Merge #19290: wallet: move BDB specific classes to bdb.{cpp/h}

61c16339da4e80b1320a6296df6d96cd7a84bb4e walletdb: Move BDB specific things into bdb.{cpp/h} (Andrew Chow)
8f033642a8c6874184e297b97b951b9bd12ffd75 walletdb: moveonly: Move BerkeleyBatch Cursor and Txn funcs to cpp (Andrew Chow)
25a655794a0c495332dadedd88b87d694c1077c2 walletdb: move IsWalletLoaded to walletdb.cpp (Andrew Chow)
f6fc5f3849bac48dfccd015bec7089cb711d0667 walletdb: Add IsBDBWalletLoaded to look for BDB wallets specifically (Andrew Chow)
c3538f435af8c408759d9d005e80b2f1690e0659 walletdb: Make SpliWalletFilePath non-static (Andrew Chow)

Pull request description:

  Moves the BDB specific classes from db.{cpp/h} to bdb.{cpp/h}.

  To do this, `SplitWalletFilePath` is first made non-static. Then `IsWalletLoaded` functionality is moved to `IsBDBWalletLoaded` which is called by `IsWalletLoaded`. Then the bulk of db.{cpp/h} is moved to a new file bdb.{cpp/h}.

  While doing some moveonly stuff, an additional commit moves the `*Cursor` and `Txn*` implementations out of the header file and into the cpp file.

  Part of #18971

ACKs for top commit:
  laanwj:
    Code review ACK 61c16339da4e80b1320a6296df6d96cd7a84bb4e
  promag:
    Code review ACK 61c16339da4e80b1320a6296df6d96cd7a84bb4e.
  meshcollider:
    utACK 61c16339da4e80b1320a6296df6d96cd7a84bb4e

Tree-SHA512: cb676cd34c9cd3c838a4fef230d84711efe4cf0d2eefa64ebfd7f787ddc6f7379db0b29454874ddc46ca7ffee0f18f6f3fb96a85513cd10164048948fd03a80c

9 files changed, 1159 insertions, 1116 deletions

diff --git a/src/Makefile.am b/src/Makefile.am
index 7a280a67a7..a33ff8a461 100644
--- a/src/Makefile.am
+++ b/src/Makefile.am
@@ -240,6 +240,7 @@ BITCOIN_CORE_H = \
   versionbits.h \
   versionbitsinfo.h \
   walletinitinterface.h \
+  wallet/bdb.h \
   wallet/coincontrol.h \
   wallet/context.h \
   wallet/crypter.h \
@@ -350,6 +351,7 @@ libbitcoin_wallet_a_CPPFLAGS = $(AM_CPPFLAGS) $(BITCOIN_INCLUDES)
 libbitcoin_wallet_a_CXXFLAGS = $(AM_CXXFLAGS) $(PIE_FLAGS)
 libbitcoin_wallet_a_SOURCES = \
   interfaces/wallet.cpp \
+  wallet/bdb.cpp \
   wallet/coincontrol.cpp \
   wallet/context.cpp \
   wallet/crypter.cpp \
diff --git a/src/qt/rpcconsole.cpp b/src/qt/rpcconsole.cpp
index 0f89d4e6fe..dafd517ca8 100644
--- a/src/qt/rpcconsole.cpp
+++ b/src/qt/rpcconsole.cpp
@@ -24,6 +24,7 @@
 #include <univalue.h>
 
