Merge #13243: Make reusable base class for auxiliary indices

ec3073a274bf7affe1b8c87a10f75d126f5ac027 index: Move index DBs into index/ directory. (Jim Posen)
89eddcd365e9a2218648f5cc5b9f22b28023f50a index: Remove TxIndexDB from public interface of TxIndex. (Jim Posen)
2318affd27de436ddf9d866a4b82eed8ea2e738b MOVEONLY: Move BaseIndex to its own file. (Jim Posen)
f376a4924109af2496b5fd16a787299eb039f1c8 index: Generalize logged statements in BaseIndex. (Jim Posen)
61a1226d87d80234b2be123c5cad07534c318cfb index: Extract logic from TxIndex into reusable base class. (Jim Posen)
e5af5fc6fb4658599b940d1d50853129b31b8766 db: Make reusable base class for index databases. (Jim Posen)
9b0ec1a7f9ffae816fd5ca32ff7e7559640b6f6d db: Remove obsolete methods from CBlockTreeDB. (Jim Posen)

Pull request description:

  This refactors most of the logic in TxIndex into a reusable base class for other indices. There are two commits moving code between files, which may be be more easily reviewed using `git diff --color-moved` (https://blog.github.com/2018-04-05-git-217-released/).

  The motivation for this is to support BIP 157 by indexing block filters.

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Tree-SHA512: 0857f04df2aa920178dab2eb8e57984d8eb4d5010deca9971190358479e05b6672ccca2a08af0a7ac9fe02afb947be84cf35a3693204d0667263c6add2959cbf

