,7 +3708,7 @@ CBlock* CreateNewBlock(CReserveKey& reservekey)
     pblock->nNonce         = 0;
 
         pblock->vtx[0].vin[0].scriptSig = scriptDummy;
-        CBlockIndex indexDummy(1, 1, *pblock);
+        CBlockIndex indexDummy(*pblock);
         indexDummy.pprev = pindexPrev;
         indexDummy.nHeight = pindexPrev->nHeight + 1;
         if (!pblock->ConnectBlock(txdb, &indexDummy, true))

src/main.h

@@ -80,14 +80,14 @@ static const uint64 nMinDiskSpace = 52428800;
 class CReserveKey;
 class CTxDB;
 class CTxIndex;
+class CDiskBlockPos;
 
 void RegisterWallet(CWallet* pwalletIn);
 void UnregisterWallet(CWallet* pwalletIn);
 void SyncWithWallets(const CTransaction& tx, const CBlock* pblock = NULL, bool fUpdate = false);
 bool ProcessBlock(CNode* pfrom, CBlock* pblock);
 bool CheckDiskSpace(uint64 nAdditionalBytes=0);
-FILE* OpenBlockFile(unsigned int nFile, unsigned int nBlockPos, const char* pszMode="rb");
-FILE* AppendBlockFile(unsigned int& nFileRet);
+FILE* OpenBlockFile(const CDiskBlockPos &pos, const char* pszMode="rb");
 bool LoadBlockIndex(bool fAllowNew=true);
 void PrintBlockTree();
 CBlockIndex* FindBlockByHeight(int nHeight);
@@ -118,34 +118,115 @@ bool GetTransaction(const uint256 &hash, CTransaction &tx, uint256 &hashBlock);
 
 bool GetWalletFile(CWallet* pwallet, std::string &strWalletFileOut);
 
+class CDiskBlockPos
+{
+public:
+    int nHeight;
+    int nAlternative;
+
+    CDiskBlockPos() {
+        SetNull();
+    }
+
+    CDiskBlockPos(int nHeightIn, int nAlternativeIn = 0) {
+        nHeight = nHeightIn;
+        nAlternative = nAlternativeIn;
+    }
+
+    std::string GetAlternative() const {
+        char c[9]={0,0,0,0,0,0,0,0,0};
+        char *cp = &c[8];
+        unsigned int n = nAlternative;
+        while (n > 0 && cp>c) {
+            n--;
+            *(--cp) = 'a' + (n % 26);
+            n /= 26;
+        }
+        return std::string(cp);
+    }
+
+    boost::filesystem::path GetDirectory(const boost::filesystem::path &base) const {
+        assert(nHeight != -1);
+        return base / strprintf("era%02u", nHeight / 210000) / 
+                      strprintf("cycle%04u", nHeight / 2016);
+    }
+
+    boost::filesystem::path GetFileName(const boost::filesystem::path &base) const {
+        return GetDirectory(base) / strprintf("%08u%s.blk", nHeight, GetAlternative().c_str());
+    }
+
+    // TODO: make thread-safe (lockfile, atomic file creation, ...?)
+    void MakeUnique(const boost::filesystem::path &base) {
+        while (boost::filesystem::exists(GetFileName(base)))
+            nAlternative++;
+    }
+
+    IMPLEMENT_SERIALIZE(({
+        CDiskBlockPos *me = const_cast<CDiskBlockPos*>(this);
+        if (!fRead) {
+            unsigned int nCode = (nHeight + 1) * 2 + (nAlternative > 0);
+            READWRITE(VARINT(nCode));
+            if (nAlternative > 0) {
+                unsigned int nAlt = nAlternative - 1;
+                READWRITE(VARINT(nAlt));
+            }
+        } else {
+            unsigned int nCode = 0;
+            READWRITE(VARINT(nCode));
+            me->nHeight = (nCode / 2) - 1;
+            if (nCode & 1) {
+                unsigned int nAlt = 0;
+                READWRITE(VARINT(nAlt));
+                me->nAlternative = 1 + nAlt;
+            } else {
+                me->nAlternative = 0;
+            }
+        }
+    });)
+
+    friend bool operator==(const CDiskBlockPos &a, const CDiskBlockPos &b) {
+        return ((a.nHeight == b.nHeight) && (a.nAlternative == b.nAlternative));
+    }
+
+    friend bool operator!=(const CDiskBlockPos &a, const CDiskBlockPos &b) {
+        return !(a == b);
+    }
+
+    void SetNull() { nHeight = -1; nAlternative = 0; }
+    bool IsNull() const { return ((nHeight == -1) && (nAlternative == 0)); }
+
+    void SetMemPool() { nHeight = -1; nAlternative = -1; }
+    bool IsMemPool() const { return ((nHeight == -1) && (nAlternative == -1)); }
+};
+
 /** Position on disk for a particular transaction. */
 class CDiskTxPos
 {
 public:
-    unsigned int nFile;
-    unsigned int nBlockPos;
+    CDiskBlockPos blockPos;
     unsigned int nTxPos;
 
