Merge #9951: Wallet database handling abstractions/simplifications

911a480 wallet: Add comment describing the various classes in walletdb.h (Wladimir J. van der Laan)
69d2e9b wallet: Make IsDummy private in CWalletDBWrapper (Wladimir J. van der Laan)
3323281 wallet: CWalletDB CDB composition not inheritance (Wladimir J. van der Laan)
be9e1a9 wallet: Reduce references to global bitdb environment (Wladimir J. van der Laan)
071c955 wallet: Get rid of fFileBacked (Wladimir J. van der Laan)
71afe3c wallet: Introduce database handle wrapper (Wladimir J. van der Laan)

Tree-SHA512: e4e72953c61a2f6995d609a32f8ed8e18cab9a92bc9e193d46a1d1f06d9daa5c6da6fce2867d4e3ba4fc0439141901a3d35f246486f0fa8f59587786379dfcbd

9 files changed, 355 insertions, 242 deletions

diff --git a/src/qt/test/wallettests.cpp b/src/qt/test/wallettests.cpp
index f794b6b382..a0dce3d997 100644
--- a/src/qt/test/wallettests.cpp
+++ b/src/qt/test/wallettests.cpp
@@ -86,7 +86,8 @@ void WalletTests::walletTests()
     TestChain100Setup test;
     test.CreateAndProcessBlock({}, GetScriptForRawPubKey(test.coinbaseKey.GetPubKey()));
     bitdb.MakeMock();
-    CWallet wallet("wallet_test.dat");
+    std::unique_ptr<CWalletDBWrapper> dbw(new CWalletDBWrapper(&bitdb, "wallet_test.dat"));
+    CWallet wallet(std::move(dbw));
     bool firstRun;
     wallet.LoadWallet(firstRun);
     {
diff --git a/src/wallet/db.cpp b/src/wallet/db.cpp
index f47fc92b57..c810476f96 100644
--- a/src/wallet/db.cpp
+++ b/src/wallet/db.cpp
@@ -359,13 +359,16 @@ void CDBEnv::CheckpointLSN(const std::string& strFile)
 }
 
 
-CDB::CDB(const std::string& strFilename, const char* pszMode, bool fFlushOnCloseIn) : pdb(NULL), activeTxn(NULL)
+CDB::CDB(CWalletDBWrapper& dbw, const char* pszMode, bool fFlushOnCloseIn) : pdb(NULL), activeTxn(NULL)
 {
     int ret;
     fReadOnly = (!strchr(pszMode, '+') && !strchr(pszMode, 'w'));
     fFlushOnClose = fFlushOnCloseIn;
-    if (strFilename.empty())
+    env = dbw.env;
+    if (dbw.IsDummy()) {
         return;
+    }
+    const std::string &strFilename = dbw.strFile;
 
     bool fCreate = strchr(pszMode, 'c') != NULL;
     unsigned int nFlags = DB_THREAD;
@@ -373,17 +376,17 @@ CDB::CDB(const std::string& strFilename, const char* pszMode, bool fFlushOnClose
         nFlags |= DB_CREATE;
 
     {
-        LOCK(bitdb.cs_db);
-        if (!bitdb.Open(GetDataDir()))
+        LOCK(env->cs_db);
+        if (!env->Open(GetDataDir()))
             throw std::runtime_error("CDB: Failed to open database environment.");
 
         strFile = strFilename;
-        ++bitdb.mapFileUseCount[strFile];
-        pdb = bitdb.mapDb[strFile];
+        ++env->mapFileUseCount[strFile];
+        pdb = env->mapDb[strFile];
         if (pdb == NULL) {
-            pdb = new Db(bitdb.dbenv, 0);
+            pdb = new Db(env->dbenv, 0);
 
-            bool fMockDb = bitdb.IsMock();
+            bool fMockDb = env->IsMock();
             if (fMockDb) {
                 DbMpoolFile* mpf = pdb->get_mpf();
                 ret = mpf->set_flags(DB_MPOOL_NOFILE, 1);
@@ -401,7 +404,7 @@ CDB::CDB(const std::string& strFilename, const char* pszMode, bool fFlushOnClose
             if (ret != 0) {
                 delete pdb;
                 pdb = NULL;
-                --bitdb.mapFileUseCount[strFile];
+                --env->mapFileUseCount[strFile];
                 strFile = "";
                 throw std::runtime_error(strprintf("CDB: Error %d, can't open database %s", ret, strFilename));
             }
@@ -413,7 +416,7 @@ CDB::CDB(const std::string& strFilename, const char* pszMode, bool fFlushOnClose
                 fReadOnly = fTmp;
             }
 
-            bitdb.mapDb[strFile] = pdb;
+            env->mapDb[strFile] = pdb;
         }
     }
 }
@@ -428,7 +431,7 @@ void CDB::Flush()
     if (fReadOnly)
         nMinutes = 1;
 
-    bitdb.dbenv->txn_checkpoint(nMinutes ? GetArg("-dblogsize", DEFAULT_WALLET_DBLOGSIZE) * 1024 : 0, nMinutes, 0);
+    env->dbenv->txn_checkpoint(nMinutes ? GetArg("-dblogsize", DEFAULT_WALLET_DBLOGSIZE) * 1024 : 0, nMinutes, 0);
 }
 
 void CDB::Close()
@@ -444,8 +447,8 @@ void CDB::Close()
         Flush();
 
     {
-        LOCK(bitdb.cs_db);
-        --bitdb.mapFileUseCount[strFile];
+        LOCK(env->cs_db);
+        --env->mapFileUseCount[strFile];
     }
 }
 
@@ -472,23 +475,28 @@ bool CDBEnv::RemoveDb(const std::string& strFile)
     return (rc == 0);
 }
 
-bool CDB::Rewrite(const std::string& strFile, const char* pszSkip)
+bool CDB::Rewrite(CWalletDBWrapper& dbw, const char* pszSkip)
 {
+    if (dbw.IsDummy()) {
+        return true;
+    }
+    CDBEnv *env = dbw.env;
+    const std::string& strFile = dbw.strFile;
     while (true) {
         {
-            LOCK(bitdb.cs_db);
-            if (!bitdb.mapFileUseCount.count(strFile) || bitdb.mapFileUseCount[strFile] == 0) {
+            LOCK(env->cs_db);
+            if (!env->mapFileUseCount.count(strFile) || env->mapFileUseCount[strFile] == 0) {
                 // Flush log data to the dat file
-                bitdb.CloseDb(strFile);
-                bitdb.CheckpointLSN(strFile);
-                bitdb.mapFileUseCount.erase(strFile);
+                env->CloseDb(strFile);
+                env->CheckpointLSN(strFile);
+                env->mapFileUseCount.erase(strFile);
 
                 bool fSuccess = true;
                 LogPrintf("CDB::Rewrite: Rewriting %s...\n", strFile);
                 std::string strFileRes = strFile + ".rewrite";
                 { // surround usage of db with extra {}
-                    CDB db(strFile.c_str(), "r");
-                    Db* pdbCopy = new Db(bitdb.dbenv, 0);
+                    CDB db(dbw, "r");
+                    Db* pdbCopy = new Db(env->dbenv, 0);
 
                     int ret = pdbCopy->open(NULL,               // Txn pointer
                                             strFileRes.c_str(), // Filename
@@ -531,17 +539,17 @@ bool CDB::Rewrite(const std::string& strFile, const char* pszSkip)
                         }
                     if (fSuccess) {
                         db.Close();
-                        bitdb.CloseDb(strFile);
+                        env->CloseDb(strFile);
                         if (pdbCopy->close(0))
                             fSuccess = false;
                         delete pdbCopy;
                     }
                 }
                 if (fSuccess) {
-                    Db dbA(bitdb.dbenv, 0);
+                    Db dbA(env->dbenv, 0);
                     if (dbA.remove(strFile.c_str(), NULL, 0))
                         fSuccess = false;
-                    Db dbB(bitdb.dbenv, 0);
+                    Db dbB(env->dbenv, 0);
                     if (dbB.rename(strFileRes.c_str(), NULL, strFile.c_str(), 0))
                         fSuccess = false;
                 }
@@ -596,16 +604,21 @@ void CDBEnv::Flush(bool fShutdown)
     }
 }
 