9 files changed, 594 insertions, 524 deletions

diff --git a/src/Makefile.am b/src/Makefile.am
index 96e56915a6..9462c407a1 100644
--- a/src/Makefile.am
+++ b/src/Makefile.am
@@ -107,6 +107,7 @@ BITCOIN_CORE_H = \
   fs.h \
   httprpc.h \
   httpserver.h \
+  index/base.h \
   index/txindex.h \
   indirectmap.h \
   init.h \
@@ -208,6 +209,7 @@ libbitcoin_server_a_SOURCES = \
   consensus/tx_verify.cpp \
   httprpc.cpp \
   httpserver.cpp \
+  index/base.cpp \
   index/txindex.cpp \
   init.cpp \
   dbwrapper.cpp \
diff --git a/src/index/base.cpp b/src/index/base.cpp
new file mode 100644
index 0000000000..738166dc94
--- /dev/null
+++ b/src/index/base.cpp
@@ -0,0 +1,278 @@
+// Copyright (c) 2017-2018 The Bitcoin Core developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#include <chainparams.h>
+#include <index/base.h>
+#include <init.h>
+#include <tinyformat.h>
+#include <ui_interface.h>
+#include <util.h>
+#include <validation.h>
+#include <warnings.h>
+
+constexpr char DB_BEST_BLOCK = 'B';
+
+constexpr int64_t SYNC_LOG_INTERVAL = 30; // seconds
+constexpr int64_t SYNC_LOCATOR_WRITE_INTERVAL = 30; // seconds
+
+template<typename... Args>
+static void FatalError(const char* fmt, const Args&... args)
+{
+    std::string strMessage = tfm::format(fmt, args...);
+    SetMiscWarning(strMessage);
+    LogPrintf("*** %s\n", strMessage);
+    uiInterface.ThreadSafeMessageBox(
+        "Error: A fatal internal error occurred, see debug.log for details",
+        "", CClientUIInterface::MSG_ERROR);
+    StartShutdown();
+}
+
+BaseIndex::DB::DB(const fs::path& path, size_t n_cache_size, bool f_memory, bool f_wipe, bool f_obfuscate) :
+    CDBWrapper(path, n_cache_size, f_memory, f_wipe, f_obfuscate)
+{}
+
+bool BaseIndex::DB::ReadBestBlock(CBlockLocator& locator) const
+{
+    bool success = Read(DB_BEST_BLOCK, locator);
+    if (!success) {
+        locator.SetNull();
+    }
+    return success;
+}
+
+bool BaseIndex::DB::WriteBestBlock(const CBlockLocator& locator)
+{
+    return Write(DB_BEST_BLOCK, locator);
+}
+
+BaseIndex::~BaseIndex()
+{
+    Interrupt();
+    Stop();
+}
+
+bool BaseIndex::Init()
+{
+    CBlockLocator locator;
+    if (!GetDB().ReadBestBlock(locator)) {
+        locator.SetNull();
+    }
+
+    LOCK(cs_main);
+    m_best_block_index = FindForkInGlobalIndex(chainActive, locator);
+    m_synced = m_best_block_index.load() == chainActive.Tip();
+    return true;
+}
+
+static const CBlockIndex* NextSyncBlock(const CBlockIndex* pindex_prev)
+{
+    AssertLockHeld(cs_main);
+
+    if (!pindex_prev) {
+        return chainActive.Genesis();
+    }
+
+    const CBlockIndex* pindex = chainActive.Next(pindex_prev);
+    if (pindex) {
+        return pindex;
+    }
+
+    return chainActive.Next(chainActive.FindFork(pindex_prev));
+}
+
+void BaseIndex::ThreadSync()
+{
+    const CBlockIndex* pindex = m_best_block_index.load();
+    if (!m_synced) {
+        auto& consensus_params = Params().GetConsensus();
+
+        int64_t last_log_time = 0;
+        int64_t last_locator_write_time = 0;
+        while (true) {
+            if (m_interrupt) {
+                WriteBestBlock(pindex);
+                return;
+            }
+
+            {
+                LOCK(cs_main);
+                const CBlockIndex* pindex_next = NextSyncBlock(pindex);
+                if (!pindex_next) {
+                    WriteBestBlock(pindex);
+                    m_best_block_index = pindex;
+                    m_synced = true;
+                    break;
+                }
+                pindex = pindex_next;
+            }
+
+            int64_t current_time = GetTime();
+            if (last_log_time + SYNC_LOG_INTERVAL < current_time) {
+                LogPrintf("Syncing %s with block chain from height %d\n",
+                          GetName(), pindex->nHeight);
+                last_log_time = current_time;
+            }
+
+            if (last_locator_write_time + SYNC_LOCATOR_WRITE_INTERVAL < current_time) {
+                WriteBestBlock(pindex);
+                last_locator_write_time = current_time;
+            }
+
+            CBlock block;
+            if (!ReadBlockFromDisk(block, pindex, consensus_params)) {
+                FatalError("%s: Failed to read block %s from disk",
+                           __func__, pindex->GetBlockHash().ToString());
+                return;
+            }
+            if (!WriteBlock(block, pindex)) {
+                FatalError("%s: Failed to write block %s to index database",
+                           __func__, pindex->GetBlockHash().ToString());
+                return;
+            }
+        }
+    }
+
+    if (pindex) {
+        LogPrintf("%s is enabled at height %d\n", GetName(), pindex->nHeight);
+    } else {
+        LogPrintf("%s is enabled\n", GetName());
+    }
+}
+
+bool BaseIndex::WriteBestBlock(const CBlockIndex* block_index)
+{
+    LOCK(cs_main);
+    if (!GetDB().WriteBestBlock(chainActive.GetLocator(block_index))) {
+        return error("%s: Failed to write locator to disk", __func__);
+    }
+    return true;
+}
+
+void BaseIndex::BlockConnected(const std::shared_ptr<const CBlock>& block, const CBlockIndex* pindex,
+                               const std::vector<CTransactionRef>& txn_conflicted)
+{
+    if (!m_synced) {
+        return;
+    }
+
+    const CBlockIndex* best_block_index = m_best_block_index.load();
+    if (!best_block_index) {
+        if (pindex->nHeight != 0) {
+            FatalError("%s: First block connected is not the genesis block (height=%d)",
+                       __func__, pindex->nHeight);
+            return;
+        }
+    } else {
+        // Ensure block connects to an ancestor of the current best block. This should be the case
+        // most of the time, but may not be immediately after the sync thread catches up and sets
+        // m_synced. Consider the case where there is a reorg and the blocks on the stale branch are
+        // in the ValidationInterface queue backlog even after the sync thread has caught up to the
+        // new chain tip. In this unlikely event, log a warning and let the queue clear.
+        if (best_block_index->GetAncestor(pindex->nHeight - 1) != pindex->pprev) {
+            LogPrintf("%s: WARNING: Block %s does not connect to an ancestor of " /* Continued */
+                      "known best chain (tip=%s); not updating index\n",
+                      __func__, pindex->GetBlockHash().ToString(),
+                      best_block_index->GetBlockHash().ToString());
+            return;
+        }
+    }
+
+    if (WriteBlock(*block, pindex)) {
+        m_best_block_index = pindex;
+    } else {
+        FatalError("%s: Failed to write block %s to index",
+                   __func__, pindex->GetBlockHash().ToString());
+        return;
+    }
+}
+
+void BaseIndex::ChainStateFlushed(const CBlockLocator& locator)
+{
+    if (!m_synced) {
+        return;
+    }
+
+    const uint256& locator_tip_hash = locator.vHave.front();
+    const CBlockIndex* locator_tip_index;
+    {
+        LOCK(cs_main);
+        locator_tip_index = LookupBlockIndex(locator_tip_hash);
+    }
+
+    if (!locator_tip_index) {
+        FatalError("%s: First block (hash=%s) in locator was not found",
+                   __func__, locator_tip_hash.ToString());
+        return;
+    }
+
+    // This checks that ChainStateFlushed callbacks are received after BlockConnected. The check may fail
+    // immediately after the sync thread catches up and sets m_synced. Consider the case where
+    // there is a reorg and the blocks on the stale branch are in the ValidationInterface queue
+    // backlog even after the sync thread has caught up to the new chain tip. In this unlikely
+    // event, log a warning and let the queue clear.
+    const CBlockIndex* best_block_index = m_best_block_index.load();
+    if (best_block_index->GetAncestor(locator_tip_index->nHeight) != locator_tip_index) {
+        LogPrintf("%s: WARNING: Locator contains block (hash=%s) not on known best " /* Continued */
+                  "chain (tip=%s); not writing index locator\n",
+                  __func__, locator_tip_hash.ToString(),
+                  best_block_index->GetBlockHash().ToString());
+        return;
+    }
+
+    if (!GetDB().WriteBestBlock(locator)) {
+        error("%s: Failed to write locator to disk", __func__);
+    }
+}
+
+bool BaseIndex::BlockUntilSyncedToCurrentChain()
+{
+    AssertLockNotHeld(cs_main);
+
+    if (!m_synced) {
+        return false;
+    }
+
+    {
+        // Skip the queue-draining stuff if we know we're caught up with
+        // chainActive.Tip().
+        LOCK(cs_main);
+        const CBlockIndex* chain_tip = chainActive.Tip();
+        const CBlockIndex* best_block_index = m_best_block_index.load();
+        if (best_block_index->GetAncestor(chain_tip->nHeight) == chain_tip) {
+            return true;
+        }
+    }
+
+    LogPrintf("%s: %s is catching up on block notifications\n", __func__, GetName());
+    SyncWithValidationInterfaceQueue();
+    return true;
+}
+
+void BaseIndex::Interrupt()
+{
+    m_interrupt();
+}
+
+void BaseIndex::Start()
+{
+    // Need to register this ValidationInterface before running Init(), so that
+    // callbacks are not missed if Init sets m_synced to true.
+    RegisterValidationInterface(this);
+    if (!Init()) {
+        FatalError("%s: %s failed to initialize", __func__, GetName());
+        return;
+    }
+
+    m_thread_sync = std::thread(&TraceThread<std::function<void()>>, GetName(),
+                                std::bind(&BaseIndex::ThreadSync, this));
+}
+
+void BaseIndex::Stop()
+{
+    UnregisterValidationInterface(this);
+
+    if (m_thread_sync.joinable()) {
+        m_thread_sync.join();
+    }
+}
diff --git a/src/index/base.h b/src/index/base.h
new file mode 100644
index 0000000000..04ee6e6cc2
--- /dev/null
+++ b/src/index/base.h
@@ -0,0 +1,98 @@
+// Copyright (c) 2017-2018 The Bitcoin Core developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#ifndef BITCOIN_INDEX_BASE_H
+#define BITCOIN_INDEX_BASE_H
+
+#include <dbwrapper.h>
+#include <primitives/block.h>
+#include <primitives/transaction.h>
+#include <threadinterrupt.h>
+#include <uint256.h>
+#include <validationinterface.h>
+
+class CBlockIndex;
+
+/**
+ * Base class for indices of blockchain data. This implements
+ * CValidationInterface and ensures blocks are indexed sequentially according
+ * to their position in the active chain.
+ */
+class BaseIndex : public CValidationInterface
+{
+protected:
+    class DB : public CDBWrapper
+    {
+    public:
+        DB(const fs::path& path, size_t n_cache_size,
+           bool f_memory = false, bool f_wipe = false, bool f_obfuscate = false);
+
+        /// Read block locator of the chain that the txindex is in sync with.
+        bool ReadBestBlock(CBlockLocator& locator) const;
+
+        /// Write block locator of the chain that the txindex is in sync with.
+        bool WriteBestBlock(const CBlockLocator& locator);
+    };
+
+private:
+    /// Whether the index is in sync with the main chain. The flag is flipped
+    /// from false to true once, after which point this starts processing
+    /// ValidationInterface notifications to stay in sync.
+    std::atomic<bool> m_synced{false};
+
+    /// The last block in the chain that the index is in sync with.
+    std::atomic<const CBlockIndex*> m_best_block_index{nullptr};
+
+    std::thread m_thread_sync;
+    CThreadInterrupt m_interrupt;
+
+    /// Sync the index with the block index starting from the current best block.
+    /// Intended to be run in its own thread, m_thread_sync, and can be
+    /// interrupted with m_interrupt. Once the index gets in sync, the m_synced
+    /// flag is set and the BlockConnected ValidationInterface callback takes
+    /// over and the sync thread exits.
+    void ThreadSync();
+
+    /// Write the current chain block locator to the DB.
+    bool WriteBestBlock(const CBlockIndex* block_index);
+
+protected:
+    void BlockConnected(const std::shared_ptr<const CBlock>& block, const CBlockIndex* pindex,
+                        const std::vector<CTransactionRef>& txn_conflicted) override;
+
+    void ChainStateFlushed(const CBlockLocator& locator) override;
+
+    /// Initialize internal state from the database and block index.
+    virtual bool Init();
+
+    /// Write update index entries for a newly connected block.
+    virtual bool WriteBlock(const CBlock& block, const CBlockIndex* pindex) { return true; }
+
+    virtual DB& GetDB() const = 0;
+
+    /// Get the name of the index for display in logs.
+    virtual const char* GetName() const = 0;
+
+public:
+    /// Destructor interrupts sync thread if running and blocks until it exits.
+    virtual ~BaseIndex();
+
+    /// Blocks the current thread until the index is caught up to the current
+    /// state of the block chain. This only blocks if the index has gotten in
+    /// sync once and only needs to process blocks in the ValidationInterface
+    /// queue. If the index is catching up from far behind, this method does
+    /// not block and immediately returns false.
+    bool BlockUntilSyncedToCurrentChain();
+
+    void Interrupt();
+
+    /// Start initializes the sync state and registers the instance as a
+    /// ValidationInterface so that it stays in sync with blockchain updates.
+    void Start();
+
+    /// Stops the instance from staying in sync with blockchain updates.
+    void Stop();
+};
+
+#endif // BITCOIN_INDEX_BASE_H
diff --git a/src/index/txindex.cpp b/src/index/txindex.cpp
index 3ff16b7664..e106b9b420 100644
--- a/src/index/txindex.cpp
+++ b/src/index/txindex.cpp
@@ -2,258 +2,261 @@
 // Distributed under the MIT software license, see the accompanying
 // file COPYING or http://www.opensource.org/licenses/mit-license.php.
 