-    CDiskTxPos()
+    CDiskTxPos(bool fInMemPool = false)
     {
         SetNull();
+        if (fInMemPool)
+            blockPos.SetMemPool();
     }
 
-    CDiskTxPos(unsigned int nFileIn, unsigned int nBlockPosIn, unsigned int nTxPosIn)
-    {
-        nFile = nFileIn;
-        nBlockPos = nBlockPosIn;
-        nTxPos = nTxPosIn;
-    }
+    CDiskTxPos(const CDiskBlockPos &block, unsigned int nTxPosIn) : blockPos(block), nTxPos(nTxPosIn) { }
 
-    IMPLEMENT_SERIALIZE( READWRITE(FLATDATA(*this)); )
-    void SetNull() { nFile = (unsigned int) -1; nBlockPos = 0; nTxPos = 0; }
-    bool IsNull() const { return (nFile == (unsigned int) -1); }
+    IMPLEMENT_SERIALIZE( 
+        READWRITE(blockPos);
+        READWRITE(VARINT(nTxPos));
+    )
+
+    void SetNull() { blockPos.SetNull(); nTxPos = 0; }
+    bool IsNull() const { return blockPos.IsNull(); }
+    bool IsMemPool() const { return blockPos.IsMemPool(); }
 
     friend bool operator==(const CDiskTxPos& a, const CDiskTxPos& b)
     {
-        return (a.nFile     == b.nFile &&
-                a.nBlockPos == b.nBlockPos &&
+        return (a.blockPos  == b.blockPos &&
                 a.nTxPos    == b.nTxPos);
     }
 
@@ -158,8 +239,10 @@ public:
     {
         if (IsNull())
             return "null";
+        else if (blockPos.IsMemPool())
+            return "mempool";
         else
-            return strprintf("(nFile=%u, nBlockPos=%u, nTxPos=%u)", nFile, nBlockPos, nTxPos);
+            return strprintf("(%s, nTxPos=%u)", blockPos.GetFileName("").string().c_str(), nTxPos);
     }
 
     void print() const
@@ -545,7 +628,7 @@ public:
 
     bool ReadFromDisk(CDiskTxPos pos, FILE** pfileRet=NULL)
     {
-        CAutoFile filein = CAutoFile(OpenBlockFile(pos.nFile, 0, pfileRet ? "rb+" : "rb"), SER_DISK, CLIENT_VERSION);
+        CAutoFile filein = CAutoFile(OpenBlockFile(pos.blockPos, pfileRet ? "rb+" : "rb"), SER_DISK, CLIENT_VERSION);
         if (!filein)
             return error("CTransaction::ReadFromDisk() : OpenBlockFile failed");
 
@@ -1215,22 +1298,15 @@ public:
     }
 
 
-    bool WriteToDisk(unsigned int& nFileRet, unsigned int& nBlockPosRet)
+    bool WriteToDisk(CDiskBlockPos &pos)
     {
         // Open history file to append
-        CAutoFile fileout = CAutoFile(AppendBlockFile(nFileRet), SER_DISK, CLIENT_VERSION);
+        pos.MakeUnique(GetDataDir());
+        CAutoFile fileout = CAutoFile(OpenBlockFile(pos, "ab"), SER_DISK, CLIENT_VERSION);
         if (!fileout)
             return error("CBlock::WriteToDisk() : AppendBlockFile failed");
 
-        // Write index header
-        unsigned int nSize = fileout.GetSerializeSize(*this);
-        fileout << FLATDATA(pchMessageStart) << nSize;
-
         // Write block
-        long fileOutPos = ftell(fileout);
-        if (fileOutPos < 0)
-            return error("CBlock::WriteToDisk() : ftell failed");
-        nBlockPosRet = fileOutPos;
         fileout << *this;
 