-bool CDB::PeriodicFlush(std::string strFile)
+bool CDB::PeriodicFlush(CWalletDBWrapper& dbw)
 {
+    if (dbw.IsDummy()) {
+        return true;
+    }
     bool ret = false;
+    CDBEnv *env = dbw.env;
+    const std::string& strFile = dbw.strFile;
     TRY_LOCK(bitdb.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 = bitdb.mapFileUseCount.begin();
-        while (mit != bitdb.mapFileUseCount.end())
+        std::map<std::string, int>::iterator mit = env->mapFileUseCount.begin();
+        while (mit != env->mapFileUseCount.end())
         {
             nRefCount += (*mit).second;
             mit++;
@@ -614,17 +627,17 @@ bool CDB::PeriodicFlush(std::string strFile)
         if (nRefCount == 0)
         {
             boost::this_thread::interruption_point();
-            std::map<std::string, int>::iterator mi = bitdb.mapFileUseCount.find(strFile);
-            if (mi != bitdb.mapFileUseCount.end())
+            std::map<std::string, int>::iterator mi = env->mapFileUseCount.find(strFile);
+            if (mi != env->mapFileUseCount.end())
             {
                 LogPrint(BCLog::DB, "Flushing %s\n", strFile);
                 int64_t nStart = GetTimeMillis();
 
                 // Flush wallet file so it's self contained
-                bitdb.CloseDb(strFile);
-                bitdb.CheckpointLSN(strFile);
+                env->CloseDb(strFile);
+                env->CheckpointLSN(strFile);
 
-                bitdb.mapFileUseCount.erase(mi++);
+                env->mapFileUseCount.erase(mi++);
                 LogPrint(BCLog::DB, "Flushed %s %dms\n", strFile, GetTimeMillis() - nStart);
                 ret = true;
             }
@@ -633,3 +646,52 @@ bool CDB::PeriodicFlush(std::string strFile)
 
     return ret;
 }
+
+bool CWalletDBWrapper::Rewrite(const char* pszSkip)
+{
+    return CDB::Rewrite(*this, pszSkip);
+}
+
+bool CWalletDBWrapper::Backup(const std::string& strDest)
+{
+    if (IsDummy()) {
+        return false;
+    }
+    while (true)
+    {
+        {
+            LOCK(env->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 = GetDataDir() / strFile;
+                fs::path pathDest(strDest);
+                if (fs::is_directory(pathDest))
+                    pathDest /= strFile;
+
+                try {
+                    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(), e.what());
+                    return false;
+                }
+            }
+        }
+        MilliSleep(100);
+    }
+    return false;
+}
+
+void CWalletDBWrapper::Flush(bool shutdown)
+{
+    if (!IsDummy()) {
+        env->Flush(shutdown);
+    }
+}
diff --git a/src/wallet/db.h b/src/wallet/db.h
index 9f912f9a1a..a0719820ac 100644
--- a/src/wallet/db.h
+++ b/src/wallet/db.h
@@ -86,6 +86,52 @@ public:
 
 extern CDBEnv bitdb;
 
+/** An instance of this class represents one database.
+ * For BerkeleyDB this is just a (env, strFile) tuple.
+ **/
+class CWalletDBWrapper
+{
+    friend class CDB;
+public:
+    /** Create dummy DB handle */
+    CWalletDBWrapper(): env(nullptr)
+    {
+    }
+
+    /** Create DB handle to real database */
+    CWalletDBWrapper(CDBEnv *env_in, const std::string &strFile_in):
+        env(env_in), strFile(strFile_in)
+    {
+    }
+
+    /** 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);
+
+    /** Get a name for this database, for debugging etc.
+     */
+    std::string GetName() const { return strFile; }
+
+    /** Make sure all changes are flushed to disk.
+     */
+    void Flush(bool shutdown);
+
+private:
+    /** BerkeleyDB specific */
+    CDBEnv *env;
+    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() { return env == nullptr; }
+};
+
 
 /** RAII class that provides access to a Berkeley database */
 class CDB
@@ -96,18 +142,19 @@ protected:
     DbTxn* activeTxn;
     bool fReadOnly;
     bool fFlushOnClose;
+    CDBEnv *env;
 
-    explicit CDB(const std::string& strFilename, const char* pszMode = "r+", bool fFlushOnCloseIn=true);
+public:
+    explicit CDB(CWalletDBWrapper& dbw, const char* pszMode = "r+", bool fFlushOnCloseIn=true);
     ~CDB() { Close(); }
 
-public:
     void Flush();
     void Close();
     static bool Recover(const std::string& filename, void *callbackDataIn, bool (*recoverKVcallback)(void* callbackData, CDataStream ssKey, CDataStream ssValue));
 
     /* flush the wallet passively (TRY_LOCK)
        ideal to be called periodically */
-    static bool PeriodicFlush(std::string strFile);
+    static bool PeriodicFlush(CWalletDBWrapper& dbw);
     /* verifies the database environment */
     static bool VerifyEnvironment(const std::string& walletFile, const fs::path& dataDir, std::string& errorStr);
     /* verifies the database file */
@@ -117,7 +164,7 @@ private:
     CDB(const CDB&);
     void operator=(const CDB&);
 
-protected:
+public:
     template <typename K, typename T>
     bool Read(const K& key, T& value)
     {
@@ -156,7 +203,7 @@ protected:
     bool Write(const K& key, const T& value, bool fOverwrite = true)
     {
         if (!pdb)
-            return false;
+            return true;
         if (fReadOnly)
             assert(!"Write called on database in read-only mode");
 
@@ -310,7 +357,7 @@ public:
         return Write(std::string("version"), nVersion);
     }
 
-    bool static Rewrite(const std::string& strFile, const char* pszSkip = NULL);
+    bool static Rewrite(CWalletDBWrapper& dbw, const char* pszSkip = NULL);
 };
 
 #endif // BITCOIN_WALLET_DB_H
diff --git a/src/wallet/rpcwallet.cpp b/src/wallet/rpcwallet.cpp
index 5cbeeab4eb..f8006a6255 100644
--- a/src/wallet/rpcwallet.cpp
+++ b/src/wallet/rpcwallet.cpp
@@ -2078,7 +2078,7 @@ UniValue walletpassphrase(const JSONRPCRequest& request)
 
     int64_t nSleepTime = request.params[1].get_int64();
     pwallet->nRelockTime = GetTime() + nSleepTime;
-    RPCRunLater(strprintf("lockwallet(%s)", pwallet->strWalletFile), boost::bind(LockWallet, pwallet), nSleepTime);
+    RPCRunLater(strprintf("lockwallet(%s)", pwallet->GetName()), boost::bind(LockWallet, pwallet), nSleepTime);
 
     return NullUniValue;
 }
diff --git a/src/wallet/test/wallet_test_fixture.cpp b/src/wallet/test/wallet_test_fixture.cpp
index a76db37617..1989bf8d9b 100644
--- a/src/wallet/test/wallet_test_fixture.cpp
+++ b/src/wallet/test/wallet_test_fixture.cpp
@@ -14,7 +14,8 @@ WalletTestingSetup::WalletTestingSetup(const std::string& chainName):
     bitdb.MakeMock();
 
     bool fFirstRun;
-    pwalletMain = new CWallet("wallet_test.dat");
+    std::unique_ptr<CWalletDBWrapper> dbw(new CWalletDBWrapper(&bitdb, "wallet_test.dat"));
+    pwalletMain = new CWallet(std::move(dbw));
     pwalletMain->LoadWallet(fFirstRun);
     RegisterValidationInterface(pwalletMain);
 
diff --git a/src/wallet/wallet.cpp b/src/wallet/wallet.cpp
index a8f07aba0d..211be76c45 100644
--- a/src/wallet/wallet.cpp
+++ b/src/wallet/wallet.cpp
@@ -162,7 +162,7 @@ void CWallet::DeriveNewChildKey(CKeyMetadata& metadata, CKey& secret, bool inter
     secret = childKey.key;
     metadata.hdMasterKeyID = hdChain.masterKeyID;
     // update the chain model in the database
-    if (!CWalletDB(strWalletFile).WriteHDChain(hdChain))
+    if (!CWalletDB(*dbw).WriteHDChain(hdChain))
         throw std::runtime_error(std::string(__func__) + ": Writing HD chain model failed");
 }
 