 #ifdef ENABLE_WALLET
+#include <wallet/bdb.h>
 #include <wallet/db.h>
 #include <wallet/wallet.h>
 #endif
diff --git a/src/wallet/bdb.cpp b/src/wallet/bdb.cpp
new file mode 100644
index 0000000000..7ed9c88122
--- /dev/null
+++ b/src/wallet/bdb.cpp
@@ -0,0 +1,805 @@
+// Copyright (c) 2009-2010 Satoshi Nakamoto
+// Copyright (c) 2009-2020 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 <wallet/bdb.h>
+#include <wallet/db.h>
+
+#include <util/strencodings.h>
+#include <util/translation.h>
+
+#include <stdint.h>
+
+#ifndef WIN32
+#include <sys/stat.h>
+#endif
+
+namespace {
+
+//! Make sure database has a unique fileid within the environment. If it
+//! doesn't, throw an error. BDB caches do not work properly when more than one
+//! open database has the same fileid (values written to one database may show
+//! up in reads to other databases).
+//!
+//! BerkeleyDB generates unique fileids by default
+//! (https://docs.oracle.com/cd/E17275_01/html/programmer_reference/program_copy.html),
+//! so bitcoin should never create different databases with the same fileid, but
+//! this error can be triggered if users manually copy database files.
+void CheckUniqueFileid(const BerkeleyEnvironment& env, const std::string& filename, Db& db, WalletDatabaseFileId& fileid)
+{
+    if (env.IsMock()) return;
+
+    int ret = db.get_mpf()->get_fileid(fileid.value);
+    if (ret != 0) {
+        throw std::runtime_error(strprintf("BerkeleyBatch: Can't open database %s (get_fileid failed with %d)", filename, ret));
+    }
+
+    for (const auto& item : env.m_fileids) {
+        if (fileid == item.second && &fileid != &item.second) {
+            throw std::runtime_error(strprintf("BerkeleyBatch: Can't open database %s (duplicates fileid %s from %s)", filename,
+                HexStr(std::begin(item.second.value), std::end(item.second.value)), item.first));
+        }
+    }
+}
+
+RecursiveMutex cs_db;
+std::map<std::string, std::weak_ptr<BerkeleyEnvironment>> g_dbenvs GUARDED_BY(cs_db); //!< Map from directory name to db environment.
+} // namespace
+
+bool WalletDatabaseFileId::operator==(const WalletDatabaseFileId& rhs) const
+{
+    return memcmp(value, &rhs.value, sizeof(value)) == 0;
+}
+
+bool IsBDBWalletLoaded(const fs::path& wallet_path)
+{
+    fs::path env_directory;
+    std::string database_filename;
+    SplitWalletPath(wallet_path, env_directory, database_filename);
+    LOCK(cs_db);
+    auto env = g_dbenvs.find(env_directory.string());
+    if (env == g_dbenvs.end()) return false;
+    auto database = env->second.lock();
+    return database && database->IsDatabaseLoaded(database_filename);
+}
+
+/**
+ * @param[in] wallet_path Path to wallet directory. Or (for backwards compatibility only) a path to a berkeley btree data file inside a wallet directory.
+ * @param[out] database_filename Filename of berkeley btree data file inside the wallet directory.
+ * @return A shared pointer to the BerkeleyEnvironment object for the wallet directory, never empty because ~BerkeleyEnvironment
+ * erases the weak pointer from the g_dbenvs map.
+ * @post A new BerkeleyEnvironment weak pointer is inserted into g_dbenvs if the directory path key was not already in the map.
+ */
+std::shared_ptr<BerkeleyEnvironment> GetWalletEnv(const fs::path& wallet_path, std::string& database_filename)
+{
+    fs::path env_directory;
+    SplitWalletPath(wallet_path, env_directory, database_filename);
+    LOCK(cs_db);
+    auto inserted = g_dbenvs.emplace(env_directory.string(), std::weak_ptr<BerkeleyEnvironment>());
+    if (inserted.second) {
+        auto env = std::make_shared<BerkeleyEnvironment>(env_directory.string());
+        inserted.first->second = env;
+        return env;
+    }
+    return inserted.first->second.lock();
+}
+
+//
+// BerkeleyBatch
+//
+
+void BerkeleyEnvironment::Close()
+{
+    if (!fDbEnvInit)
+        return;
+
+    fDbEnvInit = false;
+
+    for (auto& db : m_databases) {
+        auto count = mapFileUseCount.find(db.first);
+        assert(count == mapFileUseCount.end() || count->second == 0);
+        BerkeleyDatabase& database = db.second.get();
+        if (database.m_db) {
+            database.m_db->close(0);
+            database.m_db.reset();
+        }
+    }
+
+    FILE* error_file = nullptr;
+    dbenv->get_errfile(&error_file);
+
+    int ret = dbenv->close(0);
+    if (ret != 0)
+        LogPrintf("BerkeleyEnvironment::Close: Error %d closing database environment: %s\n", ret, DbEnv::strerror(ret));
+    if (!fMockDb)
+        DbEnv((u_int32_t)0).remove(strPath.c_str(), 0);
+
+    if (error_file) fclose(error_file);
+
+    UnlockDirectory(strPath, ".walletlock");
+}
+
+void BerkeleyEnvironment::Reset()
+{
+    dbenv.reset(new DbEnv(DB_CXX_NO_EXCEPTIONS));
+    fDbEnvInit = false;
+    fMockDb = false;
+}
+
+BerkeleyEnvironment::BerkeleyEnvironment(const fs::path& dir_path) : strPath(dir_path.string())
+{
+    Reset();
+}
+
+BerkeleyEnvironment::~BerkeleyEnvironment()
+{
+    LOCK(cs_db);
+    g_dbenvs.erase(strPath);
+    Close();
+}
+
+bool BerkeleyEnvironment::Open(bool retry)
+{
+    if (fDbEnvInit) {
+        return true;
+    }
+
+    fs::path pathIn = strPath;
+    TryCreateDirectories(pathIn);
+    if (!LockDirectory(pathIn, ".walletlock")) {
+        LogPrintf("Cannot obtain a lock on wallet directory %s. Another instance of bitcoin may be using it.\n", strPath);
+        return false;
+    }
+
+    fs::path pathLogDir = pathIn / "database";
+    TryCreateDirectories(pathLogDir);
+    fs::path pathErrorFile = pathIn / "db.log";
+    LogPrintf("BerkeleyEnvironment::Open: LogDir=%s ErrorFile=%s\n", pathLogDir.string(), pathErrorFile.string());
+
+    unsigned int nEnvFlags = 0;
+    if (gArgs.GetBoolArg("-privdb", DEFAULT_WALLET_PRIVDB))
+        nEnvFlags |= DB_PRIVATE;
+
+    dbenv->set_lg_dir(pathLogDir.string().c_str());
+    dbenv->set_cachesize(0, 0x100000, 1); // 1 MiB should be enough for just the wallet
+    dbenv->set_lg_bsize(0x10000);
+    dbenv->set_lg_max(1048576);
+    dbenv->set_lk_max_locks(40000);
+    dbenv->set_lk_max_objects(40000);
+    dbenv->set_errfile(fsbridge::fopen(pathErrorFile, "a")); /// debug
+    dbenv->set_flags(DB_AUTO_COMMIT, 1);
+    dbenv->set_flags(DB_TXN_WRITE_NOSYNC, 1);
+    dbenv->log_set_config(DB_LOG_AUTO_REMOVE, 1);
+    int ret = dbenv->open(strPath.c_str(),
+                         DB_CREATE |
+                             DB_INIT_LOCK |
+                             DB_INIT_LOG |
+                             DB_INIT_MPOOL |
+                             DB_INIT_TXN |
+                             DB_THREAD |
+                             DB_RECOVER |
+                             nEnvFlags,
+                         S_IRUSR | S_IWUSR);
+    if (ret != 0) {
+        LogPrintf("BerkeleyEnvironment::Open: Error %d opening database environment: %s\n", ret, DbEnv::strerror(ret));
+        int ret2 = dbenv->close(0);
+        if (ret2 != 0) {
+            LogPrintf("BerkeleyEnvironment::Open: Error %d closing failed database environment: %s\n", ret2, DbEnv::strerror(ret2));
+        }
+        Reset();
+        if (retry) {
+            // try moving the database env out of the way
+            fs::path pathDatabaseBak = pathIn / strprintf("database.%d.bak", GetTime());
+            try {
+                fs::rename(pathLogDir, pathDatabaseBak);
+                LogPrintf("Moved old %s to %s. Retrying.\n", pathLogDir.string(), pathDatabaseBak.string());
+            } catch (const fs::filesystem_error&) {
+                // failure is ok (well, not really, but it's not worse than what we started with)
+            }
+            // try opening it again one more time
+            if (!Open(false /* retry */)) {
+                // if it still fails, it probably means we can't even create the database env
+                return false;
+            }
+        } else {
+            return false;
+        }
+    }
+
+    fDbEnvInit = true;
+    fMockDb = false;
+    return true;
+}
+
+//! Construct an in-memory mock Berkeley environment for testing
+BerkeleyEnvironment::BerkeleyEnvironment()
+{
+    Reset();
+
+    LogPrint(BCLog::WALLETDB, "BerkeleyEnvironment::MakeMock\n");
+
+    dbenv->set_cachesize(1, 0, 1);
+    dbenv->set_lg_bsize(10485760 * 4);
+    dbenv->set_lg_max(10485760);
+    dbenv->set_lk_max_locks(10000);
+    dbenv->set_lk_max_objects(10000);
+    dbenv->set_flags(DB_AUTO_COMMIT, 1);
+    dbenv->log_set_config(DB_LOG_IN_MEMORY, 1);
+    int ret = dbenv->open(nullptr,
+                         DB_CREATE |
+                             DB_INIT_LOCK |
+                             DB_INIT_LOG |
+                             DB_INIT_MPOOL |
+                             DB_INIT_TXN |
+                             DB_THREAD |
+                             DB_PRIVATE,
+                         S_IRUSR | S_IWUSR);
+    if (ret > 0) {
+        throw std::runtime_error(strprintf("BerkeleyEnvironment::MakeMock: Error %d opening database environment.", ret));
+    }
+
+    fDbEnvInit = true;
+    fMockDb = true;
+}
+
+bool BerkeleyEnvironment::Verify(const std::string& strFile)
+{
+    LOCK(cs_db);
+    assert(mapFileUseCount.count(strFile) == 0);
+
+    Db db(dbenv.get(), 0);
+    int result = db.verify(strFile.c_str(), nullptr, nullptr, 0);
+    return result == 0;
+}
+
+BerkeleyBatch::SafeDbt::SafeDbt()
+{
+    m_dbt.set_flags(DB_DBT_MALLOC);
+}
+
+BerkeleyBatch::SafeDbt::SafeDbt(void* data, size_t size)
+    : m_dbt(data, size)
+{
+}
+
+BerkeleyBatch::SafeDbt::~SafeDbt()
+{
+    if (m_dbt.get_data() != nullptr) {
+        // Clear memory, e.g. in case it was a private key
+        memory_cleanse(m_dbt.get_data(), m_dbt.get_size());
+        // under DB_DBT_MALLOC, data is malloced by the Dbt, but must be
+        // freed by the caller.
+        // https://docs.oracle.com/cd/E17275_01/html/api_reference/C/dbt.html
+        if (m_dbt.get_flags() & DB_DBT_MALLOC) {
+            free(m_dbt.get_data());
+        }
+    }
+}
+
+const void* BerkeleyBatch::SafeDbt::get_data() const
+{
+    return m_dbt.get_data();
+}
+
+u_int32_t BerkeleyBatch::SafeDbt::get_size() const
+{
+    return m_dbt.get_size();
+}
+
+BerkeleyBatch::SafeDbt::operator Dbt*()
+{
+    return &m_dbt;
+}
+
+bool BerkeleyBatch::VerifyEnvironment(const fs::path& file_path, bilingual_str& errorStr)
+{
+    std::string walletFile;
+    std::shared_ptr<BerkeleyEnvironment> env = GetWalletEnv(file_path, walletFile);
+    fs::path walletDir = env->Directory();
+
+    LogPrintf("Using BerkeleyDB version %s\n", BerkeleyDatabaseVersion());
+    LogPrintf("Using wallet %s\n", file_path.string());
+
+    if (!env->Open(true /* retry */)) {
+        errorStr = strprintf(_("Error initializing wallet database environment %s!"), walletDir);
+        return false;
+    }
+
+    return true;
+}
+
+bool BerkeleyBatch::VerifyDatabaseFile(const fs::path& file_path, bilingual_str& errorStr)
+{
+    std::string walletFile;
+    std::shared_ptr<BerkeleyEnvironment> env = GetWalletEnv(file_path, walletFile);
+    fs::path walletDir = env->Directory();
+
+    if (fs::exists(walletDir / walletFile))
+    {
+        if (!env->Verify(walletFile)) {
+            errorStr = strprintf(_("%s corrupt. Try using the wallet tool bitcoin-wallet to salvage or restoring a backup."), walletFile);
+            return false;
+        }
+    }
+    // also return true if files does not exists
+    return true;
+}
+
+void BerkeleyEnvironment::CheckpointLSN(const std::string& strFile)
+{
+    dbenv->txn_checkpoint(0, 0, 0);
+    if (fMockDb)
+        return;
+    dbenv->lsn_reset(strFile.c_str(), 0);
+}
+
+
+BerkeleyBatch::BerkeleyBatch(BerkeleyDatabase& database, const char* pszMode, bool fFlushOnCloseIn) : pdb(nullptr), activeTxn(nullptr)
+{
+    fReadOnly = (!strchr(pszMode, '+') && !strchr(pszMode, 'w'));
+    fFlushOnClose = fFlushOnCloseIn;
+    env = database.env.get();
+    if (database.IsDummy()) {
+        return;
+    }
+    const std::string &strFilename = database.strFile;
+
+    bool fCreate = strchr(pszMode, 'c') != nullptr;
+    unsigned int nFlags = DB_THREAD;
+    if (fCreate)
+        nFlags |= DB_CREATE;
+
+    {
+        LOCK(cs_db);
+        if (!env->Open(false /* retry */))
+            throw std::runtime_error("BerkeleyBatch: Failed to open database environment.");
+
+        pdb = database.m_db.get();
+        if (pdb == nullptr) {
+            int ret;
+            std::unique_ptr<Db> pdb_temp = MakeUnique<Db>(env->dbenv.get(), 0);
+
+            bool fMockDb = env->IsMock();
+            if (fMockDb) {
+                DbMpoolFile* mpf = pdb_temp->get_mpf();
+                ret = mpf->set_flags(DB_MPOOL_NOFILE, 1);
+                if (ret != 0) {
+                    throw std::runtime_error(strprintf("BerkeleyBatch: Failed to configure for no temp file backing for database %s", strFilename));
+                }
+            }
+
+            ret = pdb_temp->open(nullptr,                             // Txn pointer
+                            fMockDb ? nullptr : strFilename.c_str(),  // Filename
+                            fMockDb ? strFilename.c_str() : "main",   // Logical db name
