db: improve backups.

lib/db/lowlevelup.js

@@ -408,17 +408,20 @@ LowlevelUp.prototype.checkVersion = function checkVersion(key, version, callback
 
 LowlevelUp.prototype.clone = function clone(path, callback) {
   var self = this;
-  var options = { keys: true, values: true };
+  var iter = { keys: true, values: true };
+  var options = utils.merge({}, this.options);
+  var hwm = 256 << 20;
+  var total = 0;
   var tmp, batch;
 
   assert(!this.loading);
   assert(!this.closing);
   assert(this.loaded);
 
-  this.options.createIfMissing = true;
+  options.createIfMissing = true;
-  this.options.errorIfExists = true;
+  options.errorIfExists = true;
 
-  tmp = new LowlevelUp(path, this.options);
+  tmp = new LowlevelUp(path, options);
 
   function done(err) {
     tmp.close(function(e) {
@@ -434,10 +437,13 @@ LowlevelUp.prototype.clone = function clone(path, callback) {
 
     batch = tmp.batch();
 
-    self.each(options, function(key, value, next, i) {
+    self.each(iter, function(key, value, next) {
       batch.put(key, value);
 
-      if (i % 1000 === 0) {
+      total += value.length;
+
+      if (total >= hwm) {
+        total = 0;
         batch.write(function(err) {
           if (err)
             return next(err);

lib/http/rpc.js

@@ -2581,7 +2581,11 @@ RPC.prototype.backupwallet = function backupwallet(args, callback) {
 
   dest = toString(args[0]);
 
-  this.walletdb.db.backup(dest, callback);
+  this.walletdb.backup(dest, function(err) {
+    if (err)
+      return callback(err);
+    callback(null, null);
+  });
 };
 
 RPC.prototype.dumpprivkey = function dumpprivkey(args, callback) {

lib/wallet/walletdb.js

@@ -278,6 +278,16 @@ WalletDB.prototype._close = function close(callback) {
   });
 };
 
+/**
+ * Backup the wallet db.
+ * @param {String} path
+ * @param {Function} callback
+ */
+
+WalletDB.prototype.backup = function backup(path, callback) {
+  this.db.backup(path, callback);
+};
+
 /**
  * Get current wallet wid depth.
  * @private