@@ -181,10 +181,8 @@ bool CWallet::AddKeyPubKey(const CKey& secret, const CPubKey &pubkey)
     if (HaveWatchOnly(script))
         RemoveWatchOnly(script);
 
-    if (!fFileBacked)
-        return true;
     if (!IsCrypted()) {
-        return CWalletDB(strWalletFile).WriteKey(pubkey,
+        return CWalletDB(*dbw).WriteKey(pubkey,
                                                  secret.GetPrivKey(),
                                                  mapKeyMetadata[pubkey.GetID()]);
     }
@@ -196,8 +194,6 @@ bool CWallet::AddCryptedKey(const CPubKey &vchPubKey,
 {
     if (!CCryptoKeyStore::AddCryptedKey(vchPubKey, vchCryptedSecret))
         return false;
-    if (!fFileBacked)
-        return true;
     {
         LOCK(cs_wallet);
         if (pwalletdbEncryption)
@@ -205,7 +201,7 @@ bool CWallet::AddCryptedKey(const CPubKey &vchPubKey,
                                                         vchCryptedSecret,
                                                         mapKeyMetadata[vchPubKey.GetID()]);
         else
-            return CWalletDB(strWalletFile).WriteCryptedKey(vchPubKey,
+            return CWalletDB(*dbw).WriteCryptedKey(vchPubKey,
                                                             vchCryptedSecret,
                                                             mapKeyMetadata[vchPubKey.GetID()]);
     }
@@ -241,9 +237,7 @@ bool CWallet::AddCScript(const CScript& redeemScript)
 {
     if (!CCryptoKeyStore::AddCScript(redeemScript))
         return false;
-    if (!fFileBacked)
-        return true;
-    return CWalletDB(strWalletFile).WriteCScript(Hash160(redeemScript), redeemScript);
+    return CWalletDB(*dbw).WriteCScript(Hash160(redeemScript), redeemScript);
 }
 
 bool CWallet::LoadCScript(const CScript& redeemScript)
@@ -269,9 +263,7 @@ bool CWallet::AddWatchOnly(const CScript& dest)
     const CKeyMetadata& meta = mapKeyMetadata[CScriptID(dest)];
     UpdateTimeFirstKey(meta.nCreateTime);
     NotifyWatchonlyChanged(true);
-    if (!fFileBacked)
-        return true;
-    return CWalletDB(strWalletFile).WriteWatchOnly(dest, meta);
+    return CWalletDB(*dbw).WriteWatchOnly(dest, meta);
 }
 
 bool CWallet::AddWatchOnly(const CScript& dest, int64_t nCreateTime)
@@ -287,9 +279,8 @@ bool CWallet::RemoveWatchOnly(const CScript &dest)
         return false;
     if (!HaveWatchOnly())
         NotifyWatchonlyChanged(false);
-    if (fFileBacked)
-        if (!CWalletDB(strWalletFile).EraseWatchOnly(dest))
-            return false;
+    if (!CWalletDB(*dbw).EraseWatchOnly(dest))
+        return false;
 
     return true;
 }
@@ -354,7 +345,7 @@ bool CWallet::ChangeWalletPassphrase(const SecureString& strOldWalletPassphrase,
                     return false;
                 if (!crypter.Encrypt(_vMasterKey, pMasterKey.second.vchCryptedKey))
                     return false;
-                CWalletDB(strWalletFile).WriteMasterKey(pMasterKey.first, pMasterKey.second);
+                CWalletDB(*dbw).WriteMasterKey(pMasterKey.first, pMasterKey.second);
                 if (fWasLocked)
                     Lock();
                 return true;
@@ -367,7 +358,7 @@ bool CWallet::ChangeWalletPassphrase(const SecureString& strOldWalletPassphrase,
 
 void CWallet::SetBestChain(const CBlockLocator& loc)
 {
-    CWalletDB walletdb(strWalletFile);
+    CWalletDB walletdb(*dbw);
     walletdb.WriteBestBlock(loc);
 }
 
@@ -386,9 +377,8 @@ bool CWallet::SetMinVersion(enum WalletFeature nVersion, CWalletDB* pwalletdbIn,
     if (nVersion > nWalletMaxVersion)
         nWalletMaxVersion = nVersion;
 
-    if (fFileBacked)
     {
-        CWalletDB* pwalletdb = pwalletdbIn ? pwalletdbIn : new CWalletDB(strWalletFile);
+        CWalletDB* pwalletdb = pwalletdbIn ? pwalletdbIn : new CWalletDB(*dbw);
         if (nWalletVersion > 40000)
             pwalletdb->WriteMinVersion(nWalletVersion);
         if (!pwalletdbIn)
@@ -442,7 +432,7 @@ bool CWallet::HasWalletSpend(const uint256& txid) const
 
 void CWallet::Flush(bool shutdown)
 {
-    bitdb.Flush(shutdown);
+    dbw->Flush(shutdown);
 }
 
 bool CWallet::Verify()
@@ -595,24 +585,19 @@ bool CWallet::EncryptWallet(const SecureString& strWalletPassphrase)
     {
         LOCK(cs_wallet);
         mapMasterKeys[++nMasterKeyMaxID] = kMasterKey;
-        if (fFileBacked)
-        {
-            assert(!pwalletdbEncryption);
-            pwalletdbEncryption = new CWalletDB(strWalletFile);
-            if (!pwalletdbEncryption->TxnBegin()) {
-                delete pwalletdbEncryption;
-                pwalletdbEncryption = NULL;
-                return false;
-            }
-            pwalletdbEncryption->WriteMasterKey(nMasterKeyMaxID, kMasterKey);
+        assert(!pwalletdbEncryption);
+        pwalletdbEncryption = new CWalletDB(*dbw);
+        if (!pwalletdbEncryption->TxnBegin()) {
+            delete pwalletdbEncryption;
+            pwalletdbEncryption = NULL;
+            return false;
         }
+        pwalletdbEncryption->WriteMasterKey(nMasterKeyMaxID, kMasterKey);
 
         if (!EncryptKeys(_vMasterKey))
         {
-            if (fFileBacked) {
-                pwalletdbEncryption->TxnAbort();
-                delete pwalletdbEncryption;
-            }
+            pwalletdbEncryption->TxnAbort();
+            delete pwalletdbEncryption;
             // We now probably have half of our keys encrypted in memory, and half not...
             // die and let the user reload the unencrypted wallet.
             assert(false);
@@ -621,19 +606,16 @@ bool CWallet::EncryptWallet(const SecureString& strWalletPassphrase)
         // Encryption was introduced in version 0.4.0
         SetMinVersion(FEATURE_WALLETCRYPT, pwalletdbEncryption, true);
 
-        if (fFileBacked)
-        {
-            if (!pwalletdbEncryption->TxnCommit()) {
-                delete pwalletdbEncryption;
-                // We now have keys encrypted in memory, but not on disk...
-                // die to avoid confusion and let the user reload the unencrypted wallet.
-                assert(false);
-            }
-
+        if (!pwalletdbEncryption->TxnCommit()) {
             delete pwalletdbEncryption;
-            pwalletdbEncryption = NULL;
+            // We now have keys encrypted in memory, but not on disk...
+            // die to avoid confusion and let the user reload the unencrypted wallet.
+            assert(false);
         }
 
+        delete pwalletdbEncryption;
+        pwalletdbEncryption = NULL;
+
         Lock();
         Unlock(strWalletPassphrase);
 