+                            DB_BTREE,                                 // Database type
+                            nFlags,                                   // Flags
+                            0);
+
+            if (ret != 0) {
+                throw std::runtime_error(strprintf("BerkeleyBatch: Error %d, can't open database %s", ret, strFilename));
+            }
+
+            // Call CheckUniqueFileid on the containing BDB environment to
+            // avoid BDB data consistency bugs that happen when different data
+            // files in the same environment have the same fileid.
+            //
+            // Also call CheckUniqueFileid on all the other g_dbenvs to prevent
+            // bitcoin from opening the same data file through another
+            // environment when the file is referenced through equivalent but
+            // not obviously identical symlinked or hard linked or bind mounted
+            // paths. In the future a more relaxed check for equal inode and
+            // device ids could be done instead, which would allow opening
+            // different backup copies of a wallet at the same time. Maybe even
+            // more ideally, an exclusive lock for accessing the database could
+            // be implemented, so no equality checks are needed at all. (Newer
+            // versions of BDB have an set_lk_exclusive method for this
+            // purpose, but the older version we use does not.)
+            for (const auto& env : g_dbenvs) {
+                CheckUniqueFileid(*env.second.lock().get(), strFilename, *pdb_temp, this->env->m_fileids[strFilename]);
+            }
+
+            pdb = pdb_temp.release();
+            database.m_db.reset(pdb);
+
+            if (fCreate && !Exists(std::string("version"))) {
+                bool fTmp = fReadOnly;
+                fReadOnly = false;
+                Write(std::string("version"), CLIENT_VERSION);
+                fReadOnly = fTmp;
+            }
+        }
+        ++env->mapFileUseCount[strFilename];
+        strFile = strFilename;
+    }
+}
+
+void BerkeleyBatch::Flush()
+{
+    if (activeTxn)
+        return;
+
+    // Flush database activity from memory pool to disk log
+    unsigned int nMinutes = 0;
+    if (fReadOnly)
+        nMinutes = 1;
+
+    if (env) { // env is nullptr for dummy databases (i.e. in tests). Don't actually flush if env is nullptr so we don't segfault
+        env->dbenv->txn_checkpoint(nMinutes ? gArgs.GetArg("-dblogsize", DEFAULT_WALLET_DBLOGSIZE) * 1024 : 0, nMinutes, 0);
+    }
+}
+
+void BerkeleyDatabase::IncrementUpdateCounter()
+{
+    ++nUpdateCounter;
+}
+
+void BerkeleyBatch::Close()
+{
+    if (!pdb)
+        return;
+    if (activeTxn)
+        activeTxn->abort();
+    activeTxn = nullptr;
+    pdb = nullptr;
+
+    if (fFlushOnClose)
+        Flush();
+
+    {
+        LOCK(cs_db);
+        --env->mapFileUseCount[strFile];
+    }
+    env->m_db_in_use.notify_all();
+}
+
+void BerkeleyEnvironment::CloseDb(const std::string& strFile)
+{
+    {
+        LOCK(cs_db);
+        auto it = m_databases.find(strFile);
+        assert(it != m_databases.end());
+        BerkeleyDatabase& database = it->second.get();
+        if (database.m_db) {
+            // Close the database handle
+            database.m_db->close(0);
+            database.m_db.reset();
+        }
+    }
+}
+
+void BerkeleyEnvironment::ReloadDbEnv()
+{
+    // Make sure that no Db's are in use
+    AssertLockNotHeld(cs_db);
+    std::unique_lock<RecursiveMutex> lock(cs_db);
+    m_db_in_use.wait(lock, [this](){
+        for (auto& count : mapFileUseCount) {
+            if (count.second > 0) return false;
+        }
+        return true;
+    });
+
+    std::vector<std::string> filenames;
+    for (auto it : m_databases) {
+        filenames.push_back(it.first);
+    }
+    // Close the individual Db's
+    for (const std::string& filename : filenames) {
+        CloseDb(filename);
+    }
+    // Reset the environment
+    Flush(true); // This will flush and close the environment
+    Reset();
+    Open(true);
+}
+
+bool BerkeleyBatch::Rewrite(BerkeleyDatabase& database, const char* pszSkip)
+{
+    if (database.IsDummy()) {
+        return true;
+    }
+    BerkeleyEnvironment *env = database.env.get();
+    const std::string& strFile = database.strFile;
+    while (true) {
+        {
+            LOCK(cs_db);
+            if (!env->mapFileUseCount.count(strFile) || env->mapFileUseCount[strFile] == 0) {
+                // Flush log data to the dat file
+                env->CloseDb(strFile);
+                env->CheckpointLSN(strFile);
+                env->mapFileUseCount.erase(strFile);
+
+                bool fSuccess = true;
+                LogPrintf("BerkeleyBatch::Rewrite: Rewriting %s...\n", strFile);
+                std::string strFileRes = strFile + ".rewrite";
+                { // surround usage of db with extra {}
+                    BerkeleyBatch db(database, "r");
+                    std::unique_ptr<Db> pdbCopy = MakeUnique<Db>(env->dbenv.get(), 0);
+
+                    int ret = pdbCopy->open(nullptr,               // Txn pointer
+                                            strFileRes.c_str(), // Filename
+                                            "main",             // Logical db name
+                                            DB_BTREE,           // Database type
+                                            DB_CREATE,          // Flags
+                                            0);
+                    if (ret > 0) {
+                        LogPrintf("BerkeleyBatch::Rewrite: Can't create database file %s\n", strFileRes);
+                        fSuccess = false;
+                    }
+
+                    Dbc* pcursor = db.GetCursor();
+                    if (pcursor)
+                        while (fSuccess) {
+                            CDataStream ssKey(SER_DISK, CLIENT_VERSION);
+                            CDataStream ssValue(SER_DISK, CLIENT_VERSION);
+                            int ret1 = db.ReadAtCursor(pcursor, ssKey, ssValue);
+                            if (ret1 == DB_NOTFOUND) {
+                                pcursor->close();
+                                break;
+                            } else if (ret1 != 0) {
+                                pcursor->close();
+                                fSuccess = false;
+                                break;
+                            }
+                            if (pszSkip &&
+                                strncmp(ssKey.data(), pszSkip, std::min(ssKey.size(), strlen(pszSkip))) == 0)
+                                continue;
+                            if (strncmp(ssKey.data(), "\x07version", 8) == 0) {
+                                // Update version:
+                                ssValue.clear();
+                                ssValue << CLIENT_VERSION;
+                            }
+                            Dbt datKey(ssKey.data(), ssKey.size());
+                            Dbt datValue(ssValue.data(), ssValue.size());
+                            int ret2 = pdbCopy->put(nullptr, &datKey, &datValue, DB_NOOVERWRITE);
+                            if (ret2 > 0)
+                                fSuccess = false;
+                        }
+                    if (fSuccess) {
+                        db.Close();
+                        env->CloseDb(strFile);
+                        if (pdbCopy->close(0))
+                            fSuccess = false;
+                    } else {
+                        pdbCopy->close(0);
+                    }
+                }
+                if (fSuccess) {
+                    Db dbA(env->dbenv.get(), 0);
+                    if (dbA.remove(strFile.c_str(), nullptr, 0))
+                        fSuccess = false;
+                    Db dbB(env->dbenv.get(), 0);
+                    if (dbB.rename(strFileRes.c_str(), nullptr, strFile.c_str(), 0))
+                        fSuccess = false;
+                }
+                if (!fSuccess)
+                    LogPrintf("BerkeleyBatch::Rewrite: Failed to rewrite database file %s\n", strFileRes);
+                return fSuccess;
+            }
+        }
+        UninterruptibleSleep(std::chrono::milliseconds{100});
+    }
+}
+
+
+void BerkeleyEnvironment::Flush(bool fShutdown)
+{
+    int64_t nStart = GetTimeMillis();
+    // Flush log data to the actual data file on all files that are not in use
+    LogPrint(BCLog::WALLETDB, "BerkeleyEnvironment::Flush: [%s] Flush(%s)%s\n", strPath, fShutdown ? "true" : "false", fDbEnvInit ? "" : " database not started");
+    if (!fDbEnvInit)
+        return;
+    {
+        LOCK(cs_db);
+        std::map<std::string, int>::iterator mi = mapFileUseCount.begin();
+        while (mi != mapFileUseCount.end()) {
+            std::string strFile = (*mi).first;
+            int nRefCount = (*mi).second;
+            LogPrint(BCLog::WALLETDB, "BerkeleyEnvironment::Flush: Flushing %s (refcount = %d)...\n", strFile, nRefCount);
+            if (nRefCount == 0) {
+                // Move log data to the dat file
+                CloseDb(strFile);
+                LogPrint(BCLog::WALLETDB, "BerkeleyEnvironment::Flush: %s checkpoint\n", strFile);
+                dbenv->txn_checkpoint(0, 0, 0);
+                LogPrint(BCLog::WALLETDB, "BerkeleyEnvironment::Flush: %s detach\n", strFile);
+                if (!fMockDb)
+                    dbenv->lsn_reset(strFile.c_str(), 0);
+                LogPrint(BCLog::WALLETDB, "BerkeleyEnvironment::Flush: %s closed\n", strFile);
+                mapFileUseCount.erase(mi++);
+            } else
+                mi++;
+        }
+        LogPrint(BCLog::WALLETDB, "BerkeleyEnvironment::Flush: Flush(%s)%s took %15dms\n", fShutdown ? "true" : "false", fDbEnvInit ? "" : " database not started", GetTimeMillis() - nStart);
+        if (fShutdown) {
+            char** listp;
+            if (mapFileUseCount.empty()) {
+                dbenv->log_archive(&listp, DB_ARCH_REMOVE);
+                Close();
+                if (!fMockDb) {
+                    fs::remove_all(fs::path(strPath) / "database");
+                }
+            }
+        }
+    }
+}
+
+bool BerkeleyBatch::PeriodicFlush(BerkeleyDatabase& database)
+{
+    if (database.IsDummy()) {
+        return true;
+    }
+    bool ret = false;
+    BerkeleyEnvironment *env = database.env.get();
+    const std::string& strFile = database.strFile;
+    TRY_LOCK(cs_db, lockDb);
+    if (lockDb)
+    {
+        // Don't do this if any databases are in use
+        int nRefCount = 0;
+        std::map<std::string, int>::iterator mit = env->mapFileUseCount.begin();
+        while (mit != env->mapFileUseCount.end())
+        {
+            nRefCount += (*mit).second;
+            mit++;
+        }
+
+        if (nRefCount == 0)
+        {
+            std::map<std::string, int>::iterator mi = env->mapFileUseCount.find(strFile);
+            if (mi != env->mapFileUseCount.end())
+            {
+                LogPrint(BCLog::WALLETDB, "Flushing %s\n", strFile);
+                int64_t nStart = GetTimeMillis();
+
+                // Flush wallet file so it's self contained
+                env->CloseDb(strFile);
+                env->CheckpointLSN(strFile);
+
+                env->mapFileUseCount.erase(mi++);
+                LogPrint(BCLog::WALLETDB, "Flushed %s %dms\n", strFile, GetTimeMillis() - nStart);
+                ret = true;
+            }
+        }
+    }
+
+    return ret;
+}
+
+bool BerkeleyDatabase::Rewrite(const char* pszSkip)
+{
+    return BerkeleyBatch::Rewrite(*this, pszSkip);
+}
+
+bool BerkeleyDatabase::Backup(const std::string& strDest) const
+{
+    if (IsDummy()) {
+        return false;
+    }
+    while (true)
+    {
+        {
+            LOCK(cs_db);
+            if (!env->mapFileUseCount.count(strFile) || env->mapFileUseCount[strFile] == 0)
+            {
+                // Flush log data to the dat file
+                env->CloseDb(strFile);
+                env->CheckpointLSN(strFile);
+                env->mapFileUseCount.erase(strFile);
+
+                // Copy wallet file
+                fs::path pathSrc = env->Directory() / strFile;
+                fs::path pathDest(strDest);
+                if (fs::is_directory(pathDest))
+                    pathDest /= strFile;
+
+                try {
+                    if (fs::equivalent(pathSrc, pathDest)) {
+                        LogPrintf("cannot backup to wallet source file %s\n", pathDest.string());
+                        return false;
+                    }
+
+                    fs::copy_file(pathSrc, pathDest, fs::copy_option::overwrite_if_exists);
+                    LogPrintf("copied %s to %s\n", strFile, pathDest.string());
+                    return true;
+                } catch (const fs::filesystem_error& e) {
+                    LogPrintf("error copying %s to %s - %s\n", strFile, pathDest.string(), fsbridge::get_filesystem_error_message(e));
+                    return false;
+                }
+            }
+        }
