wallet: Introduce database handle wrapper

Abstract database handle from explicit strFilename into
CWalletDBWrapper.

Also move CWallet::Backup to db.cpp - as it deals with representation
details this is a database specific operation.

8 files changed, 169 insertions, 96 deletions

diff --git a/src/wallet/db.cpp b/src/wallet/db.cpp
index f47fc92b57..cdf785a957 100644
--- a/src/wallet/db.cpp
+++ b/src/wallet/db.cpp
@@ -359,13 +359,12 @@ 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())
-        return;
+    const std::string& strFilename = dbw.strFile;
 
     bool fCreate = strchr(pszMode, 'c') != NULL;
     unsigned int nFlags = DB_THREAD;
@@ -472,8 +471,12 @@ 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.env) {
+        return true;
+    }
+    const std::string& strFile = dbw.strFile;
     while (true) {
         {
             LOCK(bitdb.cs_db);
@@ -487,7 +490,7 @@ bool CDB::Rewrite(const std::string& strFile, const char* pszSkip)
                 LogPrintf("CDB::Rewrite: Rewriting %s...\n", strFile);
                 std::string strFileRes = strFile + ".rewrite";
                 { // surround usage of db with extra {}
-                    CDB db(strFile.c_str(), "r");
+                    CDB db(dbw, "r");
                     Db* pdbCopy = new Db(bitdb.dbenv, 0);
 
                     int ret = pdbCopy->open(NULL,               // Txn pointer
@@ -596,9 +599,10 @@ void CDBEnv::Flush(bool fShutdown)
     }
 }
 
-bool CDB::PeriodicFlush(std::string strFile)
+bool CDB::PeriodicFlush(CWalletDBWrapper& dbw)
 {
     bool ret = false;
+    const std::string& strFile = dbw.strFile;
     TRY_LOCK(bitdb.cs_db,lockDb);
     if (lockDb)
     {
@@ -633,3 +637,45 @@ 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 (!env) {
+        return false;
+    }
+    while (true)
+    {
+        {
+            LOCK(bitdb.cs_db);
+            if (!bitdb.mapFileUseCount.count(strFile) || bitdb.mapFileUseCount[strFile] == 0)
+            {
+                // Flush log data to the dat file
+                bitdb.CloseDb(strFile);
+                bitdb.CheckpointLSN(strFile);
+                bitdb.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;
+}
diff --git a/src/wallet/db.h b/src/wallet/db.h
index 9f912f9a1a..f6d0d54114 100644
--- a/src/wallet/db.h
+++ b/src/wallet/db.h
@@ -86,6 +86,36 @@ 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:
+    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; }
+
+private:
+    /** BerkeleyDB specific */
+    CDBEnv *env;
+    std::string strFile;
+};
+
 
 /** RAII class that provides access to a Berkeley database */
 class CDB
@@ -97,7 +127,7 @@ protected:
     bool fReadOnly;
     bool fFlushOnClose;
 
-    explicit CDB(const std::string& strFilename, const char* pszMode = "r+", bool fFlushOnCloseIn=true);
+    explicit CDB(CWalletDBWrapper& dbw, const char* pszMode = "r+", bool fFlushOnCloseIn=true);
     ~CDB() { Close(); }
 
 public:
@@ -107,7 +137,7 @@ public:
 
     /* 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 */
@@ -310,7 +340,7 @@ 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 665d856df5..7408806b7d 100644
--- a/src/wallet/rpcwallet.cpp
+++ b/src/wallet/rpcwallet.cpp
@@ -2076,7 +2076,7 @@ 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 b5e26e26d3..5b03b00179 100644
--- a/src/wallet/wallet.cpp
+++ b/src/wallet/wallet.cpp
@@ -161,7 +161,7 @@ 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");
 }
 
@@ -183,7 +183,7 @@ bool CWallet::AddKeyPubKey(const CKey& secret, const CPubKey &pubkey)
     if (!fFileBacked)
         return true;
     if (!IsCrypted()) {
-        return CWalletDB(strWalletFile).WriteKey(pubkey,
+        return CWalletDB(*dbw).WriteKey(pubkey,
                                                  secret.GetPrivKey(),
                                                  mapKeyMetadata[pubkey.GetID()]);
     }
@@ -204,7 +204,7 @@ 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()]);
     }
@@ -242,7 +242,7 @@ bool CWallet::AddCScript(const CScript& 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)
@@ -270,7 +270,7 @@ bool CWallet::AddWatchOnly(const CScript& dest)
     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)
@@ -287,7 +287,7 @@ bool CWallet::RemoveWatchOnly(const CScript &dest)
     if (!HaveWatchOnly())
         NotifyWatchonlyChanged(false);
     if (fFileBacked)
-        if (!CWalletDB(strWalletFile).EraseWatchOnly(dest))
+        if (!CWalletDB(*dbw).EraseWatchOnly(dest))
             return false;
 
     return true;
@@ -353,7 +353,7 @@ 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;
@@ -366,7 +366,7 @@ bool CWallet::ChangeWalletPassphrase(const SecureString& strOldWalletPassphrase,
 
 void CWallet::SetBestChain(const CBlockLocator& loc)
 {
-    CWalletDB walletdb(strWalletFile);
+    CWalletDB walletdb(*dbw);
     walletdb.WriteBestBlock(loc);
 }
 