@@ -652,7 +634,7 @@ bool CWallet::EncryptWallet(const SecureString& strWalletPassphrase)
 
         // Need to completely rewrite the wallet file; if we don't, bdb might keep
         // bits of the unencrypted private key in slack space in the database file.
-        CDB::Rewrite(strWalletFile);
+        dbw->Rewrite();
 
     }
     NotifyStatusChanged(this);
@@ -663,7 +645,7 @@ bool CWallet::EncryptWallet(const SecureString& strWalletPassphrase)
 DBErrors CWallet::ReorderTransactions()
 {
     LOCK(cs_wallet);
-    CWalletDB walletdb(strWalletFile);
+    CWalletDB walletdb(*dbw);
 
     // Old wallets didn't have any defined order for transactions
     // Probably a bad idea to change the output of this
@@ -744,14 +726,14 @@ int64_t CWallet::IncOrderPosNext(CWalletDB *pwalletdb)
     if (pwalletdb) {
         pwalletdb->WriteOrderPosNext(nOrderPosNext);
     } else {
-        CWalletDB(strWalletFile).WriteOrderPosNext(nOrderPosNext);
+        CWalletDB(*dbw).WriteOrderPosNext(nOrderPosNext);
     }
     return nRet;
 }
 
 bool CWallet::AccountMove(std::string strFrom, std::string strTo, CAmount nAmount, std::string strComment)
 {
-    CWalletDB walletdb(strWalletFile);
+    CWalletDB walletdb(*dbw);
     if (!walletdb.TxnBegin())
         return false;
 
@@ -785,7 +767,7 @@ bool CWallet::AccountMove(std::string strFrom, std::string strTo, CAmount nAmoun
 
 bool CWallet::GetAccountPubkey(CPubKey &pubKey, std::string strAccount, bool bForceNew)
 {
-    CWalletDB walletdb(strWalletFile);
+    CWalletDB walletdb(*dbw);
 
     CAccount account;
     walletdb.ReadAccount(strAccount, account);
@@ -846,7 +828,7 @@ bool CWallet::MarkReplaced(const uint256& originalHash, const uint256& newHash)
 
     wtx.mapValue["replaced_by_txid"] = newHash.ToString();
 
-    CWalletDB walletdb(strWalletFile, "r+");
+    CWalletDB walletdb(*dbw, "r+");
 
     bool success = true;
     if (!walletdb.WriteTx(wtx)) {
@@ -863,7 +845,7 @@ bool CWallet::AddToWallet(const CWalletTx& wtxIn, bool fFlushOnClose)
 {
     LOCK(cs_wallet);
 
-    CWalletDB walletdb(strWalletFile, "r+", fFlushOnClose);
+    CWalletDB walletdb(*dbw, "r+", fFlushOnClose);
 
     uint256 hash = wtxIn.GetHash();
 
@@ -1007,7 +989,7 @@ bool CWallet::AbandonTransaction(const uint256& hashTx)
 {
     LOCK2(cs_main, cs_wallet);
 
-    CWalletDB walletdb(strWalletFile, "r+");
+    CWalletDB walletdb(*dbw, "r+");
 
     std::set<uint256> todo;
     std::set<uint256> done;
@@ -1079,7 +1061,7 @@ void CWallet::MarkConflicted(const uint256& hashBlock, const uint256& hashTx)
         return;
 
     // Do not flush the wallet here for performance reasons
-    CWalletDB walletdb(strWalletFile, "r+", false);
+    CWalletDB walletdb(*dbw, "r+", false);
 
     std::set<uint256> todo;
     std::set<uint256> done;
@@ -1362,7 +1344,7 @@ bool CWallet::SetHDMasterKey(const CPubKey& pubkey, CHDChain *possibleOldChain)
 bool CWallet::SetHDChain(const CHDChain& chain, bool memonly)
 {
     LOCK(cs_wallet);
-    if (!memonly && !CWalletDB(strWalletFile).WriteHDChain(chain))
+    if (!memonly && !CWalletDB(*dbw).WriteHDChain(chain))
         throw std::runtime_error(std::string(__func__) + ": writing chain failed");
 
     hdChain = chain;
@@ -2759,13 +2741,13 @@ bool CWallet::CommitTransaction(CWalletTx& wtxNew, CReserveKey& reservekey, CCon
 }
 
 void CWallet::ListAccountCreditDebit(const std::string& strAccount, std::list<CAccountingEntry>& entries) {
-    CWalletDB walletdb(strWalletFile);
+    CWalletDB walletdb(*dbw);
     return walletdb.ListAccountCreditDebit(strAccount, entries);
 }
 
 bool CWallet::AddAccountingEntry(const CAccountingEntry& acentry)
 {
-    CWalletDB walletdb(strWalletFile);
+    CWalletDB walletdb(*dbw);
 
     return AddAccountingEntry(acentry, &walletdb);
 }
@@ -2817,13 +2799,11 @@ CAmount CWallet::GetMinimumFee(unsigned int nTxBytes, unsigned int nConfirmTarge
 
 DBErrors CWallet::LoadWallet(bool& fFirstRunRet)
 {
-    if (!fFileBacked)
-        return DB_LOAD_OK;
     fFirstRunRet = false;
-    DBErrors nLoadWalletRet = CWalletDB(strWalletFile,"cr+").LoadWallet(this);
+    DBErrors nLoadWalletRet = CWalletDB(*dbw,"cr+").LoadWallet(this);
     if (nLoadWalletRet == DB_NEED_REWRITE)
     {
-        if (CDB::Rewrite(strWalletFile, "\x04pool"))
+        if (dbw->Rewrite("\x04pool"))
         {
             LOCK(cs_wallet);
             setKeyPool.clear();
@@ -2844,17 +2824,15 @@ DBErrors CWallet::LoadWallet(bool& fFirstRunRet)
 
 DBErrors CWallet::ZapSelectTx(std::vector<uint256>& vHashIn, std::vector<uint256>& vHashOut)
 {
-    if (!fFileBacked)
-        return DB_LOAD_OK;
     AssertLockHeld(cs_wallet); // mapWallet
     vchDefaultKey = CPubKey();
-    DBErrors nZapSelectTxRet = CWalletDB(strWalletFile,"cr+").ZapSelectTx(vHashIn, vHashOut);
+    DBErrors nZapSelectTxRet = CWalletDB(*dbw,"cr+").ZapSelectTx(vHashIn, vHashOut);
     for (uint256 hash : vHashOut)
         mapWallet.erase(hash);
 
     if (nZapSelectTxRet == DB_NEED_REWRITE)
     {
-        if (CDB::Rewrite(strWalletFile, "\x04pool"))
+        if (dbw->Rewrite("\x04pool"))
         {
             setKeyPool.clear();
             // Note: can't top-up keypool here, because wallet is locked.
@@ -2874,13 +2852,11 @@ DBErrors CWallet::ZapSelectTx(std::vector<uint256>& vHashIn, std::vector<uint256
 
 DBErrors CWallet::ZapWalletTx(std::vector<CWalletTx>& vWtx)
 {
-    if (!fFileBacked)
-        return DB_LOAD_OK;
     vchDefaultKey = CPubKey();
-    DBErrors nZapWalletTxRet = CWalletDB(strWalletFile,"cr+").ZapWalletTx(vWtx);
+    DBErrors nZapWalletTxRet = CWalletDB(*dbw,"cr+").ZapWalletTx(vWtx);
     if (nZapWalletTxRet == DB_NEED_REWRITE)
     {
-        if (CDB::Rewrite(strWalletFile, "\x04pool"))
+        if (dbw->Rewrite("\x04pool"))
         {
             LOCK(cs_wallet);
             setKeyPool.clear();
@@ -2910,11 +2886,9 @@ bool CWallet::SetAddressBook(const CTxDestination& address, const std::string& s
     }
     NotifyAddressBookChanged(this, address, strName, ::IsMine(*this, address) != ISMINE_NO,
                              strPurpose, (fUpdated ? CT_UPDATED : CT_NEW) );
-    if (!fFileBacked)
-        return false;
-    if (!strPurpose.empty() && !CWalletDB(strWalletFile).WritePurpose(CBitcoinAddress(address).ToString(), strPurpose))
+    if (!strPurpose.empty() && !CWalletDB(*dbw).WritePurpose(CBitcoinAddress(address).ToString(), strPurpose))
         return false;
-    return CWalletDB(strWalletFile).WriteName(CBitcoinAddress(address).ToString(), strName);
+    return CWalletDB(*dbw).WriteName(CBitcoinAddress(address).ToString(), strName);
 }
 
 bool CWallet::DelAddressBook(const CTxDestination& address)
@@ -2922,33 +2896,25 @@ bool CWallet::DelAddressBook(const CTxDestination& address)
     {
         LOCK(cs_wallet); // mapAddressBook
 