-#include <chainparams.h>
 #include <index/txindex.h>
 #include <init.h>
-#include <tinyformat.h>
 #include <ui_interface.h>
 #include <util.h>
 #include <validation.h>
-#include <warnings.h>
 
-constexpr int64_t SYNC_LOG_INTERVAL = 30; // seconds
-constexpr int64_t SYNC_LOCATOR_WRITE_INTERVAL = 30; // seconds
+#include <boost/thread.hpp>
+
+constexpr char DB_BEST_BLOCK = 'B';
+constexpr char DB_TXINDEX = 't';
+constexpr char DB_TXINDEX_BLOCK = 'T';
 
 std::unique_ptr<TxIndex> g_txindex;
 
-template<typename... Args>
-static void FatalError(const char* fmt, const Args&... args)
+struct CDiskTxPos : public CDiskBlockPos
 {
-    std::string strMessage = tfm::format(fmt, args...);
-    SetMiscWarning(strMessage);
-    LogPrintf("*** %s\n", strMessage);
-    uiInterface.ThreadSafeMessageBox(
-        "Error: A fatal internal error occurred, see debug.log for details",
-        "", CClientUIInterface::MSG_ERROR);
-    StartShutdown();
-}
+    unsigned int nTxOffset; // after header
 
-TxIndex::TxIndex(std::unique_ptr<TxIndexDB> db) :
-    m_db(std::move(db)), m_synced(false), m_best_block_index(nullptr)
-{}
+    ADD_SERIALIZE_METHODS;
 
-TxIndex::~TxIndex()
-{
-    Interrupt();
-    Stop();
-}
-
-bool TxIndex::Init()
-{
-    LOCK(cs_main);
-
-    // Attempt to migrate txindex from the old database to the new one. Even if
-    // chain_tip is null, the node could be reindexing and we still want to
-    // delete txindex records in the old database.
-    if (!m_db->MigrateData(*pblocktree, chainActive.GetLocator())) {
-        return false;
+    template <typename Stream, typename Operation>
+    inline void SerializationOp(Stream& s, Operation ser_action) {
+        READWRITEAS(CDiskBlockPos, *this);
+        READWRITE(VARINT(nTxOffset));
     }
 
-    CBlockLocator locator;
-    if (!m_db->ReadBestBlock(locator)) {
-        locator.SetNull();
+    CDiskTxPos(const CDiskBlockPos &blockIn, unsigned int nTxOffsetIn) : CDiskBlockPos(blockIn.nFile, blockIn.nPos), nTxOffset(nTxOffsetIn) {
     }
 
-    m_best_block_index = FindForkInGlobalIndex(chainActive, locator);
-    m_synced = m_best_block_index.load() == chainActive.Tip();
-    return true;
-}
-
-static const CBlockIndex* NextSyncBlock(const CBlockIndex* pindex_prev)
-{
-    AssertLockHeld(cs_main);
-
-    if (!pindex_prev) {
-        return chainActive.Genesis();
+    CDiskTxPos() {
+        SetNull();
     }
 
-    const CBlockIndex* pindex = chainActive.Next(pindex_prev);
-    if (pindex) {
-        return pindex;
+    void SetNull() {
+        CDiskBlockPos::SetNull();
+        nTxOffset = 0;
     }
-
-    return chainActive.Next(chainActive.FindFork(pindex_prev));
-}
-
-void TxIndex::ThreadSync()
+};
+
+/**
+ * Access to the txindex database (indexes/txindex/)
+ *
+ * The database stores a block locator of the chain the database is synced to
+ * so that the TxIndex can efficiently determine the point it last stopped at.
+ * A locator is used instead of a simple hash of the chain tip because blocks
+ * and block index entries may not be flushed to disk until after this database
+ * is updated.
+ */
+class TxIndex::DB : public BaseIndex::DB
 {
-    const CBlockIndex* pindex = m_best_block_index.load();
-    if (!m_synced) {
-        auto& consensus_params = Params().GetConsensus();
-
-        int64_t last_log_time = 0;
-        int64_t last_locator_write_time = 0;
-        while (true) {
-            if (m_interrupt) {
-                WriteBestBlock(pindex);
-                return;
-            }
+public:
+    explicit DB(size_t n_cache_size, bool f_memory = false, bool f_wipe = false);
 