@@ -387,7 +387,7 @@ bool CWallet::SetMinVersion(enum WalletFeature nVersion, CWalletDB* pwalletdbIn,
 
     if (fFileBacked)
     {
-        CWalletDB* pwalletdb = pwalletdbIn ? pwalletdbIn : new CWalletDB(strWalletFile);
+        CWalletDB* pwalletdb = pwalletdbIn ? pwalletdbIn : new CWalletDB(*dbw);
         if (nWalletVersion > 40000)
             pwalletdb->WriteMinVersion(nWalletVersion);
         if (!pwalletdbIn)
@@ -597,7 +597,7 @@ bool CWallet::EncryptWallet(const SecureString& strWalletPassphrase)
         if (fFileBacked)
         {
             assert(!pwalletdbEncryption);
-            pwalletdbEncryption = new CWalletDB(strWalletFile);
+            pwalletdbEncryption = new CWalletDB(*dbw);
             if (!pwalletdbEncryption->TxnBegin()) {
                 delete pwalletdbEncryption;
                 pwalletdbEncryption = NULL;
@@ -651,7 +651,7 @@ 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);
@@ -662,7 +662,7 @@ 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
@@ -743,14 +743,14 @@ 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;
 
@@ -784,7 +784,7 @@ 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);
@@ -845,7 +845,7 @@ 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)) {
@@ -862,7 +862,7 @@ 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();
 
@@ -1006,7 +1006,7 @@ 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;
@@ -1078,7 +1078,7 @@ 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;
@@ -1361,7 +1361,7 @@ 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;
@@ -2758,13 +2758,13 @@ 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);
 }
@@ -2819,10 +2819,10 @@ 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();
@@ -2847,13 +2847,13 @@ DBErrors CWallet::ZapSelectTx(std::vector<uint256>& vHashIn, std::vector<uint256
         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.
@@ -2876,10 +2876,10 @@ 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();
@@ -2911,9 +2911,9 @@ bool CWallet::SetAddressBook(const CTxDestination& address, const std::string& s
                              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)
@@ -2927,7 +2927,7 @@ bool CWallet::DelAddressBook(const CTxDestination& 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);
@@ -2937,15 +2937,15 @@ bool CWallet::DelAddressBook(const CTxDestination& address)
 
     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))
+        if (!CWalletDB(*dbw).WriteDefaultKey(vchPubKey))
             return false;
     }
     vchDefaultKey = vchPubKey;
@@ -2960,7 +2960,7 @@ bool CWallet::NewKeyPool()
 {
     {
         LOCK(cs_wallet);
-        CWalletDB walletdb(strWalletFile);
+        CWalletDB walletdb(*dbw);
         BOOST_FOREACH(int64_t nIndex, setKeyPool)
             walletdb.ErasePool(nIndex);
         setKeyPool.clear();
@@ -2981,7 +2981,7 @@ 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;
@@ -3024,7 +3024,7 @@ 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;
@@ -3055,7 +3055,7 @@ 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)
@@ -3083,7 +3083,7 @@ void CWallet::KeepKey(int64_t nIndex)
     // Remove from key pool
     if (fFileBacked)
     {
-        CWalletDB walletdb(strWalletFile);
+        CWalletDB walletdb(*dbw);
         walletdb.ErasePool(nIndex);
     }
     LogPrintf("keypool keep %d\n", nIndex);
@@ -3127,7 +3127,7 @@ int64_t CWallet::GetOldestKeyPoolTime()
         return GetTime();
 
     CKeyPool keypool;
-    CWalletDB walletdb(strWalletFile);
+    CWalletDB walletdb(*dbw);
 
     if (IsHDEnabled() && CanSupportFeature(FEATURE_HD_SPLIT))
     {
@@ -3295,7 +3295,7 @@ 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);
 }
 
@@ -3375,7 +3375,7 @@ 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)
@@ -3599,7 +3599,7 @@ bool CWallet::AddDestData(const CTxDestination &dest, const std::string &key, co
     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)
@@ -3608,7 +3608,7 @@ bool CWallet::EraseDestData(const CTxDestination &dest, const std::string &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)
@@ -3678,7 +3678,8 @@ 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));
@@ -3693,7 +3694,8 @@ 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)
     {
@@ -3784,7 +3786,7 @@ 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);
@@ -3817,7 +3819,7 @@ 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)
             {
@@ -3979,36 +3981,7 @@ 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 06e7e14990..318aa2bf97 100644
--- a/src/wallet/wallet.h
+++ b/src/wallet/wallet.h
@@ -715,17 +715,35 @@ 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)
      */
     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)
     {
@@ -752,7 +770,7 @@ public:
         SetNull();
     }
 
-    CWallet(const std::string& strWalletFileIn) : strWalletFile(strWalletFileIn)
+    CWallet(std::unique_ptr<CWalletDBWrapper> dbw_in) : dbw(std::move(dbw_in))
     {
         SetNull();
         fFileBacked = true;
diff --git a/src/wallet/walletdb.cpp b/src/wallet/walletdb.cpp
index ceff2d36e3..6921c9900b 100644
--- a/src/wallet/walletdb.cpp
+++ b/src/wallet/walletdb.cpp
@@ -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;
 }
@@ -880,3 +880,4 @@ unsigned int CWalletDB::GetUpdateCounter()
 {
     return nWalletDBUpdateCounter;
 }
+
diff --git a/src/wallet/walletdb.h b/src/wallet/walletdb.h
index b94f341b2e..c0135a6292 100644
--- a/src/wallet/walletdb.h
+++ b/src/wallet/walletdb.h
@@ -118,11 +118,15 @@ public:
     }
 };
 
-/** Access to the wallet database */
+/** 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 CDB
 {
 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) : CDB(dbw, pszMode, _fFlushOnClose)
     {
     }