-        if(fFileBacked)
+        // Delete destdata tuples associated with address
+        std::string strAddress = CBitcoinAddress(address).ToString();
+        BOOST_FOREACH(const PAIRTYPE(std::string, std::string) &item, mapAddressBook[address].destdata)
         {
-            // Delete destdata tuples associated with address
-            std::string strAddress = CBitcoinAddress(address).ToString();
-            BOOST_FOREACH(const PAIRTYPE(std::string, std::string) &item, mapAddressBook[address].destdata)
-            {
-                CWalletDB(strWalletFile).EraseDestData(strAddress, item.first);
-            }
+            CWalletDB(*dbw).EraseDestData(strAddress, item.first);
         }
         mapAddressBook.erase(address);
     }
 
     NotifyAddressBookChanged(this, address, "", ::IsMine(*this, address) != ISMINE_NO, "", CT_DELETED);
 
-    if (!fFileBacked)
-        return false;
-    CWalletDB(strWalletFile).ErasePurpose(CBitcoinAddress(address).ToString());
-    return CWalletDB(strWalletFile).EraseName(CBitcoinAddress(address).ToString());
+    CWalletDB(*dbw).ErasePurpose(CBitcoinAddress(address).ToString());
+    return CWalletDB(*dbw).EraseName(CBitcoinAddress(address).ToString());
 }
 
 bool CWallet::SetDefaultKey(const CPubKey &vchPubKey)
 {
-    if (fFileBacked)
-    {
-        if (!CWalletDB(strWalletFile).WriteDefaultKey(vchPubKey))
-            return false;
-    }
+    if (!CWalletDB(*dbw).WriteDefaultKey(vchPubKey))
+        return false;
     vchDefaultKey = vchPubKey;
     return true;
 }
@@ -2961,7 +2927,7 @@ bool CWallet::NewKeyPool()
 {
     {
         LOCK(cs_wallet);
-        CWalletDB walletdb(strWalletFile);
+        CWalletDB walletdb(*dbw);
         BOOST_FOREACH(int64_t nIndex, setKeyPool)
             walletdb.ErasePool(nIndex);
         setKeyPool.clear();
@@ -2982,7 +2948,7 @@ size_t CWallet::KeypoolCountExternalKeys()
     if (!IsHDEnabled() || !CanSupportFeature(FEATURE_HD_SPLIT))
         return setKeyPool.size();
 
-    CWalletDB walletdb(strWalletFile);
+    CWalletDB walletdb(*dbw);
 
     // count amount of external keys
     size_t amountE = 0;
@@ -3025,7 +2991,7 @@ bool CWallet::TopUpKeyPool(unsigned int kpSize)
             missingInternal = 0;
         }
         bool internal = false;
-        CWalletDB walletdb(strWalletFile);
+        CWalletDB walletdb(*dbw);
         for (int64_t i = missingInternal + missingExternal; i--;)
         {
             int64_t nEnd = 1;
@@ -3056,7 +3022,7 @@ void CWallet::ReserveKeyFromKeyPool(int64_t& nIndex, CKeyPool& keypool, bool int
         if(setKeyPool.empty())
             return;
 
-        CWalletDB walletdb(strWalletFile);
+        CWalletDB walletdb(*dbw);
 
         // try to find a key that matches the internal/external filter
         for(const int64_t& id : setKeyPool)
@@ -3082,11 +3048,8 @@ void CWallet::ReserveKeyFromKeyPool(int64_t& nIndex, CKeyPool& keypool, bool int
 void CWallet::KeepKey(int64_t nIndex)
 {
     // Remove from key pool
-    if (fFileBacked)
-    {
-        CWalletDB walletdb(strWalletFile);
-        walletdb.ErasePool(nIndex);
-    }
+    CWalletDB walletdb(*dbw);
+    walletdb.ErasePool(nIndex);
     LogPrintf("keypool keep %d\n", nIndex);
 }
 
@@ -3128,7 +3091,7 @@ int64_t CWallet::GetOldestKeyPoolTime()
         return GetTime();
 
     CKeyPool keypool;
-    CWalletDB walletdb(strWalletFile);
+    CWalletDB walletdb(*dbw);
 
     if (IsHDEnabled() && CanSupportFeature(FEATURE_HD_SPLIT))
     {
@@ -3296,7 +3259,7 @@ std::set< std::set<CTxDestination> > CWallet::GetAddressGroupings()
 
 CAmount CWallet::GetAccountBalance(const std::string& strAccount, int nMinDepth, const isminefilter& filter)
 {
-    CWalletDB walletdb(strWalletFile);
+    CWalletDB walletdb(*dbw);
     return GetAccountBalance(walletdb, strAccount, nMinDepth, filter);
 }
 
@@ -3376,7 +3339,7 @@ void CWallet::GetAllReserveKeys(std::set<CKeyID>& setAddress) const
 {
     setAddress.clear();
 
-    CWalletDB walletdb(strWalletFile);
+    CWalletDB walletdb(*dbw);
 
     LOCK2(cs_main, cs_wallet);
     BOOST_FOREACH(const int64_t& id, setKeyPool)
@@ -3598,18 +3561,14 @@ bool CWallet::AddDestData(const CTxDestination &dest, const std::string &key, co
         return false;
 
     mapAddressBook[dest].destdata.insert(std::make_pair(key, value));
-    if (!fFileBacked)
-        return true;
-    return CWalletDB(strWalletFile).WriteDestData(CBitcoinAddress(dest).ToString(), key, value);
+    return CWalletDB(*dbw).WriteDestData(CBitcoinAddress(dest).ToString(), key, value);
 }
 
 bool CWallet::EraseDestData(const CTxDestination &dest, const std::string &key)
 {
     if (!mapAddressBook[dest].destdata.erase(key))
         return false;
-    if (!fFileBacked)
-        return true;
-    return CWalletDB(strWalletFile).EraseDestData(CBitcoinAddress(dest).ToString(), key);
+    return CWalletDB(*dbw).EraseDestData(CBitcoinAddress(dest).ToString(), key);
 }
 
 bool CWallet::LoadDestData(const CTxDestination &dest, const std::string &key, const std::string &value)
@@ -3679,7 +3638,8 @@ CWallet* CWallet::CreateWalletFromFile(const std::string walletFile)
     if (GetBoolArg("-zapwallettxes", false)) {
         uiInterface.InitMessage(_("Zapping all transactions from wallet..."));
 