-            {
-                LOCK(cs_main);
-                const CBlockIndex* pindex_next = NextSyncBlock(pindex);
-                if (!pindex_next) {
-                    WriteBestBlock(pindex);
-                    m_best_block_index = pindex;
-                    m_synced = true;
-                    break;
-                }
-                pindex = pindex_next;
-            }
+    /// Read the disk location of the transaction data with the given hash. Returns false if the
+    /// transaction hash is not indexed.
+    bool ReadTxPos(const uint256& txid, CDiskTxPos& pos) const;
 
-            int64_t current_time = GetTime();
-            if (last_log_time + SYNC_LOG_INTERVAL < current_time) {
-                LogPrintf("Syncing txindex with block chain from height %d\n", pindex->nHeight);
-                last_log_time = current_time;
-            }
+    /// Write a batch of transaction positions to the DB.
+    bool WriteTxs(const std::vector<std::pair<uint256, CDiskTxPos>>& v_pos);
 
-            if (last_locator_write_time + SYNC_LOCATOR_WRITE_INTERVAL < current_time) {
-                WriteBestBlock(pindex);
-                last_locator_write_time = current_time;
-            }
+    /// Migrate txindex data from the block tree DB, where it may be for older nodes that have not
+    /// been upgraded yet to the new database.
+    bool MigrateData(CBlockTreeDB& block_tree_db, const CBlockLocator& best_locator);
+};
 
-            CBlock block;
-            if (!ReadBlockFromDisk(block, pindex, consensus_params)) {
-                FatalError("%s: Failed to read block %s from disk",
-                           __func__, pindex->GetBlockHash().ToString());
-                return;
-            }
-            if (!WriteBlock(block, pindex)) {
-                FatalError("%s: Failed to write block %s to tx index database",
-                           __func__, pindex->GetBlockHash().ToString());
-                return;
-            }
-        }
-    }
+TxIndex::DB::DB(size_t n_cache_size, bool f_memory, bool f_wipe) :
+    BaseIndex::DB(GetDataDir() / "indexes" / "txindex", n_cache_size, f_memory, f_wipe)
+{}
 
-    if (pindex) {
-        LogPrintf("txindex is enabled at height %d\n", pindex->nHeight);
-    } else {
-        LogPrintf("txindex is enabled\n");
-    }
+bool TxIndex::DB::ReadTxPos(const uint256 &txid, CDiskTxPos& pos) const
+{
+    return Read(std::make_pair(DB_TXINDEX, txid), pos);
 }
 
-bool TxIndex::WriteBlock(const CBlock& block, const CBlockIndex* pindex)
+bool TxIndex::DB::WriteTxs(const std::vector<std::pair<uint256, CDiskTxPos>>& v_pos)
 {
-    CDiskTxPos pos(pindex->GetBlockPos(), GetSizeOfCompactSize(block.vtx.size()));
-    std::vector<std::pair<uint256, CDiskTxPos>> vPos;
-    vPos.reserve(block.vtx.size());
-    for (const auto& tx : block.vtx) {
-        vPos.emplace_back(tx->GetHash(), pos);
-        pos.nTxOffset += ::GetSerializeSize(*tx, SER_DISK, CLIENT_VERSION);
+    CDBBatch batch(*this);
+    for (const auto& tuple : v_pos) {
+        batch.Write(std::make_pair(DB_TXINDEX, tuple.first), tuple.second);
     }
-    return m_db->WriteTxs(vPos);
+    return WriteBatch(batch);
 }
 
-bool TxIndex::WriteBestBlock(const CBlockIndex* block_index)
+/*
+ * Safely persist a transfer of data from the old txindex database to the new one, and compact the
+ * range of keys updated. This is used internally by MigrateData.
+ */
+static void WriteTxIndexMigrationBatches(CDBWrapper& newdb, CDBWrapper& olddb,
+                                         CDBBatch& batch_newdb, CDBBatch& batch_olddb,
+                                         const std::pair<unsigned char, uint256>& begin_key,
+                                         const std::pair<unsigned char, uint256>& end_key)
 {
-    LOCK(cs_main);
-    if (!m_db->WriteBestBlock(chainActive.GetLocator(block_index))) {
-        return error("%s: Failed to write locator to disk", __func__);
-    }
-    return true;
+    // Sync new DB changes to disk before deleting from old DB.
+    newdb.WriteBatch(batch_newdb, /*fSync=*/ true);
+    olddb.WriteBatch(batch_olddb);
+    olddb.CompactRange(begin_key, end_key);
+
+    batch_newdb.Clear();
+    batch_olddb.Clear();
 }
 
-void TxIndex::BlockConnected(const std::shared_ptr<const CBlock>& block, const CBlockIndex* pindex,
-                    const std::vector<CTransactionRef>& txn_conflicted)
+bool TxIndex::DB::MigrateData(CBlockTreeDB& block_tree_db, const CBlockLocator& best_locator)
 {
-    if (!m_synced) {
-        return;
-    }
-
-    const CBlockIndex* best_block_index = m_best_block_index.load();
-    if (!best_block_index) {
-        if (pindex->nHeight != 0) {
-            FatalError("%s: First block connected is not the genesis block (height=%d)",
-                       __func__, pindex->nHeight);
-            return;
+    // The prior implementation of txindex was always in sync with block index
+    // and presence was indicated with a boolean DB flag. If the flag is set,
+    // this means the txindex from a previous version is valid and in sync with
+    // the chain tip. The first step of the migration is to unset the flag and
+    // write the chain hash to a separate key, DB_TXINDEX_BLOCK. After that, the
+    // index entries are copied over in batches to the new database. Finally,
+    // DB_TXINDEX_BLOCK is erased from the old database and the block hash is
+    // written to the new database.
+    //
+    // Unsetting the boolean flag ensures that if the node is downgraded to a
+    // previous version, it will not see a corrupted, partially migrated index
+    // -- it will see that the txindex is disabled. When the node is upgraded
+    // again, the migration will pick up where it left off and sync to the block
+    // with hash DB_TXINDEX_BLOCK.
+    bool f_legacy_flag = false;
+    block_tree_db.ReadFlag("txindex", f_legacy_flag);
+    if (f_legacy_flag) {
+        if (!block_tree_db.Write(DB_TXINDEX_BLOCK, best_locator)) {
+            return error("%s: cannot write block indicator", __func__);
         }
-    } else {
-        // Ensure block connects to an ancestor of the current best block. This should be the case
-        // most of the time, but may not be immediately after the sync thread catches up and sets
-        // m_synced. Consider the case where there is a reorg and the blocks on the stale branch are
-        // in the ValidationInterface queue backlog even after the sync thread has caught up to the
-        // new chain tip. In this unlikely event, log a warning and let the queue clear.
-        if (best_block_index->GetAncestor(pindex->nHeight - 1) != pindex->pprev) {
-            LogPrintf("%s: WARNING: Block %s does not connect to an ancestor of " /* Continued */
-                      "known best chain (tip=%s); not updating txindex\n",
-                      __func__, pindex->GetBlockHash().ToString(),
-                      best_block_index->GetBlockHash().ToString());
-            return;
+        if (!block_tree_db.WriteFlag("txindex", false)) {
+            return error("%s: cannot write block index db flag", __func__);
         }
     }
 