+        UninterruptibleSleep(std::chrono::milliseconds{100});
+    }
+}
+
+void BerkeleyDatabase::Flush(bool shutdown)
+{
+    if (!IsDummy()) {
+        env->Flush(shutdown);
+        if (shutdown) {
+            LOCK(cs_db);
+            g_dbenvs.erase(env->Directory().string());
+            env = nullptr;
+        } else {
+            // TODO: To avoid g_dbenvs.erase erasing the environment prematurely after the
+            // first database shutdown when multiple databases are open in the same
+            // environment, should replace raw database `env` pointers with shared or weak
+            // pointers, or else separate the database and environment shutdowns so
+            // environments can be shut down after databases.
+            env->m_fileids.erase(strFile);
+        }
+    }
+}
+
+void BerkeleyDatabase::ReloadDbEnv()
+{
+    if (!IsDummy()) {
+        env->ReloadDbEnv();
+    }
+}
+
+Dbc* BerkeleyBatch::GetCursor()
+{
+    if (!pdb)
+        return nullptr;
+    Dbc* pcursor = nullptr;
+    int ret = pdb->cursor(nullptr, &pcursor, 0);
+    if (ret != 0)
+        return nullptr;
+    return pcursor;
+}
+
+int BerkeleyBatch::ReadAtCursor(Dbc* pcursor, CDataStream& ssKey, CDataStream& ssValue)
+{
+    // Read at cursor
+    SafeDbt datKey;
+    SafeDbt datValue;
+    int ret = pcursor->get(datKey, datValue, DB_NEXT);
+    if (ret != 0)
+        return ret;
+    else if (datKey.get_data() == nullptr || datValue.get_data() == nullptr)
+        return 99999;
+
+    // Convert to streams
+    ssKey.SetType(SER_DISK);
+    ssKey.clear();
+    ssKey.write((char*)datKey.get_data(), datKey.get_size());
+    ssValue.SetType(SER_DISK);
+    ssValue.clear();
+    ssValue.write((char*)datValue.get_data(), datValue.get_size());
+    return 0;
+}
+
+bool BerkeleyBatch::TxnBegin()
+{
+    if (!pdb || activeTxn)
+        return false;
+    DbTxn* ptxn = env->TxnBegin();
+    if (!ptxn)
+        return false;
+    activeTxn = ptxn;
+    return true;
+}
+
+bool BerkeleyBatch::TxnCommit()
+{
+    if (!pdb || !activeTxn)
+        return false;
+    int ret = activeTxn->commit(0);
+    activeTxn = nullptr;
+    return (ret == 0);
+}
+
+bool BerkeleyBatch::TxnAbort()
+{
+    if (!pdb || !activeTxn)
+        return false;
+    int ret = activeTxn->abort();
+    activeTxn = nullptr;
+    return (ret == 0);
+}
+
+std::string BerkeleyDatabaseVersion()
+{
+    return DbEnv::version(nullptr, nullptr, nullptr);
+}
diff --git a/src/wallet/bdb.h b/src/wallet/bdb.h
new file mode 100644
index 0000000000..5ed364344b
--- /dev/null
+++ b/src/wallet/bdb.h
@@ -0,0 +1,337 @@
+// Copyright (c) 2009-2010 Satoshi Nakamoto
+// Copyright (c) 2009-2020 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_WALLET_BDB_H
+#define BITCOIN_WALLET_BDB_H
+
+#include <clientversion.h>
+#include <fs.h>
+#include <serialize.h>
+#include <streams.h>
+#include <util/system.h>
+#include <wallet/db.h>
+
+#include <atomic>
+#include <map>
+#include <memory>
+#include <string>
+#include <unordered_map>
+#include <vector>
+
+#if defined(__GNUC__) && !defined(__clang__)
+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Wsuggest-override"
+#endif
+#include <db_cxx.h>
+#if defined(__GNUC__) && !defined(__clang__)
+#pragma GCC diagnostic pop
+#endif
+
+struct bilingual_str;
+
+static const unsigned int DEFAULT_WALLET_DBLOGSIZE = 100;
+static const bool DEFAULT_WALLET_PRIVDB = true;
+
+struct WalletDatabaseFileId {
+    u_int8_t value[DB_FILE_ID_LEN];
+    bool operator==(const WalletDatabaseFileId& rhs) const;
+};
+
+class BerkeleyDatabase;
+
+class BerkeleyEnvironment
+{
+private:
+    bool fDbEnvInit;
+    bool fMockDb;
+    // Don't change into fs::path, as that can result in
+    // shutdown problems/crashes caused by a static initialized internal pointer.
+    std::string strPath;
+
+public:
+    std::unique_ptr<DbEnv> dbenv;
+    std::map<std::string, int> mapFileUseCount;
+    std::map<std::string, std::reference_wrapper<BerkeleyDatabase>> m_databases;
+    std::unordered_map<std::string, WalletDatabaseFileId> m_fileids;
+    std::condition_variable_any m_db_in_use;
+
+    BerkeleyEnvironment(const fs::path& env_directory);
+    BerkeleyEnvironment();
+    ~BerkeleyEnvironment();
+    void Reset();
+
+    bool IsMock() const { return fMockDb; }
+    bool IsInitialized() const { return fDbEnvInit; }
+    bool IsDatabaseLoaded(const std::string& db_filename) const { return m_databases.find(db_filename) != m_databases.end(); }
+    fs::path Directory() const { return strPath; }
+
+    bool Verify(const std::string& strFile);
+
+    bool Open(bool retry);
+    void Close();
+    void Flush(bool fShutdown);
+    void CheckpointLSN(const std::string& strFile);
+
+    void CloseDb(const std::string& strFile);
+    void ReloadDbEnv();
+
+    DbTxn* TxnBegin(int flags = DB_TXN_WRITE_NOSYNC)
+    {
+        DbTxn* ptxn = nullptr;
+        int ret = dbenv->txn_begin(nullptr, &ptxn, flags);
+        if (!ptxn || ret != 0)
+            return nullptr;
+        return ptxn;
+    }
+};
+
+/** Get BerkeleyEnvironment and database filename given a wallet path. */
+std::shared_ptr<BerkeleyEnvironment> GetWalletEnv(const fs::path& wallet_path, std::string& database_filename);
+
+/** Return wheter a BDB wallet database is currently loaded. */
+bool IsBDBWalletLoaded(const fs::path& wallet_path);
+
+/** An instance of this class represents one database.
+ * For BerkeleyDB this is just a (env, strFile) tuple.
+ **/
+class BerkeleyDatabase
+{
+    friend class BerkeleyBatch;
+public:
+    /** Create dummy DB handle */
+    BerkeleyDatabase() : nUpdateCounter(0), nLastSeen(0), nLastFlushed(0), nLastWalletUpdate(0), env(nullptr)
+    {
+    }
+
+    /** Create DB handle to real database */
+    BerkeleyDatabase(std::shared_ptr<BerkeleyEnvironment> env, std::string filename) :
+        nUpdateCounter(0), nLastSeen(0), nLastFlushed(0), nLastWalletUpdate(0), env(std::move(env)), strFile(std::move(filename))
+    {
+        auto inserted = this->env->m_databases.emplace(strFile, std::ref(*this));
+        assert(inserted.second);
+    }
+
+    ~BerkeleyDatabase() {
+        if (env) {
+            size_t erased = env->m_databases.erase(strFile);
+            assert(erased == 1);
+        }
+    }
+
+    /** Return object for accessing database at specified path. */
+    static std::unique_ptr<BerkeleyDatabase> Create(const fs::path& path)
+    {
+        std::string filename;
+        return MakeUnique<BerkeleyDatabase>(GetWalletEnv(path, filename), std::move(filename));
+    }
+
+    /** Return object for accessing dummy database with no read/write capabilities. */
+    static std::unique_ptr<BerkeleyDatabase> CreateDummy()
+    {
+        return MakeUnique<BerkeleyDatabase>();
+    }
+
+    /** Return object for accessing temporary in-memory database. */
+    static std::unique_ptr<BerkeleyDatabase> CreateMock()
+    {
+        return MakeUnique<BerkeleyDatabase>(std::make_shared<BerkeleyEnvironment>(), "");
+    }
+
+    /** Rewrite the entire database on disk, with the exception of key pszSkip if non-zero
+     */
+    bool Rewrite(const char* pszSkip=nullptr);
+
+    /** Back up the entire database to a file.
+     */
+    bool Backup(const std::string& strDest) const;
+
+    /** Make sure all changes are flushed to disk.
+     */
+    void Flush(bool shutdown);
+
+    void IncrementUpdateCounter();
+
+    void ReloadDbEnv();
+
+    std::atomic<unsigned int> nUpdateCounter;
+    unsigned int nLastSeen;
+    unsigned int nLastFlushed;
+    int64_t nLastWalletUpdate;
+
+    /**
+     * Pointer to shared database environment.
+     *
+     * Normally there is only one BerkeleyDatabase object per
+     * BerkeleyEnvivonment, but in the special, backwards compatible case where
+     * multiple wallet BDB data files are loaded from the same directory, this
+     * will point to a shared instance that gets freed when the last data file
+     * is closed.
+     */
+    std::shared_ptr<BerkeleyEnvironment> env;
+
+    /** Database pointer. This is initialized lazily and reset during flushes, so it can be null. */
+    std::unique_ptr<Db> m_db;
+
+private:
+    std::string strFile;
+
+    /** Return whether this database handle is a dummy for testing.
+     * Only to be used at a low level, application should ideally not care
+     * about this.
+     */
+    bool IsDummy() const { return env == nullptr; }
+};
+
+/** RAII class that provides access to a Berkeley database */
+class BerkeleyBatch
+{
+    /** RAII class that automatically cleanses its data on destruction */
+    class SafeDbt final
+    {
+        Dbt m_dbt;
+
+    public:
+        // construct Dbt with internally-managed data
+        SafeDbt();
+        // construct Dbt with provided data
+        SafeDbt(void* data, size_t size);
+        ~SafeDbt();
+
+        // delegate to Dbt
+        const void* get_data() const;
+        u_int32_t get_size() const;
+
+        // conversion operator to access the underlying Dbt
+        operator Dbt*();
+    };
+
+protected:
+    Db* pdb;
+    std::string strFile;
+    DbTxn* activeTxn;
+    bool fReadOnly;
+    bool fFlushOnClose;
+    BerkeleyEnvironment *env;
+
+public:
+    explicit BerkeleyBatch(BerkeleyDatabase& database, const char* pszMode = "r+", bool fFlushOnCloseIn=true);
+    ~BerkeleyBatch() { Close(); }
+
+    BerkeleyBatch(const BerkeleyBatch&) = delete;
+    BerkeleyBatch& operator=(const BerkeleyBatch&) = delete;
+
+    void Flush();
+    void Close();
+
+    /* flush the wallet passively (TRY_LOCK)
+       ideal to be called periodically */
+    static bool PeriodicFlush(BerkeleyDatabase& database);
+    /* verifies the database environment */
+    static bool VerifyEnvironment(const fs::path& file_path, bilingual_str& errorStr);
+    /* verifies the database file */
+    static bool VerifyDatabaseFile(const fs::path& file_path, bilingual_str& errorStr);
+
+    template <typename K, typename T>
+    bool Read(const K& key, T& value)
+    {
+        if (!pdb)
+            return false;
+
+        // Key
+        CDataStream ssKey(SER_DISK, CLIENT_VERSION);
+        ssKey.reserve(1000);
+        ssKey << key;
+        SafeDbt datKey(ssKey.data(), ssKey.size());
+
+        // Read
+        SafeDbt datValue;
+        int ret = pdb->get(activeTxn, datKey, datValue, 0);
+        bool success = false;
+        if (datValue.get_data() != nullptr) {
+            // Unserialize value
+            try {
+                CDataStream ssValue((char*)datValue.get_data(), (char*)datValue.get_data() + datValue.get_size(), SER_DISK, CLIENT_VERSION);
+                ssValue >> value;
+                success = true;
+            } catch (const std::exception&) {
+                // In this case success remains 'false'
+            }
+        }
+        return ret == 0 && success;
+    }
+
+    template <typename K, typename T>
+    bool Write(const K& key, const T& value, bool fOverwrite = true)
+    {
+        if (!pdb)
+            return true;
+        if (fReadOnly)
+            assert(!"Write called on database in read-only mode");
+
+        // Key
+        CDataStream ssKey(SER_DISK, CLIENT_VERSION);
+        ssKey.reserve(1000);
+        ssKey << key;
+        SafeDbt datKey(ssKey.data(), ssKey.size());
+
+        // Value
+        CDataStream ssValue(SER_DISK, CLIENT_VERSION);
+        ssValue.reserve(10000);
+        ssValue << value;
+        SafeDbt datValue(ssValue.data(), ssValue.size());
+
+        // Write
+        int ret = pdb->put(activeTxn, datKey, datValue, (fOverwrite ? 0 : DB_NOOVERWRITE));
+        return (ret == 0);
+    }
+
+    template <typename K>
+    bool Erase(const K& key)
+    {
+        if (!pdb)
+            return false;
+        if (fReadOnly)
+            assert(!"Erase called on database in read-only mode");
+
+        // Key
+        CDataStream ssKey(SER_DISK, CLIENT_VERSION);
+        ssKey.reserve(1000);
+        ssKey << key;
+        SafeDbt datKey(ssKey.data(), ssKey.size());
+
+        // Erase
+        int ret = pdb->del(activeTxn, datKey, 0);
+        return (ret == 0 || ret == DB_NOTFOUND);
+    }
+
+    template <typename K>
+    bool Exists(const K& key)
+    {
+        if (!pdb)
+            return false;
+
+        // Key
+        CDataStream ssKey(SER_DISK, CLIENT_VERSION);
+        ssKey.reserve(1000);
+        ssKey << key;
+        SafeDbt datKey(ssKey.data(), ssKey.size());
+
+        // Exists
+        int ret = pdb->exists(activeTxn, datKey, 0);
+        return (ret == 0);
+    }
+
+    Dbc* GetCursor();
+    int ReadAtCursor(Dbc* pcursor, CDataStream& ssKey, CDataStream& ssValue);
+    bool TxnBegin();
+    bool TxnCommit();
+    bool TxnAbort();
+
+    bool static Rewrite(BerkeleyDatabase& database, const char* pszSkip = nullptr);
+};
+
+std::string BerkeleyDatabaseVersion();
+
+#endif // BITCOIN_WALLET_BDB_H
diff --git a/src/wallet/db.cpp b/src/wallet/db.cpp
index d90e8e6433..1eb82a03c7 100644
--- a/src/wallet/db.cpp
+++ b/src/wallet/db.cpp
@@ -3,55 +3,12 @@
 // Distributed under the MIT software license, see the accompanying
 // file COPYING or http://www.opensource.org/licenses/mit-license.php.
 