-        CWallet *tempWallet = new CWallet(walletFile);
+        std::unique_ptr<CWalletDBWrapper> dbw(new CWalletDBWrapper(&bitdb, walletFile));
+        CWallet *tempWallet = new CWallet(std::move(dbw));
         DBErrors nZapWalletRet = tempWallet->ZapWalletTx(vWtx);
         if (nZapWalletRet != DB_LOAD_OK) {
             InitError(strprintf(_("Error loading %s: Wallet corrupted"), walletFile));
@@ -3694,7 +3654,8 @@ CWallet* CWallet::CreateWalletFromFile(const std::string walletFile)
 
     int64_t nStart = GetTimeMillis();
     bool fFirstRun = true;
-    CWallet *walletInstance = new CWallet(walletFile);
+    std::unique_ptr<CWalletDBWrapper> dbw(new CWalletDBWrapper(&bitdb, walletFile));
+    CWallet *walletInstance = new CWallet(std::move(dbw));
     DBErrors nLoadWalletRet = walletInstance->LoadWallet(fFirstRun);
     if (nLoadWalletRet != DB_LOAD_OK)
     {
@@ -3785,7 +3746,7 @@ CWallet* CWallet::CreateWalletFromFile(const std::string walletFile)
     CBlockIndex *pindexRescan = chainActive.Genesis();
     if (!GetBoolArg("-rescan", false))
     {
-        CWalletDB walletdb(walletFile);
+        CWalletDB walletdb(*walletInstance->dbw);
         CBlockLocator locator;
         if (walletdb.ReadBestBlock(locator))
             pindexRescan = FindForkInGlobalIndex(chainActive, locator);
@@ -3818,7 +3779,7 @@ CWallet* CWallet::CreateWalletFromFile(const std::string walletFile)
         // Restore wallet transaction metadata after -zapwallettxes=1
         if (GetBoolArg("-zapwallettxes", false) && GetArg("-zapwallettxes", "1") != "2")
         {
-            CWalletDB walletdb(walletFile);
+            CWalletDB walletdb(*walletInstance->dbw);
 
             BOOST_FOREACH(const CWalletTx& wtxOld, vWtx)
             {
@@ -3978,38 +3939,7 @@ bool CWallet::ParameterInteraction()
 
 bool CWallet::BackupWallet(const std::string& strDest)
 {
-    if (!fFileBacked)
-        return false;
-    while (true)
-    {
-        {
-            LOCK(bitdb.cs_db);
-            if (!bitdb.mapFileUseCount.count(strWalletFile) || bitdb.mapFileUseCount[strWalletFile] == 0)
-            {
-                // Flush log data to the dat file
-                bitdb.CloseDb(strWalletFile);
-                bitdb.CheckpointLSN(strWalletFile);
-                bitdb.mapFileUseCount.erase(strWalletFile);
-
-                // Copy wallet file
-                fs::path pathSrc = GetDataDir() / strWalletFile;
-                fs::path pathDest(strDest);
-                if (fs::is_directory(pathDest))
-                    pathDest /= strWalletFile;
-
-                try {
-                    fs::copy_file(pathSrc, pathDest, fs::copy_option::overwrite_if_exists);
-                    LogPrintf("copied %s to %s\n", strWalletFile, pathDest.string());
-                    return true;
-                } catch (const fs::filesystem_error& e) {
-                    LogPrintf("error copying %s to %s - %s\n", strWalletFile, pathDest.string(), e.what());
-                    return false;
-                }
-            }
-        }
-        MilliSleep(100);
-    }
-    return false;
+    return dbw->Backup(strDest);
 }
 
 CKeyPool::CKeyPool()
diff --git a/src/wallet/wallet.h b/src/wallet/wallet.h
index c0ed44377f..a52ae99ed1 100644
--- a/src/wallet/wallet.h
+++ b/src/wallet/wallet.h
@@ -699,8 +699,6 @@ private:
     /* HD derive new child key (on internal or external chain) */
     void DeriveNewChildKey(CKeyMetadata& metadata, CKey& secret, bool internal = false);
 
-    bool fFileBacked;
-
     std::set<int64_t> setKeyPool;
 
     int64_t nTimeFirstKey;
@@ -716,17 +714,33 @@ private:
      */
     bool AddWatchOnly(const CScript& dest) override;
 
+    std::unique_ptr<CWalletDBWrapper> dbw;
+
 public:
     /*
      * Main wallet lock.
-     * This lock protects all the fields added by CWallet
-     *   except for:
-     *      fFileBacked (immutable after instantiation)
-     *      strWalletFile (immutable after instantiation)
+     * This lock protects all the fields added by CWallet.
      */
     mutable CCriticalSection cs_wallet;
 
-    const std::string strWalletFile;
+    /** Get database handle used by this wallet. Ideally this function would
+     * not be necessary.
+     */
+    CWalletDBWrapper& GetDBHandle()
+    {
+        return *dbw;
+    }
+
+    /** Get a name for this wallet for logging/debugging purposes.
+     */
+    std::string GetName() const
+    {
+        if (dbw) {
+            return dbw->GetName();
+        } else {
+            return "dummy";
+        }
+    }
 
     void LoadKeyPool(int nIndex, const CKeyPool &keypool)
     {
@@ -748,15 +762,16 @@ public:
     MasterKeyMap mapMasterKeys;
     unsigned int nMasterKeyMaxID;
 
-    CWallet()
+    // Create wallet with dummy database handle
+    CWallet(): dbw(new CWalletDBWrapper())
     {
         SetNull();
     }
 
-    CWallet(const std::string& strWalletFileIn) : strWalletFile(strWalletFileIn)
+    // Create wallet with passed-in database handle
+    CWallet(std::unique_ptr<CWalletDBWrapper> dbw_in) : dbw(std::move(dbw_in))
     {
         SetNull();
-        fFileBacked = true;
     }
 
     ~CWallet()
@@ -769,7 +784,6 @@ public:
     {
         nWalletVersion = FEATURE_BASE;
         nWalletMaxVersion = FEATURE_BASE;
-        fFileBacked = false;
         nMasterKeyMaxID = 0;
         pwalletdbEncryption = NULL;
         nOrderPosNext = 0;
diff --git a/src/wallet/walletdb.cpp b/src/wallet/walletdb.cpp
index ceff2d36e3..a90fa6dbbd 100644
--- a/src/wallet/walletdb.cpp
+++ b/src/wallet/walletdb.cpp
@@ -33,7 +33,7 @@ static std::atomic<unsigned int> nWalletDBUpdateCounter;
 bool CWalletDB::WriteName(const std::string& strAddress, const std::string& strName)
 {
     nWalletDBUpdateCounter++;
-    return Write(make_pair(std::string("name"), strAddress), strName);
+    return batch.Write(std::make_pair(std::string("name"), strAddress), strName);
 }
 
 bool CWalletDB::EraseName(const std::string& strAddress)
@@ -41,38 +41,38 @@ bool CWalletDB::EraseName(const std::string& strAddress)
     // This should only be used for sending addresses, never for receiving addresses,
     // receiving addresses must always have an address book entry if they're not change return.
     nWalletDBUpdateCounter++;
-    return Erase(make_pair(std::string("name"), strAddress));
+    return batch.Erase(std::make_pair(std::string("name"), strAddress));
 }
 
 bool CWalletDB::WritePurpose(const std::string& strAddress, const std::string& strPurpose)
 {
     nWalletDBUpdateCounter++;
-    return Write(make_pair(std::string("purpose"), strAddress), strPurpose);
+    return batch.Write(std::make_pair(std::string("purpose"), strAddress), strPurpose);
 }
 
 bool CWalletDB::ErasePurpose(const std::string& strPurpose)
 {
     nWalletDBUpdateCounter++;
-    return Erase(make_pair(std::string("purpose"), strPurpose));
+    return batch.Erase(std::make_pair(std::string("purpose"), strPurpose));
 }
 
 bool CWalletDB::WriteTx(const CWalletTx& wtx)
 {
     nWalletDBUpdateCounter++;
-    return Write(std::make_pair(std::string("tx"), wtx.GetHash()), wtx);
+    return batch.Write(std::make_pair(std::string("tx"), wtx.GetHash()), wtx);
 }
 
 bool CWalletDB::EraseTx(uint256 hash)
 {
     nWalletDBUpdateCounter++;
-    return Erase(std::make_pair(std::string("tx"), hash));
+    return batch.Erase(std::make_pair(std::string("tx"), hash));
 }
 
 bool CWalletDB::WriteKey(const CPubKey& vchPubKey, const CPrivKey& vchPrivKey, const CKeyMetadata& keyMeta)
 {
     nWalletDBUpdateCounter++;
 
-    if (!Write(std::make_pair(std::string("keymeta"), vchPubKey),
+    if (!batch.Write(std::make_pair(std::string("keymeta"), vchPubKey),
                keyMeta, false))
         return false;
 