         // Flush stdio buffers and commit to disk before returning
@@ -1241,12 +1317,12 @@ public:
         return true;
     }
 
-    bool ReadFromDisk(unsigned int nFile, unsigned int nBlockPos, bool fReadTransactions=true)
+    bool ReadFromDisk(const CDiskBlockPos &pos, bool fReadTransactions = true)
     {
         SetNull();
 
         // Open history file to read
-        CAutoFile filein = CAutoFile(OpenBlockFile(nFile, nBlockPos, "rb"), SER_DISK, CLIENT_VERSION);
+        CAutoFile filein = CAutoFile(OpenBlockFile(pos, "rb"), SER_DISK, CLIENT_VERSION);
         if (!filein)
             return error("CBlock::ReadFromDisk() : OpenBlockFile failed");
         if (!fReadTransactions)
@@ -1294,7 +1370,7 @@ public:
     bool ConnectBlock(CTxDB& txdb, CBlockIndex* pindex, bool fJustCheck=false);
     bool ReadFromDisk(const CBlockIndex* pindex, bool fReadTransactions=true);
     bool SetBestChain(CTxDB& txdb, CBlockIndex* pindexNew);
-    bool AddToBlockIndex(unsigned int nFile, unsigned int nBlockPos);
+    bool AddToBlockIndex(const CDiskBlockPos &pos);
     bool CheckBlock(bool fCheckPOW=true, bool fCheckMerkleRoot=true) const;
     bool AcceptBlock();
 
@@ -1320,9 +1396,8 @@ public:
     const uint256* phashBlock;
     CBlockIndex* pprev;
     CBlockIndex* pnext;
-    unsigned int nFile;
-    unsigned int nBlockPos;
     int nHeight;
+    unsigned int nAlternative;
     CBigNum bnChainWork;
 
     // block header
@@ -1338,10 +1413,9 @@ public:
         phashBlock = NULL;
         pprev = NULL;
         pnext = NULL;
-        nFile = 0;
-        nBlockPos = 0;
         nHeight = 0;
         bnChainWork = 0;
+        nAlternative = 0;
 
         nVersion       = 0;
         hashMerkleRoot = 0;
@@ -1350,15 +1424,14 @@ public:
         nNonce         = 0;
     }
 
-    CBlockIndex(unsigned int nFileIn, unsigned int nBlockPosIn, CBlock& block)
+    CBlockIndex(CBlock& block)
     {
         phashBlock = NULL;
         pprev = NULL;
         pnext = NULL;
-        nFile = nFileIn;
-        nBlockPos = nBlockPosIn;
         nHeight = 0;
         bnChainWork = 0;
+        nAlternative = 0;
 
         nVersion       = block.nVersion;
         hashMerkleRoot = block.hashMerkleRoot;
@@ -1367,6 +1440,10 @@ public:
         nNonce         = block.nNonce;
     }
 
+    CDiskBlockPos GetBlockPos() const {
+        return CDiskBlockPos(nHeight, nAlternative);
+    }
+
     CBlock GetBlockHeader() const
     {
         CBlock block;
@@ -1444,11 +1521,10 @@ public:
     static bool IsSuperMajority(int minVersion, const CBlockIndex* pstart,
                                 unsigned int nRequired, unsigned int nToCheck);
 
-
     std::string ToString() const
     {
-        return strprintf("CBlockIndex(pprev=%p, pnext=%p, nFile=%u, nBlockPos=%-6u nHeight=%d, merkle=%s, hashBlock=%s)",
-            pprev, pnext, nFile, nBlockPos, nHeight,
+        return strprintf("CBlockIndex(pprev=%p, pnext=%p, nHeight=%d, merkle=%s, hashBlock=%s)",
+            pprev, pnext, nHeight,
             hashMerkleRoot.ToString().substr(0,10).c_str(),
             GetBlockHash().ToString().substr(0,20).c_str());
     }
@@ -1486,9 +1562,8 @@ public:
             READWRITE(nVersion);
 
         READWRITE(hashNext);
-        READWRITE(nFile);
-        READWRITE(nBlockPos);
         READWRITE(nHeight);
+        READWRITE(nAlternative);
 
         // block header
         READWRITE(this->nVersion);