+#include <fs.h>
 #include <wallet/db.h>
 
-#include <util/strencodings.h>
-#include <util/translation.h>
+#include <string>
 
-#include <stdint.h>
-
-#ifndef WIN32
-#include <sys/stat.h>
-#endif
-
-namespace {
-
-//! Make sure database has a unique fileid within the environment. If it
-//! doesn't, throw an error. BDB caches do not work properly when more than one
-//! open database has the same fileid (values written to one database may show
-//! up in reads to other databases).
-//!
-//! BerkeleyDB generates unique fileids by default
-//! (https://docs.oracle.com/cd/E17275_01/html/programmer_reference/program_copy.html),
-//! so bitcoin should never create different databases with the same fileid, but
-//! this error can be triggered if users manually copy database files.
-void CheckUniqueFileid(const BerkeleyEnvironment& env, const std::string& filename, Db& db, WalletDatabaseFileId& fileid)
-{
-    if (env.IsMock()) return;
-
-    int ret = db.get_mpf()->get_fileid(fileid.value);
-    if (ret != 0) {
-        throw std::runtime_error(strprintf("BerkeleyBatch: Can't open database %s (get_fileid failed with %d)", filename, ret));
-    }
-
-    for (const auto& item : env.m_fileids) {
-        if (fileid == item.second && &fileid != &item.second) {
-            throw std::runtime_error(strprintf("BerkeleyBatch: Can't open database %s (duplicates fileid %s from %s)", filename,
-                HexStr(std::begin(item.second.value), std::end(item.second.value)), item.first));
-        }
-    }
-}
-
-RecursiveMutex cs_db;
-std::map<std::string, std::weak_ptr<BerkeleyEnvironment>> g_dbenvs GUARDED_BY(cs_db); //!< Map from directory name to db environment.
-} // namespace
-
-bool WalletDatabaseFileId::operator==(const WalletDatabaseFileId& rhs) const
-{
-    return memcmp(value, &rhs.value, sizeof(value)) == 0;
-}
-
-static void SplitWalletPath(const fs::path& wallet_path, fs::path& env_directory, std::string& database_filename)
+void SplitWalletPath(const fs::path& wallet_path, fs::path& env_directory, std::string& database_filename)
 {
     if (fs::is_regular_file(wallet_path)) {
         // Special case for backwards compatibility: if wallet path points to an
@@ -67,18 +24,6 @@ static void SplitWalletPath(const fs::path& wallet_path, fs::path& env_directory
     }
 }
 