-    if (WriteBlock(*block, pindex)) {
-        m_best_block_index = pindex;
-    } else {
-        FatalError("%s: Failed to write block %s to txindex",
-                   __func__, pindex->GetBlockHash().ToString());
-        return;
+    CBlockLocator locator;
+    if (!block_tree_db.Read(DB_TXINDEX_BLOCK, locator)) {
+        return true;
     }
-}
 
-void TxIndex::ChainStateFlushed(const CBlockLocator& locator)
-{
-    if (!m_synced) {
-        return;
-    }
+    int64_t count = 0;
+    LogPrintf("Upgrading txindex database... [0%%]\n");
+    uiInterface.ShowProgress(_("Upgrading txindex database"), 0, true);
+    int report_done = 0;
+    const size_t batch_size = 1 << 24; // 16 MiB
+
+    CDBBatch batch_newdb(*this);
+    CDBBatch batch_olddb(block_tree_db);
+
+    std::pair<unsigned char, uint256> key;
+    std::pair<unsigned char, uint256> begin_key{DB_TXINDEX, uint256()};
+    std::pair<unsigned char, uint256> prev_key = begin_key;
+
+    bool interrupted = false;
+    std::unique_ptr<CDBIterator> cursor(block_tree_db.NewIterator());
+    for (cursor->Seek(begin_key); cursor->Valid(); cursor->Next()) {
+        boost::this_thread::interruption_point();
+        if (ShutdownRequested()) {
+            interrupted = true;
+            break;
+        }
 
-    const uint256& locator_tip_hash = locator.vHave.front();
-    const CBlockIndex* locator_tip_index;
-    {
-        LOCK(cs_main);
-        locator_tip_index = LookupBlockIndex(locator_tip_hash);
-    }
+        if (!cursor->GetKey(key)) {
+            return error("%s: cannot get key from valid cursor", __func__);
+        }
+        if (key.first != DB_TXINDEX) {
+            break;
+        }
 
-    if (!locator_tip_index) {
-        FatalError("%s: First block (hash=%s) in locator was not found",
-                   __func__, locator_tip_hash.ToString());
-        return;
+        // Log progress every 10%.
+        if (++count % 256 == 0) {
+            // Since txids are uniformly random and traversed in increasing order, the high 16 bits
+            // of the hash can be used to estimate the current progress.
+            const uint256& txid = key.second;
+            uint32_t high_nibble =
+                (static_cast<uint32_t>(*(txid.begin() + 0)) << 8) +
+                (static_cast<uint32_t>(*(txid.begin() + 1)) << 0);
+            int percentage_done = (int)(high_nibble * 100.0 / 65536.0 + 0.5);
+
+            uiInterface.ShowProgress(_("Upgrading txindex database"), percentage_done, true);
+            if (report_done < percentage_done/10) {
+                LogPrintf("Upgrading txindex database... [%d%%]\n", percentage_done);
+                report_done = percentage_done/10;
+            }
+        }
+
+        CDiskTxPos value;
+        if (!cursor->GetValue(value)) {
+            return error("%s: cannot parse txindex record", __func__);
+        }
+        batch_newdb.Write(key, value);
+        batch_olddb.Erase(key);
+
+        if (batch_newdb.SizeEstimate() > batch_size || batch_olddb.SizeEstimate() > batch_size) {
+            // NOTE: it's OK to delete the key pointed at by the current DB cursor while iterating
+            // because LevelDB iterators are guaranteed to provide a consistent view of the
+            // underlying data, like a lightweight snapshot.
+            WriteTxIndexMigrationBatches(*this, block_tree_db,
+                                         batch_newdb, batch_olddb,
+                                         prev_key, key);
+            prev_key = key;
+        }
     }
 
-    // This checks that ChainStateFlushed callbacks are received after BlockConnected. The check may fail
-    // immediately after the sync thread catches up and sets m_synced. Consider the case where
-    // there is a reorg and the blocks on the stale branch are in the ValidationInterface queue
-    // backlog even after the sync thread has caught up to the new chain tip. In this unlikely
-    // event, log a warning and let the queue clear.
-    const CBlockIndex* best_block_index = m_best_block_index.load();
-    if (best_block_index->GetAncestor(locator_tip_index->nHeight) != locator_tip_index) {
-        LogPrintf("%s: WARNING: Locator contains block (hash=%s) not on known best " /* Continued */
-                  "chain (tip=%s); not writing txindex locator\n",
-                  __func__, locator_tip_hash.ToString(),
-                  best_block_index->GetBlockHash().ToString());
-        return;
+    // If these final DB batches complete the migration, write the best block
+    // hash marker to the new database and delete from the old one. This signals
+    // that the former is fully caught up to that point in the blockchain and
+    // that all txindex entries have been removed from the latter.
+    if (!interrupted) {
+        batch_olddb.Erase(DB_TXINDEX_BLOCK);
+        batch_newdb.Write(DB_BEST_BLOCK, locator);
     }
 
-    if (!m_db->WriteBestBlock(locator)) {
-        error("%s: Failed to write locator to disk", __func__);
+    WriteTxIndexMigrationBatches(*this, block_tree_db,
+                                 batch_newdb, batch_olddb,
+                                 begin_key, key);
+
+    if (interrupted) {
+        LogPrintf("[CANCELLED].\n");
+        return false;
     }
+
+    uiInterface.ShowProgress("", 100, false);
+
+    LogPrintf("[DONE].\n");
+    return true;
 }
 
-bool TxIndex::BlockUntilSyncedToCurrentChain()
+TxIndex::TxIndex(size_t n_cache_size, bool f_memory, bool f_wipe)
+    : m_db(MakeUnique<TxIndex::DB>(n_cache_size, f_memory, f_wipe))
+{}
+
+TxIndex::~TxIndex() {}
+
+bool TxIndex::Init()
 {
-    AssertLockNotHeld(cs_main);
+    LOCK(cs_main);
 
