Add optional transaction index to databases

By specifying -txindex when initializing the database, a txid-to-diskpos
index is maintained in the blktree database. This database is used to
help answering getrawtransaction() RPC queries, when enabled.

Changing the -txindex value requires a -reindex; the client will abort
at startup if the database and the specified -txindex mismatch.

src/init.cpp

@@ -305,6 +305,7 @@ std::string HelpMessage()
         "  -salvagewallet         " + _("Attempt to recover private keys from a corrupt wallet.dat") + "\n" +
         "  -checkblocks=<n>       " + _("How many blocks to check at startup (default: 2500, 0 = all)") + "\n" +
         "  -checklevel=<n>        " + _("How thorough the block verification is (0-4, default: 3)") + "\n" +
+        "  -txindex               " + _("Maintain a full transaction index (default: 0)") + "\n" +
         "  -loadblock=<file>      " + _("Imports blocks from external blk000??.dat file") + "\n" +
         "  -reindex               " + _("Rebuild blockchain index from current blk000??.dat files") + "\n" +
         "  -par=N                 " + _("Set the number of script verification threads (1-16, 0=auto, default: 0)") + "\n" +
@@ -781,7 +782,7 @@ bool AppInit2()
     if (nTotalCache < (1 << 22))
         nTotalCache = (1 << 22); // total cache cannot be less than 4 MiB
     size_t nBlockTreeDBCache = nTotalCache / 8;
-    if (nBlockTreeDBCache > (1 << 21))
+    if (nBlockTreeDBCache > (1 << 21) && !GetBoolArg("-txindex", false))
         nBlockTreeDBCache = (1 << 21); // block tree db cache shouldn't be larger than 2 MiB
     nTotalCache -= nBlockTreeDBCache;
     size_t nCoinDBCache = nTotalCache / 2; // use half of the remaining cache for coindb cache
@@ -806,6 +807,9 @@ bool AppInit2()
     if (!VerifyDB())
         return InitError(_("Corrupted block database detected. Please restart the client with -reindex."));
 
+    if (mapArgs.count("-txindex") && fTxIndex != GetBoolArg("-txindex", false))
+        return InitError(_("You need to rebuild the databases using -reindex to change -txindex"));
+
     // as LoadBlockIndex can take several minutes, it's possible the user
     // requested to kill bitcoin-qt during the last operation. If so, exit.
     // As the program has not fully started yet, Shutdown() is possibly overkill.

src/main.cpp

@@ -45,6 +45,7 @@ int nScriptCheckThreads = 0;
 bool fImporting = false;
 bool fReindex = false;
 bool fBenchmark = false;
+bool fTxIndex = false;
 unsigned int nCoinCacheSize = 5000;
 
 CMedianFilter<int> cPeerBlockCounts(8, 0); // Amount of blocks that other nodes claim to have
@@ -949,6 +950,25 @@ bool GetTransaction(const uint256 &hash, CTransaction &txOut, uint256 &hashBlock
             }
         }
 
+        if (fTxIndex) {
+            CDiskTxPos postx;
+            if (pblocktree->ReadTxIndex(hash, postx)) {
+                CAutoFile file(OpenBlockFile(postx, true), SER_DISK, CLIENT_VERSION);
+                CBlockHeader header;
+                try {
+                    file >> header;
+                    fseek(file, postx.nTxOffset, SEEK_CUR);
+                    file >> txOut;
+                } catch (std::exception &e) {
+                    return error("%s() : deserialize or I/O error", __PRETTY_FUNCTION__);
+                }
+                hashBlock = header.GetHash();
+                if (txOut.GetHash() != hash)
+                    return error("%s() : txid mismatch", __PRETTY_FUNCTION__);
+                return true;
+            }
+        }
+
         if (fAllowSlow) { // use coin database to locate block that contains transaction, and scan it
             int nHeight = -1;
             {
@@ -1632,6 +1652,9 @@ bool CBlock::ConnectBlock(CBlockIndex* pindex, CCoinsViewCache &view, bool fJust
     int64 nFees = 0;
     int nInputs = 0;
     unsigned int nSigOps = 0;
+    CDiskTxPos pos(pindex->GetBlockPos(), GetSizeOfCompactSize(vtx.size()));
+    std::vector<std::pair<uint256, CDiskTxPos> > vPos;
+    vPos.reserve(vtx.size());
     for (unsigned int i=0; i<vtx.size(); i++)
     {
 
@@ -1671,6 +1694,8 @@ bool CBlock::ConnectBlock(CBlockIndex* pindex, CCoinsViewCache &view, bool fJust
         if (!tx.IsCoinBase())
             blockundo.vtxundo.push_back(txundo);
 
+        vPos.push_back(std::make_pair(GetTxHash(i), pos));
+        pos.nTxOffset += ::GetSerializeSize(tx, SER_DISK, CLIENT_VERSION);
     }
     int64 nTime = GetTimeMicros() - nStart;
     if (fBenchmark)
@@ -1710,6 +1735,9 @@ bool CBlock::ConnectBlock(CBlockIndex* pindex, CCoinsViewCache &view, bool fJust
             return error("ConnectBlock() : WriteBlockIndex failed");
     }
 