-bool IsWalletLoaded(const fs::path& wallet_path)
-{
-    fs::path env_directory;
-    std::string database_filename;
-    SplitWalletPath(wallet_path, env_directory, database_filename);
-    LOCK(cs_db);
-    auto env = g_dbenvs.find(env_directory.string());
-    if (env == g_dbenvs.end()) return false;
-    auto database = env->second.lock();
-    return database && database->IsDatabaseLoaded(database_filename);
-}
-
 fs::path WalletDataFilePath(const fs::path& wallet_path)
 {
     fs::path env_directory;
@@ -86,682 +31,3 @@ fs::path WalletDataFilePath(const fs::path& wallet_path)
     SplitWalletPath(wallet_path, env_directory, database_filename);
     return env_directory / database_filename;
 }
-
-/**
- * @param[in] wallet_path Path to wallet directory. Or (for backwards compatibility only) a path to a berkeley btree data file inside a wallet directory.
- * @param[out] database_filename Filename of berkeley btree data file inside the wallet directory.
- * @return A shared pointer to the BerkeleyEnvironment object for the wallet directory, never empty because ~BerkeleyEnvironment
- * erases the weak pointer from the g_dbenvs map.
- * @post A new BerkeleyEnvironment weak pointer is inserted into g_dbenvs if the directory path key was not already in the map.
- */
-std::shared_ptr<BerkeleyEnvironment> GetWalletEnv(const fs::path& wallet_path, std::string& database_filename)
-{
-    fs::path env_directory;
-    SplitWalletPath(wallet_path, env_directory, database_filename);
-    LOCK(cs_db);
-    auto inserted = g_dbenvs.emplace(env_directory.string(), std::weak_ptr<BerkeleyEnvironment>());
-    if (inserted.second) {
-        auto env = std::make_shared<BerkeleyEnvironment>(env_directory.string());
-        inserted.first->second = env;
-        return env;
-    }
-    return inserted.first->second.lock();
-}
-
-//
-// BerkeleyBatch
-//
-
-void BerkeleyEnvironment::Close()
-{
-    if (!fDbEnvInit)
-        return;
-
-    fDbEnvInit = false;
-
-    for (auto& db : m_databases) {
-        auto count = mapFileUseCount.find(db.first);
-        assert(count == mapFileUseCount.end() || count->second == 0);
-        BerkeleyDatabase& database = db.second.get();
-        if (database.m_db) {
-            database.m_db->close(0);
-            database.m_db.reset();
-        }
-    }
-
-    FILE* error_file = nullptr;
-    dbenv->get_errfile(&error_file);
-
-    int ret = dbenv->close(0);
-    if (ret != 0)
-        LogPrintf("BerkeleyEnvironment::Close: Error %d closing database environment: %s\n", ret, DbEnv::strerror(ret));
-    if (!fMockDb)
-        DbEnv((u_int32_t)0).remove(strPath.c_str(), 0);
-
-    if (error_file) fclose(error_file);
-
-    UnlockDirectory(strPath, ".walletlock");
-}
-
-void BerkeleyEnvironment::Reset()
-{
-    dbenv.reset(new DbEnv(DB_CXX_NO_EXCEPTIONS));
-    fDbEnvInit = false;
-    fMockDb = false;
-}
-
-BerkeleyEnvironment::BerkeleyEnvironment(const fs::path& dir_path) : strPath(dir_path.string())
-{
-    Reset();
-}
-
-BerkeleyEnvironment::~BerkeleyEnvironment()
-{
-    LOCK(cs_db);
-    g_dbenvs.erase(strPath);
-    Close();
-}
-
-bool BerkeleyEnvironment::Open(bool retry)
-{
-    if (fDbEnvInit) {
-        return true;
-    }
-
-    fs::path pathIn = strPath;
-    TryCreateDirectories(pathIn);
-    if (!LockDirectory(pathIn, ".walletlock")) {
-        LogPrintf("Cannot obtain a lock on wallet directory %s. Another instance of bitcoin may be using it.\n", strPath);
-        return false;
-    }
-
-    fs::path pathLogDir = pathIn / "database";
-    TryCreateDirectories(pathLogDir);
-    fs::path pathErrorFile = pathIn / "db.log";
-    LogPrintf("BerkeleyEnvironment::Open: LogDir=%s ErrorFile=%s\n", pathLogDir.string(), pathErrorFile.string());
-
-    unsigned int nEnvFlags = 0;
-    if (gArgs.GetBoolArg("-privdb", DEFAULT_WALLET_PRIVDB))
-        nEnvFlags |= DB_PRIVATE;
-
-    dbenv->set_lg_dir(pathLogDir.string().c_str());
-    dbenv->set_cachesize(0, 0x100000, 1); // 1 MiB should be enough for just the wallet
-    dbenv->set_lg_bsize(0x10000);
-    dbenv->set_lg_max(1048576);
-    dbenv->set_lk_max_locks(40000);
-    dbenv->set_lk_max_objects(40000);
-    dbenv->set_errfile(fsbridge::fopen(pathErrorFile, "a")); /// debug
-    dbenv->set_flags(DB_AUTO_COMMIT, 1);
-    dbenv->set_flags(DB_TXN_WRITE_NOSYNC, 1);
-    dbenv->log_set_config(DB_LOG_AUTO_REMOVE, 1);
-    int ret = dbenv->open(strPath.c_str(),
-                         DB_CREATE |
-                             DB_INIT_LOCK |
-                             DB_INIT_LOG |
-                             DB_INIT_MPOOL |
-                             DB_INIT_TXN |
-                             DB_THREAD |
-                             DB_RECOVER |
-                             nEnvFlags,
-                         S_IRUSR | S_IWUSR);
-    if (ret != 0) {
-        LogPrintf("BerkeleyEnvironment::Open: Error %d opening database environment: %s\n", ret, DbEnv::strerror(ret));
-        int ret2 = dbenv->close(0);
-        if (ret2 != 0) {
-            LogPrintf("BerkeleyEnvironment::Open: Error %d closing failed database environment: %s\n", ret2, DbEnv::strerror(ret2));
-        }
-        Reset();
-        if (retry) {
-            // try moving the database env out of the way
-            fs::path pathDatabaseBak = pathIn / strprintf("database.%d.bak", GetTime());
-            try {
-                fs::rename(pathLogDir, pathDatabaseBak);
-                LogPrintf("Moved old %s to %s. Retrying.\n", pathLogDir.string(), pathDatabaseBak.string());
-            } catch (const fs::filesystem_error&) {
-                // failure is ok (well, not really, but it's not worse than what we started with)
-            }
-            // try opening it again one more time
-            if (!Open(false /* retry */)) {
-                // if it still fails, it probably means we can't even create the database env
-                return false;
-            }
-        } else {
-            return false;
-        }
-    }
-
-    fDbEnvInit = true;
-    fMockDb = false;
-    return true;
-}
-
-//! Construct an in-memory mock Berkeley environment for testing
-BerkeleyEnvironment::BerkeleyEnvironment()
-{
-    Reset();
-
-    LogPrint(BCLog::WALLETDB, "BerkeleyEnvironment::MakeMock\n");
-
-    dbenv->set_cachesize(1, 0, 1);
-    dbenv->set_lg_bsize(10485760 * 4);
-    dbenv->set_lg_max(10485760);
-    dbenv->set_lk_max_locks(10000);
-    dbenv->set_lk_max_objects(10000);
-    dbenv->set_flags(DB_AUTO_COMMIT, 1);
-    dbenv->log_set_config(DB_LOG_IN_MEMORY, 1);
-    int ret = dbenv->open(nullptr,
-                         DB_CREATE |
-                             DB_INIT_LOCK |
-                             DB_INIT_LOG |
-                             DB_INIT_MPOOL |
-                             DB_INIT_TXN |
-                             DB_THREAD |
-                             DB_PRIVATE,
-                         S_IRUSR | S_IWUSR);
-    if (ret > 0) {
-        throw std::runtime_error(strprintf("BerkeleyEnvironment::MakeMock: Error %d opening database environment.", ret));
-    }
-
-    fDbEnvInit = true;
-    fMockDb = true;
-}
-
-bool BerkeleyEnvironment::Verify(const std::string& strFile)
-{
-    LOCK(cs_db);
-    assert(mapFileUseCount.count(strFile) == 0);
-
-    Db db(dbenv.get(), 0);
-    int result = db.verify(strFile.c_str(), nullptr, nullptr, 0);
-    return result == 0;
-}
-
-BerkeleyBatch::SafeDbt::SafeDbt()
-{
-    m_dbt.set_flags(DB_DBT_MALLOC);
-}
-
-BerkeleyBatch::SafeDbt::SafeDbt(void* data, size_t size)
-    : m_dbt(data, size)
-{
-}
-
-BerkeleyBatch::SafeDbt::~SafeDbt()
-{
-    if (m_dbt.get_data() != nullptr) {
-        // Clear memory, e.g. in case it was a private key
-        memory_cleanse(m_dbt.get_data(), m_dbt.get_size());
-        // under DB_DBT_MALLOC, data is malloced by the Dbt, but must be
-        // freed by the caller.
-        // https://docs.oracle.com/cd/E17275_01/html/api_reference/C/dbt.html
-        if (m_dbt.get_flags() & DB_DBT_MALLOC) {
-            free(m_dbt.get_data());
-        }
-    }
-}
-
-const void* BerkeleyBatch::SafeDbt::get_data() const
-{
-    return m_dbt.get_data();
-}
-
-u_int32_t BerkeleyBatch::SafeDbt::get_size() const
-{
-    return m_dbt.get_size();
-}
-
-BerkeleyBatch::SafeDbt::operator Dbt*()
-{
-    return &m_dbt;
-}
-
-bool BerkeleyBatch::VerifyEnvironment(const fs::path& file_path, bilingual_str& errorStr)
-{
-    std::string walletFile;
-    std::shared_ptr<BerkeleyEnvironment> env = GetWalletEnv(file_path, walletFile);
-    fs::path walletDir = env->Directory();
-
-    LogPrintf("Using BerkeleyDB version %s\n", BerkeleyDatabaseVersion());
-    LogPrintf("Using wallet %s\n", file_path.string());
-
-    if (!env->Open(true /* retry */)) {
-        errorStr = strprintf(_("Error initializing wallet database environment %s!"), walletDir);
-        return false;
-    }
-
-    return true;
-}
-
-bool BerkeleyBatch::VerifyDatabaseFile(const fs::path& file_path, bilingual_str& errorStr)
-{
-    std::string walletFile;
-    std::shared_ptr<BerkeleyEnvironment> env = GetWalletEnv(file_path, walletFile);
-    fs::path walletDir = env->Directory();
-
-    if (fs::exists(walletDir / walletFile))
-    {
-        if (!env->Verify(walletFile)) {
-            errorStr = strprintf(_("%s corrupt. Try using the wallet tool bitcoin-wallet to salvage or restoring a backup."), walletFile);
-            return false;
-        }
-    }
-    // also return true if files does not exists
-    return true;
-}
-
-void BerkeleyEnvironment::CheckpointLSN(const std::string& strFile)
-{
-    dbenv->txn_checkpoint(0, 0, 0);
-    if (fMockDb)
-        return;
-    dbenv->lsn_reset(strFile.c_str(), 0);
-}
-
-
-BerkeleyBatch::BerkeleyBatch(BerkeleyDatabase& database, const char* pszMode, bool fFlushOnCloseIn) : pdb(nullptr), activeTxn(nullptr)
-{
-    fReadOnly = (!strchr(pszMode, '+') && !strchr(pszMode, 'w'));
-    fFlushOnClose = fFlushOnCloseIn;
-    env = database.env.get();
-    if (database.IsDummy()) {
-        return;
-    }
-    const std::string &strFilename = database.strFile;
-
-    bool fCreate = strchr(pszMode, 'c') != nullptr;
-    unsigned int nFlags = DB_THREAD;
-    if (fCreate)
-        nFlags |= DB_CREATE;
-
-    {
-        LOCK(cs_db);
-        if (!env->Open(false /* retry */))
-            throw std::runtime_error("BerkeleyBatch: Failed to open database environment.");
-
-        pdb = database.m_db.get();
-        if (pdb == nullptr) {
-            int ret;
-            std::unique_ptr<Db> pdb_temp = MakeUnique<Db>(env->dbenv.get(), 0);
-
-            bool fMockDb = env->IsMock();
-            if (fMockDb) {
-                DbMpoolFile* mpf = pdb_temp->get_mpf();
-                ret = mpf->set_flags(DB_MPOOL_NOFILE, 1);
-                if (ret != 0) {
-                    throw std::runtime_error(strprintf("BerkeleyBatch: Failed to configure for no temp file backing for database %s", strFilename));
-                }
-            }
-
-            ret = pdb_temp->open(nullptr,                             // Txn pointer
-                            fMockDb ? nullptr : strFilename.c_str(),  // Filename
-                            fMockDb ? strFilename.c_str() : "main",   // Logical db name
-                            DB_BTREE,                                 // Database type
-                            nFlags,                                   // Flags
-                            0);
-
-            if (ret != 0) {
-                throw std::runtime_error(strprintf("BerkeleyBatch: Error %d, can't open database %s", ret, strFilename));
-            }
-
-            // Call CheckUniqueFileid on the containing BDB environment to
-            // avoid BDB data consistency bugs that happen when different data
-            // files in the same environment have the same fileid.
-            //
-            // Also call CheckUniqueFileid on all the other g_dbenvs to prevent
-            // bitcoin from opening the same data file through another
-            // environment when the file is referenced through equivalent but
-            // not obviously identical symlinked or hard linked or bind mounted
-            // paths. In the future a more relaxed check for equal inode and
-            // device ids could be done instead, which would allow opening
-            // different backup copies of a wallet at the same time. Maybe even
-            // more ideally, an exclusive lock for accessing the database could
-            // be implemented, so no equality checks are needed at all. (Newer
-            // versions of BDB have an set_lk_exclusive method for this
-            // purpose, but the older version we use does not.)
-            for (const auto& env : g_dbenvs) {
-                CheckUniqueFileid(*env.second.lock().get(), strFilename, *pdb_temp, this->env->m_fileids[strFilename]);
-            }
-
-            pdb = pdb_temp.release();
-            database.m_db.reset(pdb);
-
-            if (fCreate && !Exists(std::string("version"))) {
-                bool fTmp = fReadOnly;
-                fReadOnly = false;
-                Write(std::string("version"), CLIENT_VERSION);
-                fReadOnly = fTmp;
-            }
-        }
-        ++env->mapFileUseCount[strFilename];
-        strFile = strFilename;
-    }
-}
-
-void BerkeleyBatch::Flush()
-{
-    if (activeTxn)
-        return;
-
-    // Flush database activity from memory pool to disk log
-    unsigned int nMinutes = 0;
-    if (fReadOnly)
-        nMinutes = 1;
-
-    if (env) { // env is nullptr for dummy databases (i.e. in tests). Don't actually flush if env is nullptr so we don't segfault
-        env->dbenv->txn_checkpoint(nMinutes ? gArgs.GetArg("-dblogsize", DEFAULT_WALLET_DBLOGSIZE) * 1024 : 0, nMinutes, 0);
-    }
-}
-
-void BerkeleyDatabase::IncrementUpdateCounter()
-{
-    ++nUpdateCounter;
-}
-
-void BerkeleyBatch::Close()
-{
-    if (!pdb)
-        return;
-    if (activeTxn)
-        activeTxn->abort();
-    activeTxn = nullptr;
-    pdb = nullptr;
-
-    if (fFlushOnClose)
-        Flush();
-
-    {
-        LOCK(cs_db);
-        --env->mapFileUseCount[strFile];
-    }
-    env->m_db_in_use.notify_all();
-}
-
-void BerkeleyEnvironment::CloseDb(const std::string& strFile)
-{
-    {
-        LOCK(cs_db);
-        auto it = m_databases.find(strFile);
-        assert(it != m_databases.end());
-        BerkeleyDatabase& database = it->second.get();
-        if (database.m_db) {
-            // Close the database handle
-            database.m_db->close(0);
-            database.m_db.reset();
-        }
-    }
-}
-
-void BerkeleyEnvironment::ReloadDbEnv()
-{
-    // Make sure that no Db's are in use
-    AssertLockNotHeld(cs_db);
-    std::unique_lock<RecursiveMutex> lock(cs_db);
-    m_db_in_use.wait(lock, [this](){
-        for (auto& count : mapFileUseCount) {
-            if (count.second > 0) return false;
-        }
-        return true;
-    });
-
-    std::vector<std::string> filenames;
-    for (auto it : m_databases) {
-        filenames.push_back(it.first);
-    }
-    // Close the individual Db's
-    for (const std::string& filename : filenames) {
-        CloseDb(filename);
-    }
-    // Reset the environment
-    Flush(true); // This will flush and close the environment
-    Reset();
-    Open(true);
-}
-
-bool BerkeleyBatch::Rewrite(BerkeleyDatabase& database, const char* pszSkip)
-{
-    if (database.IsDummy()) {
-        return true;
-    }
-    BerkeleyEnvironment *env = database.env.get();
-    const std::string& strFile = database.strFile;
-    while (true) {
-        {
-            LOCK(cs_db);
-            if (!env->mapFileUseCount.count(strFile) || env->mapFileUseCount[strFile] == 0) {
-                // Flush log data to the dat file
-                env->CloseDb(strFile);
-                env->CheckpointLSN(strFile);
-                env->mapFileUseCount.erase(strFile);
-
-                bool fSuccess = true;
-                LogPrintf("BerkeleyBatch::Rewrite: Rewriting %s...\n", strFile);
-                std::string strFileRes = strFile + ".rewrite";
-                { // surround usage of db with extra {}
-                    BerkeleyBatch db(database, "r");
-                    std::unique_ptr<Db> pdbCopy = MakeUnique<Db>(env->dbenv.get(), 0);
-
-                    int ret = pdbCopy->open(nullptr,               // Txn pointer
-                                            strFileRes.c_str(), // Filename
-                                            "main",             // Logical db name
-                                            DB_BTREE,           // Database type
-                                            DB_CREATE,          // Flags
-                                            0);
-                    if (ret > 0) {
-                        LogPrintf("BerkeleyBatch::Rewrite: Can't create database file %s\n", strFileRes);
-                        fSuccess = false;
-                    }
-
-                    Dbc* pcursor = db.GetCursor();
-                    if (pcursor)
-                        while (fSuccess) {
-                            CDataStream ssKey(SER_DISK, CLIENT_VERSION);
-                            CDataStream ssValue(SER_DISK, CLIENT_VERSION);
-                            int ret1 = db.ReadAtCursor(pcursor, ssKey, ssValue);
-                            if (ret1 == DB_NOTFOUND) {
-                                pcursor->close();
-                                break;
-                            } else if (ret1 != 0) {
-                                pcursor->close();
-                                fSuccess = false;
-                                break;
-                            }
-                            if (pszSkip &&
-                                strncmp(ssKey.data(), pszSkip, std::min(ssKey.size(), strlen(pszSkip))) == 0)
-                                continue;
-                            if (strncmp(ssKey.data(), "\x07version", 8) == 0) {
-                                // Update version:
-                                ssValue.clear();
-                                ssValue << CLIENT_VERSION;
-                            }
-                            Dbt datKey(ssKey.data(), ssKey.size());
-                            Dbt datValue(ssValue.data(), ssValue.size());
-                            int ret2 = pdbCopy->put(nullptr, &datKey, &datValue, DB_NOOVERWRITE);
-                            if (ret2 > 0)
-                                fSuccess = false;
-                        }
-                    if (fSuccess) {
-                        db.Close();
-                        env->CloseDb(strFile);
-                        if (pdbCopy->close(0))
-                            fSuccess = false;
-                    } else {
-                        pdbCopy->close(0);
-                    }
-                }
-                if (fSuccess) {
-                    Db dbA(env->dbenv.get(), 0);
-                    if (dbA.remove(strFile.c_str(), nullptr, 0))
-                        fSuccess = false;
-                    Db dbB(env->dbenv.get(), 0);
-                    if (dbB.rename(strFileRes.c_str(), nullptr, strFile.c_str(), 0))
-                        fSuccess = false;
-                }
-                if (!fSuccess)
-                    LogPrintf("BerkeleyBatch::Rewrite: Failed to rewrite database file %s\n", strFileRes);
-                return fSuccess;
-            }
-        }
-        UninterruptibleSleep(std::chrono::milliseconds{100});
-    }
-}
-
-
-void BerkeleyEnvironment::Flush(bool fShutdown)
-{
-    int64_t nStart = GetTimeMillis();
-    // Flush log data to the actual data file on all files that are not in use
-    LogPrint(BCLog::WALLETDB, "BerkeleyEnvironment::Flush: [%s] Flush(%s)%s\n", strPath, fShutdown ? "true" : "false", fDbEnvInit ? "" : " database not started");
-    if (!fDbEnvInit)
-        return;
-    {
-        LOCK(cs_db);
-        std::map<std::string, int>::iterator mi = mapFileUseCount.begin();
-        while (mi != mapFileUseCount.end()) {
-            std::string strFile = (*mi).first;
-            int nRefCount = (*mi).second;
-            LogPrint(BCLog::WALLETDB, "BerkeleyEnvironment::Flush: Flushing %s (refcount = %d)...\n", strFile, nRefCount);
-            if (nRefCount == 0) {
-                // Move log data to the dat file
-                CloseDb(strFile);
-                LogPrint(BCLog::WALLETDB, "BerkeleyEnvironment::Flush: %s checkpoint\n", strFile);
-                dbenv->txn_checkpoint(0, 0, 0);
-                LogPrint(BCLog::WALLETDB, "BerkeleyEnvironment::Flush: %s detach\n", strFile);
-                if (!fMockDb)
-                    dbenv->lsn_reset(strFile.c_str(), 0);
-                LogPrint(BCLog::WALLETDB, "BerkeleyEnvironment::Flush: %s closed\n", strFile);
-                mapFileUseCount.erase(mi++);
-            } else
-                mi++;
-        }
-        LogPrint(BCLog::WALLETDB, "BerkeleyEnvironment::Flush: Flush(%s)%s took %15dms\n", fShutdown ? "true" : "false", fDbEnvInit ? "" : " database not started", GetTimeMillis() - nStart);
-        if (fShutdown) {
-            char** listp;
-            if (mapFileUseCount.empty()) {
-                dbenv->log_archive(&listp, DB_ARCH_REMOVE);
-                Close();
-                if (!fMockDb) {
-                    fs::remove_all(fs::path(strPath) / "database");
-                }
-            }
-        }
-    }
-}
-
-bool BerkeleyBatch::PeriodicFlush(BerkeleyDatabase& database)
-{
-    if (database.IsDummy()) {
-        return true;
-    }
-    bool ret = false;
-    BerkeleyEnvironment *env = database.env.get();
-    const std::string& strFile = database.strFile;
-    TRY_LOCK(cs_db, lockDb);
-    if (lockDb)
-    {
-        // Don't do this if any databases are in use
-        int nRefCount = 0;
-        std::map<std::string, int>::iterator mit = env->mapFileUseCount.begin();
-        while (mit != env->mapFileUseCount.end())
-        {
-            nRefCount += (*mit).second;
-            mit++;
-        }
-
-        if (nRefCount == 0)
-        {
-            std::map<std::string, int>::iterator mi = env->mapFileUseCount.find(strFile);
-            if (mi != env->mapFileUseCount.end())
-            {
-                LogPrint(BCLog::WALLETDB, "Flushing %s\n", strFile);
-                int64_t nStart = GetTimeMillis();
-
-                // Flush wallet file so it's self contained
-                env->CloseDb(strFile);
-                env->CheckpointLSN(strFile);
-
-                env->mapFileUseCount.erase(mi++);
-                LogPrint(BCLog::WALLETDB, "Flushed %s %dms\n", strFile, GetTimeMillis() - nStart);
-                ret = true;
-            }
-        }
-    }
-
-    return ret;
-}
-
-bool BerkeleyDatabase::Rewrite(const char* pszSkip)
-{
-    return BerkeleyBatch::Rewrite(*this, pszSkip);
-}
-
-bool BerkeleyDatabase::Backup(const std::string& strDest) const
-{
-    if (IsDummy()) {
-        return false;
-    }
-    while (true)
-    {
-        {
-            LOCK(cs_db);
-            if (!env->mapFileUseCount.count(strFile) || env->mapFileUseCount[strFile] == 0)
-            {
-                // Flush log data to the dat file
-                env->CloseDb(strFile);
-                env->CheckpointLSN(strFile);
-                env->mapFileUseCount.erase(strFile);
-
-                // Copy wallet file
-                fs::path pathSrc = env->Directory() / strFile;
-                fs::path pathDest(strDest);
-                if (fs::is_directory(pathDest))
-                    pathDest /= strFile;
-
-                try {
-                    if (fs::equivalent(pathSrc, pathDest)) {
-                        LogPrintf("cannot backup to wallet source file %s\n", pathDest.string());
-                        return false;
-                    }
-
-                    fs::copy_file(pathSrc, pathDest, fs::copy_option::overwrite_if_exists);
-                    LogPrintf("copied %s to %s\n", strFile, pathDest.string());
-                    return true;
-                } catch (const fs::filesystem_error& e) {
-                    LogPrintf("error copying %s to %s - %s\n", strFile, pathDest.string(), fsbridge::get_filesystem_error_message(e));
-                    return false;
-                }
-            }
-        }
-        UninterruptibleSleep(std::chrono::milliseconds{100});
-    }
-}
-
-void BerkeleyDatabase::Flush(bool shutdown)
-{
-    if (!IsDummy()) {
-        env->Flush(shutdown);
-        if (shutdown) {
-            LOCK(cs_db);
-            g_dbenvs.erase(env->Directory().string());
-            env = nullptr;
-        } else {
-            // TODO: To avoid g_dbenvs.erase erasing the environment prematurely after the
-            // first database shutdown when multiple databases are open in the same
-            // environment, should replace raw database `env` pointers with shared or weak
-            // pointers, or else separate the database and environment shutdowns so
-            // environments can be shut down after databases.
-            env->m_fileids.erase(strFile);
-        }
-    }
-}
-
-void BerkeleyDatabase::ReloadDbEnv()
-{
-    if (!IsDummy()) {
-        env->ReloadDbEnv();
-    }
-}
-
-std::string BerkeleyDatabaseVersion()
-{
-    return DbEnv::version(nullptr, nullptr, nullptr);
-}
diff --git a/src/wallet/db.h b/src/wallet/db.h
index 54ce144ffc..1322bf54fa 100644
--- a/src/wallet/db.h
+++ b/src/wallet/db.h
@@ -6,389 +6,12 @@
 #ifndef BITCOIN_WALLET_DB_H
 #define BITCOIN_WALLET_DB_H
 