-    if (!m_synced) {
+    // Attempt to migrate txindex from the old database to the new one. Even if
+    // chain_tip is null, the node could be reindexing and we still want to
+    // delete txindex records in the old database.
+    if (!m_db->MigrateData(*pblocktree, chainActive.GetLocator())) {
         return false;
     }
 
-    {
-        // Skip the queue-draining stuff if we know we're caught up with
-        // chainActive.Tip().
-        LOCK(cs_main);
-        const CBlockIndex* chain_tip = chainActive.Tip();
-        const CBlockIndex* best_block_index = m_best_block_index.load();
-        if (best_block_index->GetAncestor(chain_tip->nHeight) == chain_tip) {
-            return true;
-        }
-    }
+    return BaseIndex::Init();
+}
 
-    LogPrintf("%s: txindex is catching up on block notifications\n", __func__);
-    SyncWithValidationInterfaceQueue();
-    return true;
+bool TxIndex::WriteBlock(const CBlock& block, const CBlockIndex* pindex)
+{
+    CDiskTxPos pos(pindex->GetBlockPos(), GetSizeOfCompactSize(block.vtx.size()));
+    std::vector<std::pair<uint256, CDiskTxPos>> vPos;
+    vPos.reserve(block.vtx.size());
+    for (const auto& tx : block.vtx) {
+        vPos.emplace_back(tx->GetHash(), pos);
+        pos.nTxOffset += ::GetSerializeSize(*tx, SER_DISK, CLIENT_VERSION);
+    }
+    return m_db->WriteTxs(vPos);
 }
 
+BaseIndex::DB& TxIndex::GetDB() const { return *m_db; }
+
 bool TxIndex::FindTx(const uint256& tx_hash, uint256& block_hash, CTransactionRef& tx) const
 {
     CDiskTxPos postx;
@@ -281,31 +284,3 @@ bool TxIndex::FindTx(const uint256& tx_hash, uint256& block_hash, CTransactionRe
     block_hash = header.GetHash();
     return true;
 }
-
-void TxIndex::Interrupt()
-{
-    m_interrupt();
-}
-
-void TxIndex::Start()
-{
-    // Need to register this ValidationInterface before running Init(), so that
-    // callbacks are not missed if Init sets m_synced to true.
-    RegisterValidationInterface(this);
-    if (!Init()) {
-        FatalError("%s: txindex failed to initialize", __func__);
-        return;
-    }
-
-    m_thread_sync = std::thread(&TraceThread<std::function<void()>>, "txindex",
-                                std::bind(&TxIndex::ThreadSync, this));
-}
-
-void TxIndex::Stop()
-{
-    UnregisterValidationInterface(this);
-
-    if (m_thread_sync.joinable()) {
-        m_thread_sync.join();
-    }
-}
diff --git a/src/index/txindex.h b/src/index/txindex.h
index 4937bd64e9..8202c3c951 100644
--- a/src/index/txindex.h
+++ b/src/index/txindex.h
@@ -5,70 +5,39 @@
 #ifndef BITCOIN_INDEX_TXINDEX_H
 #define BITCOIN_INDEX_TXINDEX_H
 
-#include <primitives/block.h>
-#include <primitives/transaction.h>
-#include <threadinterrupt.h>
+#include <chain.h>
+#include <index/base.h>
 #include <txdb.h>
-#include <uint256.h>
-#include <validationinterface.h>
-
-class CBlockIndex;
 
 /**
  * TxIndex is used to look up transactions included in the blockchain by hash.
  * The index is written to a LevelDB database and records the filesystem
  * location of each transaction by transaction hash.
  */
-class TxIndex final : public CValidationInterface
+class TxIndex final : public BaseIndex
 {
-private:
-    const std::unique_ptr<TxIndexDB> m_db;
-
-    /// Whether the index is in sync with the main chain. The flag is flipped
-    /// from false to true once, after which point this starts processing
-    /// ValidationInterface notifications to stay in sync.
-    std::atomic<bool> m_synced;
-
-    /// The last block in the chain that the TxIndex is in sync with.
-    std::atomic<const CBlockIndex*> m_best_block_index;
-
-    std::thread m_thread_sync;
-    CThreadInterrupt m_interrupt;
-
-    /// Initialize internal state from the database and block index.
-    bool Init();
+protected:
+    class DB;
 
-    /// Sync the tx index with the block index starting from the current best
-    /// block. Intended to be run in its own thread, m_thread_sync, and can be
-    /// interrupted with m_interrupt. Once the txindex gets in sync, the
-    /// m_synced flag is set and the BlockConnected ValidationInterface callback
-    /// takes over and the sync thread exits.
-    void ThreadSync();
+private:
+    const std::unique_ptr<DB> m_db;
 
-    /// Write update index entries for a newly connected block.
-    bool WriteBlock(const CBlock& block, const CBlockIndex* pindex);
+protected:
+    /// Override base class init to migrate from old database.
+    bool Init() override;
 
-    /// Write the current chain block locator to the DB.
-    bool WriteBestBlock(const CBlockIndex* block_index);
+    bool WriteBlock(const CBlock& block, const CBlockIndex* pindex) override;
 
-protected:
-    void BlockConnected(const std::shared_ptr<const CBlock>& block, const CBlockIndex* pindex,
-                        const std::vector<CTransactionRef>& txn_conflicted) override;
+    BaseIndex::DB& GetDB() const override;
 
-    void ChainStateFlushed(const CBlockLocator& locator) override;
+    const char* GetName() const override { return "txindex"; }
 
 public:
-    /// Constructs the TxIndex, which becomes available to be queried.
-    explicit TxIndex(std::unique_ptr<TxIndexDB> db);
-
-    /// Destructor interrupts sync thread if running and blocks until it exits.
-    ~TxIndex();
+    /// Constructs the index, which becomes available to be queried.
+    explicit TxIndex(size_t n_cache_size, bool f_memory = false, bool f_wipe = false);
 
-    /// Blocks the current thread until the transaction index is caught up to
-    /// the current state of the block chain. This only blocks if the index has gotten in sync once
-    /// and only needs to process blocks in the ValidationInterface queue. If the index is catching
-    /// up from far behind, this method does not block and immediately returns false.
-    bool BlockUntilSyncedToCurrentChain();
+    // Destructor is declared because this class contains a unique_ptr to an incomplete type.
+    virtual ~TxIndex() override;
 
     /// Look up a transaction by hash.
     ///
@@ -77,15 +46,6 @@ public:
     /// @param[out]  tx  The transaction itself.
     /// @return  true if transaction is found, false otherwise
     bool FindTx(const uint256& tx_hash, uint256& block_hash, CTransactionRef& tx) const;
-
-    void Interrupt();
-
-    /// Start initializes the sync state and registers the instance as a
-    /// ValidationInterface so that it stays in sync with blockchain updates.
-    void Start();
-
-    /// Stops the instance from staying in sync with blockchain updates.
-    void Stop();
 };
 