+    if (fTxIndex)
+        pblocktree->WriteTxIndex(vPos);
+
     // add this block to the view's block chain
     if (!view.SetBestBlock(pindex))
         return false;
@@ -2554,6 +2582,10 @@ bool static LoadBlockIndexDB()
     pblocktree->ReadReindexing(fReindexing);
     fReindex |= fReindexing;
 
+    // Check whether we have a transaction index
+    pblocktree->ReadFlag("txindex", fTxIndex);
+    printf("LoadBlockIndex(): transaction index %s\n", fTxIndex ? "enabled" : "disabled");
+
     // Load hashBestChain pointer to end of best chain
     pindexBest = pcoinsTip->GetBestBlock();
     if (pindexBest == NULL)
@@ -2658,13 +2690,10 @@ bool LoadBlockIndex()
         hashGenesisBlock = uint256("000000000933ea01ad0ee984209779baaec3ced90fa3f408719526f8d77f4943");
     }
 
-    if (fReindex)
-        return true;
-
     //
     // Load block index from databases
     //
-    if (!LoadBlockIndexDB())
+    if (!fReindex && !LoadBlockIndexDB())
         return false;
 
     //
@@ -2672,6 +2701,13 @@ bool LoadBlockIndex()
     //
     if (mapBlockIndex.empty())
     {
+        fTxIndex = GetBoolArg("-txindex", false);
+        pblocktree->WriteFlag("txindex", fTxIndex);
+        printf("Initializing databases...\n");
+
+        if (fReindex)
+            return true;
+
         // Genesis Block:
         // CBlock(hash=000000000019d6, ver=1, hashPrevBlock=00000000000000, hashMerkleRoot=4a5e1e, nTime=1231006505, nBits=1d00ffff, nNonce=2083236893, vtx=1)
         //   CTransaction(hash=4a5e1e, ver=1, vin.size=1, vout.size=1, nLockTime=0)

src/main.h

@@ -93,6 +93,7 @@ extern bool fImporting;
 extern bool fReindex;
 extern bool fBenchmark;
 extern int nScriptCheckThreads;
+extern bool fTxIndex;
 extern unsigned int nCoinCacheSize;
 
 // Settings
@@ -196,9 +197,8 @@ static inline std::string BlockHashStr(const uint256& hash)
 
 bool GetWalletFile(CWallet* pwallet, std::string &strWalletFileOut);
 
-class CDiskBlockPos
+struct CDiskBlockPos
 {
-public:
     int nFile;
     unsigned int nPos;
 
@@ -228,7 +228,27 @@ public:
     bool IsNull() const { return (nFile == -1); }
 };
 
+struct CDiskTxPos : public CDiskBlockPos
+{
+    unsigned int nTxOffset; // after header
+
+    IMPLEMENT_SERIALIZE(
+        READWRITE(*(CDiskBlockPos*)this);
+        READWRITE(VARINT(nTxOffset));
+    )
+
+    CDiskTxPos(const CDiskBlockPos &blockIn, unsigned int nTxOffsetIn) : CDiskBlockPos(blockIn.nFile, blockIn.nPos), nTxOffset(nTxOffsetIn) {
+    }
+
+    CDiskTxPos() {
+        SetNull();
+    }
 
+    void SetNull() {
+        CDiskBlockPos::SetNull();
+        nTxOffset = 0;
+    }
+};
 
 
 /** An inpoint - a combination of a transaction and an index n into its vin */

src/txdb.cpp

@@ -145,6 +145,29 @@ bool CCoinsViewDB::GetStats(CCoinsStats &stats) {
     return true;
 }
 
+bool CBlockTreeDB::ReadTxIndex(const uint256 &txid, CDiskTxPos &pos) {
+    return Read(make_pair('t', txid), pos);
+}
+
+bool CBlockTreeDB::WriteTxIndex(const std::vector<std::pair<uint256, CDiskTxPos> >&vect) {
+    CLevelDBBatch batch;
+    for (std::vector<std::pair<uint256,CDiskTxPos> >::const_iterator it=vect.begin(); it!=vect.end(); it++)
+        batch.Write(make_pair('t', it->first), it->second);
+    return WriteBatch(batch);
+}
+
+bool CBlockTreeDB::WriteFlag(const std::string &name, bool fValue) {
+    return Write(std::make_pair('F', name), fValue ? '1' : '0');
+}
+
+bool CBlockTreeDB::ReadFlag(const std::string &name, bool &fValue) {
+    char ch;
+    if (!Read(std::make_pair('F', name), ch))
+        return false;
+    fValue = ch == '1';
+    return true;
+}
+
 bool CBlockTreeDB::LoadBlockIndexGuts()
 {
     leveldb::Iterator *pcursor = NewIterator();

src/txdb.h

@@ -43,6 +43,10 @@ public:
     bool WriteLastBlockFile(int nFile);
     bool WriteReindexing(bool fReindex);
     bool ReadReindexing(bool &fReindex);
+    bool ReadTxIndex(const uint256 &txid, CDiskTxPos &pos);
+    bool WriteTxIndex(const std::vector<std::pair<uint256, CDiskTxPos> > &list);
+    bool WriteFlag(const std::string &name, bool fValue);
+    bool ReadFlag(const std::string &name, bool &fValue);
     bool LoadBlockIndexGuts();
 };