@@ -82,7 +82,7 @@ bool CWalletDB::WriteKey(const CPubKey& vchPubKey, const CPrivKey& vchPrivKey, c
     vchKey.insert(vchKey.end(), vchPubKey.begin(), vchPubKey.end());
     vchKey.insert(vchKey.end(), vchPrivKey.begin(), vchPrivKey.end());
 
-    return Write(std::make_pair(std::string("key"), vchPubKey), std::make_pair(vchPrivKey, Hash(vchKey.begin(), vchKey.end())), false);
+    return batch.Write(std::make_pair(std::string("key"), vchPubKey), std::make_pair(vchPrivKey, Hash(vchKey.begin(), vchKey.end())), false);
 }
 
 bool CWalletDB::WriteCryptedKey(const CPubKey& vchPubKey,
@@ -92,16 +92,16 @@ bool CWalletDB::WriteCryptedKey(const CPubKey& vchPubKey,
     const bool fEraseUnencryptedKey = true;
     nWalletDBUpdateCounter++;
 
-    if (!Write(std::make_pair(std::string("keymeta"), vchPubKey),
+    if (!batch.Write(std::make_pair(std::string("keymeta"), vchPubKey),
             keyMeta))
         return false;
 
-    if (!Write(std::make_pair(std::string("ckey"), vchPubKey), vchCryptedSecret, false))
+    if (!batch.Write(std::make_pair(std::string("ckey"), vchPubKey), vchCryptedSecret, false))
         return false;
     if (fEraseUnencryptedKey)
     {
-        Erase(std::make_pair(std::string("key"), vchPubKey));
-        Erase(std::make_pair(std::string("wkey"), vchPubKey));
+        batch.Erase(std::make_pair(std::string("key"), vchPubKey));
+        batch.Erase(std::make_pair(std::string("wkey"), vchPubKey));
     }
     return true;
 }
@@ -109,92 +109,92 @@ bool CWalletDB::WriteCryptedKey(const CPubKey& vchPubKey,
 bool CWalletDB::WriteMasterKey(unsigned int nID, const CMasterKey& kMasterKey)
 {
     nWalletDBUpdateCounter++;
-    return Write(std::make_pair(std::string("mkey"), nID), kMasterKey, true);
+    return batch.Write(std::make_pair(std::string("mkey"), nID), kMasterKey, true);
 }
 
 bool CWalletDB::WriteCScript(const uint160& hash, const CScript& redeemScript)
 {
     nWalletDBUpdateCounter++;
-    return Write(std::make_pair(std::string("cscript"), hash), *(const CScriptBase*)(&redeemScript), false);
+    return batch.Write(std::make_pair(std::string("cscript"), hash), *(const CScriptBase*)(&redeemScript), false);
 }
 
 bool CWalletDB::WriteWatchOnly(const CScript &dest, const CKeyMetadata& keyMeta)
 {
     nWalletDBUpdateCounter++;
-    if (!Write(std::make_pair(std::string("watchmeta"), *(const CScriptBase*)(&dest)), keyMeta))
+    if (!batch.Write(std::make_pair(std::string("watchmeta"), *(const CScriptBase*)(&dest)), keyMeta))
         return false;
-    return Write(std::make_pair(std::string("watchs"), *(const CScriptBase*)(&dest)), '1');
+    return batch.Write(std::make_pair(std::string("watchs"), *(const CScriptBase*)(&dest)), '1');
 }
 
 bool CWalletDB::EraseWatchOnly(const CScript &dest)
 {
     nWalletDBUpdateCounter++;
-    if (!Erase(std::make_pair(std::string("watchmeta"), *(const CScriptBase*)(&dest))))
+    if (!batch.Erase(std::make_pair(std::string("watchmeta"), *(const CScriptBase*)(&dest))))
         return false;
-    return Erase(std::make_pair(std::string("watchs"), *(const CScriptBase*)(&dest)));
+    return batch.Erase(std::make_pair(std::string("watchs"), *(const CScriptBase*)(&dest)));
 }
 
 bool CWalletDB::WriteBestBlock(const CBlockLocator& locator)
 {
     nWalletDBUpdateCounter++;
-    Write(std::string("bestblock"), CBlockLocator()); // Write empty block locator so versions that require a merkle branch automatically rescan
-    return Write(std::string("bestblock_nomerkle"), locator);
+    batch.Write(std::string("bestblock"), CBlockLocator()); // Write empty block locator so versions that require a merkle branch automatically rescan
+    return batch.Write(std::string("bestblock_nomerkle"), locator);
 }
 
 bool CWalletDB::ReadBestBlock(CBlockLocator& locator)
 {
-    if (Read(std::string("bestblock"), locator) && !locator.vHave.empty()) return true;
-    return Read(std::string("bestblock_nomerkle"), locator);
+    if (batch.Read(std::string("bestblock"), locator) && !locator.vHave.empty()) return true;
+    return batch.Read(std::string("bestblock_nomerkle"), locator);
 }
 
 bool CWalletDB::WriteOrderPosNext(int64_t nOrderPosNext)
 {
     nWalletDBUpdateCounter++;
-    return Write(std::string("orderposnext"), nOrderPosNext);
+    return batch.Write(std::string("orderposnext"), nOrderPosNext);
 }
 
 bool CWalletDB::WriteDefaultKey(const CPubKey& vchPubKey)
 {
     nWalletDBUpdateCounter++;
-    return Write(std::string("defaultkey"), vchPubKey);
+    return batch.Write(std::string("defaultkey"), vchPubKey);
 }
 
 bool CWalletDB::ReadPool(int64_t nPool, CKeyPool& keypool)
 {
-    return Read(std::make_pair(std::string("pool"), nPool), keypool);
+    return batch.Read(std::make_pair(std::string("pool"), nPool), keypool);
 }
 
 bool CWalletDB::WritePool(int64_t nPool, const CKeyPool& keypool)
 {
     nWalletDBUpdateCounter++;
-    return Write(std::make_pair(std::string("pool"), nPool), keypool);
+    return batch.Write(std::make_pair(std::string("pool"), nPool), keypool);
 }
 
 bool CWalletDB::ErasePool(int64_t nPool)
 {
     nWalletDBUpdateCounter++;
-    return Erase(std::make_pair(std::string("pool"), nPool));
+    return batch.Erase(std::make_pair(std::string("pool"), nPool));
 }
 
 bool CWalletDB::WriteMinVersion(int nVersion)
 {
-    return Write(std::string("minversion"), nVersion);
+    return batch.Write(std::string("minversion"), nVersion);
 }
 
 bool CWalletDB::ReadAccount(const std::string& strAccount, CAccount& account)
 {
     account.SetNull();
-    return Read(make_pair(std::string("acc"), strAccount), account);
+    return batch.Read(std::make_pair(std::string("acc"), strAccount), account);
 }
 
 bool CWalletDB::WriteAccount(const std::string& strAccount, const CAccount& account)
 {
-    return Write(make_pair(std::string("acc"), strAccount), account);
+    return batch.Write(std::make_pair(std::string("acc"), strAccount), account);
 }
 
 bool CWalletDB::WriteAccountingEntry(const uint64_t nAccEntryNum, const CAccountingEntry& acentry)
 {
-    return Write(std::make_pair(std::string("acentry"), std::make_pair(acentry.strAccount, nAccEntryNum)), acentry);
+    return batch.Write(std::make_pair(std::string("acentry"), std::make_pair(acentry.strAccount, nAccEntryNum)), acentry);
 }
 
 bool CWalletDB::WriteAccountingEntry_Backend(const CAccountingEntry& acentry)
@@ -218,7 +218,7 @@ void CWalletDB::ListAccountCreditDebit(const std::string& strAccount, std::list<
 {
     bool fAllAccounts = (strAccount == "*");
 