-#include <clientversion.h>
 #include <fs.h>
-#include <serialize.h>
-#include <streams.h>
-#include <util/system.h>
 
-#include <atomic>
-#include <map>
-#include <memory>
 #include <string>
-#include <unordered_map>
-#include <vector>
-
-#if defined(__GNUC__) && !defined(__clang__)
-#pragma GCC diagnostic push
-#pragma GCC diagnostic ignored "-Wsuggest-override"
-#endif
-#include <db_cxx.h>
-#if defined(__GNUC__) && !defined(__clang__)
-#pragma GCC diagnostic pop
-#endif
-
-struct bilingual_str;
-
-static const unsigned int DEFAULT_WALLET_DBLOGSIZE = 100;
-static const bool DEFAULT_WALLET_PRIVDB = true;
-
-struct WalletDatabaseFileId {
-    u_int8_t value[DB_FILE_ID_LEN];
-    bool operator==(const WalletDatabaseFileId& rhs) const;
-};
-
-class BerkeleyDatabase;
-
-class BerkeleyEnvironment
-{
-private:
-    bool fDbEnvInit;
-    bool fMockDb;
-    // Don't change into fs::path, as that can result in
-    // shutdown problems/crashes caused by a static initialized internal pointer.
-    std::string strPath;
-
-public:
-    std::unique_ptr<DbEnv> dbenv;
-    std::map<std::string, int> mapFileUseCount;
-    std::map<std::string, std::reference_wrapper<BerkeleyDatabase>> m_databases;
-    std::unordered_map<std::string, WalletDatabaseFileId> m_fileids;
-    std::condition_variable_any m_db_in_use;
-
-    BerkeleyEnvironment(const fs::path& env_directory);
-    BerkeleyEnvironment();
-    ~BerkeleyEnvironment();
-    void Reset();
-
-    bool IsMock() const { return fMockDb; }
-    bool IsInitialized() const { return fDbEnvInit; }
-    bool IsDatabaseLoaded(const std::string& db_filename) const { return m_databases.find(db_filename) != m_databases.end(); }
-    fs::path Directory() const { return strPath; }
-
-    bool Verify(const std::string& strFile);
-
-    bool Open(bool retry);
-    void Close();
-    void Flush(bool fShutdown);
-    void CheckpointLSN(const std::string& strFile);
-
-    void CloseDb(const std::string& strFile);
-    void ReloadDbEnv();
-
-    DbTxn* TxnBegin(int flags = DB_TXN_WRITE_NOSYNC)
-    {
-        DbTxn* ptxn = nullptr;
-        int ret = dbenv->txn_begin(nullptr, &ptxn, flags);
-        if (!ptxn || ret != 0)
-            return nullptr;
-        return ptxn;
-    }
-};
-
-/** Return whether a wallet database is currently loaded. */
-bool IsWalletLoaded(const fs::path& wallet_path);
 