 /// The global transaction index, used in GetTransaction. May be null.
diff --git a/src/init.cpp b/src/init.cpp
index b4e2eec0d2..9246f6e71c 100644
--- a/src/init.cpp
+++ b/src/init.cpp
@@ -1606,8 +1606,7 @@ bool AppInitMain()
 
     // ********************************************************* Step 8: start indexers
     if (gArgs.GetBoolArg("-txindex", DEFAULT_TXINDEX)) {
-        auto txindex_db = MakeUnique<TxIndexDB>(nTxIndexCache, false, fReindex);
-        g_txindex = MakeUnique<TxIndex>(std::move(txindex_db));
+        g_txindex = MakeUnique<TxIndex>(nTxIndexCache, false, fReindex);
         g_txindex->Start();
     }
 
diff --git a/src/test/txindex_tests.cpp b/src/test/txindex_tests.cpp
index 14158f2875..be7ee2428b 100644
--- a/src/test/txindex_tests.cpp
+++ b/src/test/txindex_tests.cpp
@@ -15,7 +15,7 @@ BOOST_AUTO_TEST_SUITE(txindex_tests)
 
 BOOST_FIXTURE_TEST_CASE(txindex_initial_sync, TestChain100Setup)
 {
-    TxIndex txindex(MakeUnique<TxIndexDB>(1 << 20, true));
+    TxIndex txindex(1 << 20, true);
 
     CTransactionRef tx_disk;
     uint256 block_hash;
diff --git a/src/txdb.cpp b/src/txdb.cpp
index 333d3596c1..b1d5879c83 100644
--- a/src/txdb.cpp
+++ b/src/txdb.cpp
@@ -21,8 +21,6 @@
 static const char DB_COIN = 'C';
 static const char DB_COINS = 'c';
 static const char DB_BLOCK_FILES = 'f';
-static const char DB_TXINDEX = 't';
-static const char DB_TXINDEX_BLOCK = 'T';
 static const char DB_BLOCK_INDEX = 'b';
 
 static const char DB_BEST_BLOCK = 'B';
@@ -237,17 +235,6 @@ bool CBlockTreeDB::WriteBatchSync(const std::vector<std::pair<int, const CBlockF
     return WriteBatch(batch, true);
 }
 
-bool CBlockTreeDB::ReadTxIndex(const uint256 &txid, CDiskTxPos &pos) {
-    return Read(std::make_pair(DB_TXINDEX, txid), pos);
-}
-
-bool CBlockTreeDB::WriteTxIndex(const std::vector<std::pair<uint256, CDiskTxPos> >&vect) {
-    CDBBatch batch(*this);
-    for (std::vector<std::pair<uint256,CDiskTxPos> >::const_iterator it=vect.begin(); it!=vect.end(); it++)
-        batch.Write(std::make_pair(DB_TXINDEX, it->first), it->second);
-    return WriteBatch(batch);
-}
-
 bool CBlockTreeDB::WriteFlag(const std::string &name, bool fValue) {
     return Write(std::make_pair(DB_FLAG, name), fValue ? '1' : '0');
 }
@@ -425,173 +412,3 @@ bool CCoinsViewDB::Upgrade() {
     LogPrintf("[%s].\n", ShutdownRequested() ? "CANCELLED" : "DONE");
     return !ShutdownRequested();
 }
-
-TxIndexDB::TxIndexDB(size_t n_cache_size, bool f_memory, bool f_wipe) :
-    CDBWrapper(GetDataDir() / "indexes" / "txindex", n_cache_size, f_memory, f_wipe)
-{}
-
-bool TxIndexDB::ReadTxPos(const uint256 &txid, CDiskTxPos& pos) const
-{
-    return Read(std::make_pair(DB_TXINDEX, txid), pos);
-}
-
-bool TxIndexDB::WriteTxs(const std::vector<std::pair<uint256, CDiskTxPos>>& v_pos)
-{
-    CDBBatch batch(*this);
-    for (const auto& tuple : v_pos) {
-        batch.Write(std::make_pair(DB_TXINDEX, tuple.first), tuple.second);
-    }
-    return WriteBatch(batch);
-}
-
-bool TxIndexDB::ReadBestBlock(CBlockLocator& locator) const
-{
-    bool success = Read(DB_BEST_BLOCK, locator);
-    if (!success) {
-        locator.SetNull();
-    }
-    return success;
-}
-
-bool TxIndexDB::WriteBestBlock(const CBlockLocator& locator)
-{
-    return Write(DB_BEST_BLOCK, locator);
-}
-
-/*
- * Safely persist a transfer of data from the old txindex database to the new one, and compact the
- * range of keys updated. This is used internally by MigrateData.
- */
-static void WriteTxIndexMigrationBatches(TxIndexDB& newdb, CBlockTreeDB& olddb,
-                                         CDBBatch& batch_newdb, CDBBatch& batch_olddb,
-                                         const std::pair<unsigned char, uint256>& begin_key,
-                                         const std::pair<unsigned char, uint256>& end_key)
-{
-    // Sync new DB changes to disk before deleting from old DB.
-    newdb.WriteBatch(batch_newdb, /*fSync=*/ true);
-    olddb.WriteBatch(batch_olddb);
-    olddb.CompactRange(begin_key, end_key);
-
-    batch_newdb.Clear();
-    batch_olddb.Clear();
-}
-
-bool TxIndexDB::MigrateData(CBlockTreeDB& block_tree_db, const CBlockLocator& best_locator)
-{
-    // The prior implementation of txindex was always in sync with block index
-    // and presence was indicated with a boolean DB flag. If the flag is set,
-    // this means the txindex from a previous version is valid and in sync with
-    // the chain tip. The first step of the migration is to unset the flag and
-    // write the chain hash to a separate key, DB_TXINDEX_BLOCK. After that, the
-    // index entries are copied over in batches to the new database. Finally,
-    // DB_TXINDEX_BLOCK is erased from the old database and the block hash is
-    // written to the new database.
-    //
-    // Unsetting the boolean flag ensures that if the node is downgraded to a
-    // previous version, it will not see a corrupted, partially migrated index
-    // -- it will see that the txindex is disabled. When the node is upgraded
-    // again, the migration will pick up where it left off and sync to the block
-    // with hash DB_TXINDEX_BLOCK.
-    bool f_legacy_flag = false;
-    block_tree_db.ReadFlag("txindex", f_legacy_flag);
-    if (f_legacy_flag) {
-        if (!block_tree_db.Write(DB_TXINDEX_BLOCK, best_locator)) {
-            return error("%s: cannot write block indicator", __func__);
-        }
-        if (!block_tree_db.WriteFlag("txindex", false)) {
-            return error("%s: cannot write block index db flag", __func__);
-        }
-    }
-
-    CBlockLocator locator;
-    if (!block_tree_db.Read(DB_TXINDEX_BLOCK, locator)) {
-        return true;
-    }
-
-    int64_t count = 0;
-    LogPrintf("Upgrading txindex database... [0%%]\n");
-    uiInterface.ShowProgress(_("Upgrading txindex database"), 0, true);
-    int report_done = 0;
-    const size_t batch_size = 1 << 24; // 16 MiB
-
-    CDBBatch batch_newdb(*this);
-    CDBBatch batch_olddb(block_tree_db);
-
-    std::pair<unsigned char, uint256> key;
-    std::pair<unsigned char, uint256> begin_key{DB_TXINDEX, uint256()};
-    std::pair<unsigned char, uint256> prev_key = begin_key;
-
-    bool interrupted = false;
-    std::unique_ptr<CDBIterator> cursor(block_tree_db.NewIterator());
-    for (cursor->Seek(begin_key); cursor->Valid(); cursor->Next()) {
-        boost::this_thread::interruption_point();
-        if (ShutdownRequested()) {
-            interrupted = true;
-            break;
-        }
-
-        if (!cursor->GetKey(key)) {
-            return error("%s: cannot get key from valid cursor", __func__);
-        }
-        if (key.first != DB_TXINDEX) {
-            break;
-        }
-
-        // Log progress every 10%.
-        if (++count % 256 == 0) {
-            // Since txids are uniformly random and traversed in increasing order, the high 16 bits
-            // of the hash can be used to estimate the current progress.
-            const uint256& txid = key.second;
-            uint32_t high_nibble =
-                (static_cast<uint32_t>(*(txid.begin() + 0)) << 8) +
-                (static_cast<uint32_t>(*(txid.begin() + 1)) << 0);
-            int percentage_done = (int)(high_nibble * 100.0 / 65536.0 + 0.5);
-
-            uiInterface.ShowProgress(_("Upgrading txindex database"), percentage_done, true);
-            if (report_done < percentage_done/10) {
-                LogPrintf("Upgrading txindex database... [%d%%]\n", percentage_done);
-                report_done = percentage_done/10;
-            }
-        }
-
-        CDiskTxPos value;
-        if (!cursor->GetValue(value)) {
-            return error("%s: cannot parse txindex record", __func__);
-        }
-        batch_newdb.Write(key, value);
-        batch_olddb.Erase(key);
-
-        if (batch_newdb.SizeEstimate() > batch_size || batch_olddb.SizeEstimate() > batch_size) {
-            // NOTE: it's OK to delete the key pointed at by the current DB cursor while iterating
-            // because LevelDB iterators are guaranteed to provide a consistent view of the
-            // underlying data, like a lightweight snapshot.
-            WriteTxIndexMigrationBatches(*this, block_tree_db,
-                                         batch_newdb, batch_olddb,
-                                         prev_key, key);
-            prev_key = key;
-        }
-    }
-
-    // If these final DB batches complete the migration, write the best block
-    // hash marker to the new database and delete from the old one. This signals
-    // that the former is fully caught up to that point in the blockchain and
-    // that all txindex entries have been removed from the latter.
-    if (!interrupted) {
-        batch_olddb.Erase(DB_TXINDEX_BLOCK);
-        batch_newdb.Write(DB_BEST_BLOCK, locator);
-    }
-
-    WriteTxIndexMigrationBatches(*this, block_tree_db,
-                                 batch_newdb, batch_olddb,
-                                 begin_key, key);
-
-    if (interrupted) {
-        LogPrintf("[CANCELLED].\n");
-        return false;
-    }
-
-    uiInterface.ShowProgress("", 100, false);
-
-    LogPrintf("[DONE].\n");
-    return true;
-}
diff --git a/src/txdb.h b/src/txdb.h
index 4193f98de1..100adb428d 100644
--- a/src/txdb.h
+++ b/src/txdb.h
@@ -40,31 +40,6 @@ static const int64_t nMaxTxIndexCache = 1024;
 //! Max memory allocated to coin DB specific cache (MiB)
 static const int64_t nMaxCoinsDBCache = 8;
 