-    Dbc* pcursor = GetCursor();
+    Dbc* pcursor = batch.GetCursor();
     if (!pcursor)
         throw std::runtime_error(std::string(__func__) + ": cannot create DB cursor");
     bool setRange = true;
@@ -229,7 +229,7 @@ void CWalletDB::ListAccountCreditDebit(const std::string& strAccount, std::list<
         if (setRange)
             ssKey << std::make_pair(std::string("acentry"), std::make_pair((fAllAccounts ? std::string("") : strAccount), uint64_t(0)));
         CDataStream ssValue(SER_DISK, CLIENT_VERSION);
-        int ret = ReadAtCursor(pcursor, ssKey, ssValue, setRange);
+        int ret = batch.ReadAtCursor(pcursor, ssKey, ssValue, setRange);
         setRange = false;
         if (ret == DB_NOTFOUND)
             break;
@@ -560,7 +560,7 @@ DBErrors CWalletDB::LoadWallet(CWallet* pwallet)
     LOCK(pwallet->cs_wallet);
     try {
         int nMinVersion = 0;
-        if (Read((std::string)"minversion", nMinVersion))
+        if (batch.Read((std::string)"minversion", nMinVersion))
         {
             if (nMinVersion > CLIENT_VERSION)
                 return DB_TOO_NEW;
@@ -568,7 +568,7 @@ DBErrors CWalletDB::LoadWallet(CWallet* pwallet)
         }
 
         // Get cursor
-        Dbc* pcursor = GetCursor();
+        Dbc* pcursor = batch.GetCursor();
         if (!pcursor)
         {
             LogPrintf("Error getting wallet database cursor\n");
@@ -580,7 +580,7 @@ DBErrors CWalletDB::LoadWallet(CWallet* pwallet)
             // Read next record
             CDataStream ssKey(SER_DISK, CLIENT_VERSION);
             CDataStream ssValue(SER_DISK, CLIENT_VERSION);
-            int ret = ReadAtCursor(pcursor, ssKey, ssValue);
+            int ret = batch.ReadAtCursor(pcursor, ssKey, ssValue);
             if (ret == DB_NOTFOUND)
                 break;
             else if (ret != 0)
@@ -664,14 +664,14 @@ DBErrors CWalletDB::FindWalletTx(std::vector<uint256>& vTxHash, std::vector<CWal
 
     try {
         int nMinVersion = 0;
-        if (Read((std::string)"minversion", nMinVersion))
+        if (batch.Read((std::string)"minversion", nMinVersion))
         {
             if (nMinVersion > CLIENT_VERSION)
                 return DB_TOO_NEW;
         }
 
         // Get cursor
-        Dbc* pcursor = GetCursor();
+        Dbc* pcursor = batch.GetCursor();
         if (!pcursor)
         {
             LogPrintf("Error getting wallet database cursor\n");
@@ -683,7 +683,7 @@ DBErrors CWalletDB::FindWalletTx(std::vector<uint256>& vTxHash, std::vector<CWal
             // Read next record
             CDataStream ssKey(SER_DISK, CLIENT_VERSION);
             CDataStream ssValue(SER_DISK, CLIENT_VERSION);
-            int ret = ReadAtCursor(pcursor, ssKey, ssValue);
+            int ret = batch.ReadAtCursor(pcursor, ssKey, ssValue);
             if (ret == DB_NOTFOUND)
                 break;
             else if (ret != 0)
@@ -797,9 +797,9 @@ void MaybeCompactWalletDB()
 
     if (nLastFlushed != CWalletDB::GetUpdateCounter() && GetTime() - nLastWalletUpdate >= 2)
     {
-        const std::string& strFile = pwalletMain->strWalletFile;
-        if (CDB::PeriodicFlush(strFile))
+        if (CDB::PeriodicFlush(pwalletMain->GetDBHandle())) {
             nLastFlushed = CWalletDB::GetUpdateCounter();
+        }
     }
     fOneThread = false;
 }
@@ -855,20 +855,20 @@ bool CWalletDB::VerifyDatabaseFile(const std::string& walletFile, const fs::path
 bool CWalletDB::WriteDestData(const std::string &address, const std::string &key, const std::string &value)
 {
     nWalletDBUpdateCounter++;
-    return Write(std::make_pair(std::string("destdata"), std::make_pair(address, key)), value);
+    return batch.Write(std::make_pair(std::string("destdata"), std::make_pair(address, key)), value);
 }
 
 bool CWalletDB::EraseDestData(const std::string &address, const std::string &key)
 {
     nWalletDBUpdateCounter++;
-    return Erase(std::make_pair(std::string("destdata"), std::make_pair(address, key)));
+    return batch.Erase(std::make_pair(std::string("destdata"), std::make_pair(address, key)));
 }
 
 
 bool CWalletDB::WriteHDChain(const CHDChain& chain)
 {
     nWalletDBUpdateCounter++;
-    return Write(std::string("hdchain"), chain);
+    return batch.Write(std::string("hdchain"), chain);
 }
 
 void CWalletDB::IncrementUpdateCounter()
@@ -880,3 +880,28 @@ unsigned int CWalletDB::GetUpdateCounter()
 {
     return nWalletDBUpdateCounter;
 }
+
+bool CWalletDB::TxnBegin()
+{
+    return batch.TxnBegin();
+}
+
+bool CWalletDB::TxnCommit()
+{
+    return batch.TxnCommit();
+}
+
+bool CWalletDB::TxnAbort()
+{
+    return batch.TxnAbort();
+}
+
+bool CWalletDB::ReadVersion(int& nVersion)
+{
+    return batch.ReadVersion(nVersion);
+}
+
+bool CWalletDB::WriteVersion(int nVersion)
+{
+    return batch.WriteVersion(nVersion);
+}
diff --git a/src/wallet/walletdb.h b/src/wallet/walletdb.h
index b94f341b2e..cd9fe279c5 100644
--- a/src/wallet/walletdb.h
+++ b/src/wallet/walletdb.h
@@ -17,6 +17,21 @@
 #include <utility>
 #include <vector>
 
+/**
+ * Overview of wallet database classes:
+ *
+ * - CDBEnv is an environment in which the database exists (has no analog in dbwrapper.h)
+ * - CWalletDBWrapper represents a wallet database (similar to CDBWrapper in dbwrapper.h)
+ * - CDB is a low-level database transaction (similar to CDBBatch in dbwrapper.h)
+ * - CWalletDB is a modifier object for the wallet, and encapsulates a database
+ *   transaction as well as methods to act on the database (no analog in
+ *   dbwrapper.h)
+ *
+ * The latter two are named confusingly, in contrast to what the names CDB
+ * and CWalletDB suggest they are transient transaction objects and don't
+ * represent the database itself.
+ */
+
 static const bool DEFAULT_FLUSHWALLET = true;
 
 class CAccount;
@@ -118,11 +133,16 @@ public:
     }
 };
 
-/** Access to the wallet database */
-class CWalletDB : public CDB
+/** Access to the wallet database.
+ * This should really be named CWalletDBBatch, as it represents a single transaction at the
+ * database. It will be committed when the object goes out of scope.
+ * Optionally (on by default) it will flush to disk as well.
+ */
+class CWalletDB
 {
 public:
-    CWalletDB(const std::string& strFilename, const char* pszMode = "r+", bool _fFlushOnClose = true) : CDB(strFilename, pszMode, _fFlushOnClose)
+    CWalletDB(CWalletDBWrapper& dbw, const char* pszMode = "r+", bool _fFlushOnClose = true) :
+        batch(dbw, pszMode, _fFlushOnClose)
     {
     }
 
@@ -194,7 +214,20 @@ public:
 
     static void IncrementUpdateCounter();
     static unsigned int GetUpdateCounter();
+
+    //! Begin a new transaction
+    bool TxnBegin();
+    //! Commit current transaction
+    bool TxnCommit();
+    //! Abort current transaction
+    bool TxnAbort();
+    //! Read wallet version
+    bool ReadVersion(int& nVersion);
+    //! Write wallet version
+    bool WriteVersion(int nVersion);
 private:
+    CDB batch;
+
     CWalletDB(const CWalletDB&);
     void operator=(const CWalletDB&);
 };