 /** Given a wallet directory path or legacy file path, return path to main data file in the wallet database. */
 fs::path WalletDataFilePath(const fs::path& wallet_path);
-
-/** Get BerkeleyEnvironment and database filename given a wallet path. */
-std::shared_ptr<BerkeleyEnvironment> GetWalletEnv(const fs::path& wallet_path, std::string& database_filename);
-
-/** An instance of this class represents one database.
- * For BerkeleyDB this is just a (env, strFile) tuple.
- **/
-class BerkeleyDatabase
-{
-    friend class BerkeleyBatch;
-public:
-    /** Create dummy DB handle */
-    BerkeleyDatabase() : nUpdateCounter(0), nLastSeen(0), nLastFlushed(0), nLastWalletUpdate(0), env(nullptr)
-    {
-    }
-
-    /** Create DB handle to real database */
-    BerkeleyDatabase(std::shared_ptr<BerkeleyEnvironment> env, std::string filename) :
-        nUpdateCounter(0), nLastSeen(0), nLastFlushed(0), nLastWalletUpdate(0), env(std::move(env)), strFile(std::move(filename))
-    {
-        auto inserted = this->env->m_databases.emplace(strFile, std::ref(*this));
-        assert(inserted.second);
-    }
-
-    ~BerkeleyDatabase() {
-        if (env) {
-            size_t erased = env->m_databases.erase(strFile);
-            assert(erased == 1);
-        }
-    }
-
-    /** Return object for accessing database at specified path. */
-    static std::unique_ptr<BerkeleyDatabase> Create(const fs::path& path)
-    {
-        std::string filename;
-        return MakeUnique<BerkeleyDatabase>(GetWalletEnv(path, filename), std::move(filename));
-    }
-
-    /** Return object for accessing dummy database with no read/write capabilities. */
-    static std::unique_ptr<BerkeleyDatabase> CreateDummy()
-    {
-        return MakeUnique<BerkeleyDatabase>();
-    }
-
-    /** Return object for accessing temporary in-memory database. */
-    static std::unique_ptr<BerkeleyDatabase> CreateMock()
-    {
-        return MakeUnique<BerkeleyDatabase>(std::make_shared<BerkeleyEnvironment>(), "");
-    }
-
-    /** Rewrite the entire database on disk, with the exception of key pszSkip if non-zero
-     */
-    bool Rewrite(const char* pszSkip=nullptr);
-
-    /** Back up the entire database to a file.
-     */
-    bool Backup(const std::string& strDest) const;
-
-    /** Make sure all changes are flushed to disk.
-     */
-    void Flush(bool shutdown);
-
-    void IncrementUpdateCounter();
-
-    void ReloadDbEnv();
-
-    std::atomic<unsigned int> nUpdateCounter;
-    unsigned int nLastSeen;
-    unsigned int nLastFlushed;
-    int64_t nLastWalletUpdate;
-
-    /**
-     * Pointer to shared database environment.
-     *
-     * Normally there is only one BerkeleyDatabase object per
-     * BerkeleyEnvivonment, but in the special, backwards compatible case where
-     * multiple wallet BDB data files are loaded from the same directory, this
-     * will point to a shared instance that gets freed when the last data file
-     * is closed.
-     */
-    std::shared_ptr<BerkeleyEnvironment> env;
-
-    /** Database pointer. This is initialized lazily and reset during flushes, so it can be null. */
-    std::unique_ptr<Db> m_db;
-
-private:
-    std::string strFile;
-
-    /** Return whether this database handle is a dummy for testing.
-     * Only to be used at a low level, application should ideally not care
-     * about this.
-     */
-    bool IsDummy() const { return env == nullptr; }
-};
-
-/** RAII class that provides access to a Berkeley database */
-class BerkeleyBatch
-{
-    /** RAII class that automatically cleanses its data on destruction */
-    class SafeDbt final
-    {
-        Dbt m_dbt;
-
-    public:
-        // construct Dbt with internally-managed data
-        SafeDbt();
-        // construct Dbt with provided data
-        SafeDbt(void* data, size_t size);
-        ~SafeDbt();
-
-        // delegate to Dbt
-        const void* get_data() const;
-        u_int32_t get_size() const;
-
-        // conversion operator to access the underlying Dbt
-        operator Dbt*();
-    };
-
-protected:
-    Db* pdb;
-    std::string strFile;
-    DbTxn* activeTxn;
-    bool fReadOnly;
-    bool fFlushOnClose;
-    BerkeleyEnvironment *env;
-
-public:
-    explicit BerkeleyBatch(BerkeleyDatabase& database, const char* pszMode = "r+", bool fFlushOnCloseIn=true);
-    ~BerkeleyBatch() { Close(); }
-
-    BerkeleyBatch(const BerkeleyBatch&) = delete;
-    BerkeleyBatch& operator=(const BerkeleyBatch&) = delete;
-
-    void Flush();
-    void Close();
-
-    /* flush the wallet passively (TRY_LOCK)
-       ideal to be called periodically */
-    static bool PeriodicFlush(BerkeleyDatabase& database);
-    /* verifies the database environment */
-    static bool VerifyEnvironment(const fs::path& file_path, bilingual_str& errorStr);
-    /* verifies the database file */
-    static bool VerifyDatabaseFile(const fs::path& file_path, bilingual_str& errorStr);
-
-    template <typename K, typename T>
-    bool Read(const K& key, T& value)
-    {
-        if (!pdb)
-            return false;
-
-        // Key
-        CDataStream ssKey(SER_DISK, CLIENT_VERSION);
-        ssKey.reserve(1000);
-        ssKey << key;
-        SafeDbt datKey(ssKey.data(), ssKey.size());
-
-        // Read
-        SafeDbt datValue;
-        int ret = pdb->get(activeTxn, datKey, datValue, 0);
-        bool success = false;
-        if (datValue.get_data() != nullptr) {
-            // Unserialize value
-            try {
-                CDataStream ssValue((char*)datValue.get_data(), (char*)datValue.get_data() + datValue.get_size(), SER_DISK, CLIENT_VERSION);
-                ssValue >> value;
-                success = true;
-            } catch (const std::exception&) {
-                // In this case success remains 'false'
-            }
-        }
-        return ret == 0 && success;
-    }
-
-    template <typename K, typename T>
-    bool Write(const K& key, const T& value, bool fOverwrite = true)
-    {
-        if (!pdb)
-            return true;
-        if (fReadOnly)
-            assert(!"Write called on database in read-only mode");
-
-        // Key
-        CDataStream ssKey(SER_DISK, CLIENT_VERSION);
-        ssKey.reserve(1000);
-        ssKey << key;
-        SafeDbt datKey(ssKey.data(), ssKey.size());
-
-        // Value
-        CDataStream ssValue(SER_DISK, CLIENT_VERSION);
-        ssValue.reserve(10000);
-        ssValue << value;
-        SafeDbt datValue(ssValue.data(), ssValue.size());
-
-        // Write
-        int ret = pdb->put(activeTxn, datKey, datValue, (fOverwrite ? 0 : DB_NOOVERWRITE));
-        return (ret == 0);
-    }
-
-    template <typename K>
-    bool Erase(const K& key)
-    {
-        if (!pdb)
-            return false;
-        if (fReadOnly)
-            assert(!"Erase called on database in read-only mode");
-
-        // Key
-        CDataStream ssKey(SER_DISK, CLIENT_VERSION);
-        ssKey.reserve(1000);
-        ssKey << key;
-        SafeDbt datKey(ssKey.data(), ssKey.size());
-
-        // Erase
-        int ret = pdb->del(activeTxn, datKey, 0);
-        return (ret == 0 || ret == DB_NOTFOUND);
-    }
-
-    template <typename K>
-    bool Exists(const K& key)
-    {
-        if (!pdb)
-            return false;
-
-        // Key
-        CDataStream ssKey(SER_DISK, CLIENT_VERSION);
-        ssKey.reserve(1000);
-        ssKey << key;
-        SafeDbt datKey(ssKey.data(), ssKey.size());
-
-        // Exists
-        int ret = pdb->exists(activeTxn, datKey, 0);
-        return (ret == 0);
-    }
-
-    Dbc* GetCursor()
-    {
-        if (!pdb)
-            return nullptr;
-        Dbc* pcursor = nullptr;
-        int ret = pdb->cursor(nullptr, &pcursor, 0);
-        if (ret != 0)
-            return nullptr;
-        return pcursor;
-    }
-
-    int ReadAtCursor(Dbc* pcursor, CDataStream& ssKey, CDataStream& ssValue)
-    {
-        // Read at cursor
-        SafeDbt datKey;
-        SafeDbt datValue;
-        int ret = pcursor->get(datKey, datValue, DB_NEXT);
-        if (ret != 0)
-            return ret;
-        else if (datKey.get_data() == nullptr || datValue.get_data() == nullptr)
-            return 99999;
-
-        // Convert to streams
-        ssKey.SetType(SER_DISK);
-        ssKey.clear();
-        ssKey.write((char*)datKey.get_data(), datKey.get_size());
-        ssValue.SetType(SER_DISK);
-        ssValue.clear();
-        ssValue.write((char*)datValue.get_data(), datValue.get_size());
-        return 0;
-    }
-
-    bool TxnBegin()
-    {
-        if (!pdb || activeTxn)
-            return false;
-        DbTxn* ptxn = env->TxnBegin();
-        if (!ptxn)
-            return false;
-        activeTxn = ptxn;
-        return true;
-    }
-
-    bool TxnCommit()
-    {
-        if (!pdb || !activeTxn)
-            return false;
-        int ret = activeTxn->commit(0);
-        activeTxn = nullptr;
-        return (ret == 0);
-    }
-
-    bool TxnAbort()
-    {
-        if (!pdb || !activeTxn)
-            return false;
-        int ret = activeTxn->abort();
-        activeTxn = nullptr;
-        return (ret == 0);
-    }
-
-    bool static Rewrite(BerkeleyDatabase& database, const char* pszSkip = nullptr);
-};
-
-std::string BerkeleyDatabaseVersion();
+void SplitWalletPath(const fs::path& wallet_path, fs::path& env_directory, std::string& database_filename);
 
 #endif // BITCOIN_WALLET_DB_H
diff --git a/src/wallet/test/db_tests.cpp b/src/wallet/test/db_tests.cpp
index f4a4c9fa7c..8f0083cd2e 100644
--- a/src/wallet/test/db_tests.cpp
+++ b/src/wallet/test/db_tests.cpp
@@ -8,7 +8,7 @@
 
 #include <fs.h>
 #include <test/util/setup_common.h>
-#include <wallet/db.h>
+#include <wallet/bdb.h>
 
 
 BOOST_FIXTURE_TEST_SUITE(db_tests, BasicTestingSetup)
diff --git a/src/wallet/walletdb.cpp b/src/wallet/walletdb.cpp
index cb516f70f0..2f6c2b883a 100644
--- a/src/wallet/walletdb.cpp
+++ b/src/wallet/walletdb.cpp
@@ -1018,3 +1018,8 @@ bool WalletBatch::TxnAbort()
 {
     return m_batch.TxnAbort();
 }
+
+bool IsWalletLoaded(const fs::path& wallet_path)
+{
+    return IsBDBWalletLoaded(wallet_path);
+}
diff --git a/src/wallet/walletdb.h b/src/wallet/walletdb.h
index b95ed24d12..1037bd579f 100644
--- a/src/wallet/walletdb.h
+++ b/src/wallet/walletdb.h
@@ -8,6 +8,7 @@
 
 #include <amount.h>
 #include <script/sign.h>
+#include <wallet/bdb.h>
 #include <wallet/db.h>
 #include <wallet/walletutil.h>
 #include <key.h>
@@ -289,4 +290,7 @@ void MaybeCompactWalletDB();
 //! Unserialize a given Key-Value pair and load it into the wallet
 bool ReadKeyValue(CWallet* pwallet, CDataStream& ssKey, CDataStream& ssValue, std::string& strType, std::string& strErr);
 
+/** Return whether a wallet database is currently loaded. */
+bool IsWalletLoaded(const fs::path& wallet_path);
+
 #endif // BITCOIN_WALLET_WALLETDB_H