-struct CDiskTxPos : public CDiskBlockPos
-{
-    unsigned int nTxOffset; // after header
-
-    ADD_SERIALIZE_METHODS;
-
-    template <typename Stream, typename Operation>
-    inline void SerializationOp(Stream& s, Operation ser_action) {
-        READWRITEAS(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;
-    }
-};
-
 /** CCoinsView backed by the coin database (chainstate/) */
 class CCoinsViewDB final : public CCoinsView
 {
@@ -118,43 +93,9 @@ public:
     bool ReadLastBlockFile(int &nFile);
     bool WriteReindexing(bool fReindexing);
     bool ReadReindexing(bool &fReindexing);
-    bool ReadTxIndex(const uint256 &txid, CDiskTxPos &pos);
-    bool WriteTxIndex(const std::vector<std::pair<uint256, CDiskTxPos> > &vect);
     bool WriteFlag(const std::string &name, bool fValue);
     bool ReadFlag(const std::string &name, bool &fValue);
     bool LoadBlockIndexGuts(const Consensus::Params& consensusParams, std::function<CBlockIndex*(const uint256&)> insertBlockIndex);
 };
 
-/**
- * Access to the txindex database (indexes/txindex/)
- *
- * The database stores a block locator of the chain the database is synced to
- * so that the TxIndex can efficiently determine the point it last stopped at.
- * A locator is used instead of a simple hash of the chain tip because blocks
- * and block index entries may not be flushed to disk until after this database
- * is updated.
- */
-class TxIndexDB : public CDBWrapper
-{
-public:
-    explicit TxIndexDB(size_t n_cache_size, bool f_memory = false, bool f_wipe = false);
-
-    /// Read the disk location of the transaction data with the given hash. Returns false if the
-    /// transaction hash is not indexed.
-    bool ReadTxPos(const uint256& txid, CDiskTxPos& pos) const;
-
-    /// Write a batch of transaction positions to the DB.
-    bool WriteTxs(const std::vector<std::pair<uint256, CDiskTxPos>>& v_pos);
-
-    /// Read block locator of the chain that the txindex is in sync with.
-    bool ReadBestBlock(CBlockLocator& locator) const;
-
-    /// Write block locator of the chain that the txindex is in sync with.
-    bool WriteBestBlock(const CBlockLocator& locator);
-
-    /// Migrate txindex data from the block tree DB, where it may be for older nodes that have not
-    /// been upgraded yet to the new database.
-    bool MigrateData(CBlockTreeDB& block_tree_db, const CBlockLocator& best_locator);
-};
-
 #endif // BITCOIN_TXDB_H