diff --git a/tests/client_tests/integration/test_transactions.py b/tests/client_tests/integration/test_transactions.py
index 572a2f000..93f49a0d7 100644
--- a/tests/client_tests/integration/test_transactions.py
+++ b/tests/client_tests/integration/test_transactions.py
@@ -10,10 +10,10 @@ class BasicTransactionTests(IntegrationTestCase):
 
     async def test_sending_and_receiving(self):
         account1, account2 = self.account, self.wallet.generate_account(self.ledger)
-        await self.ledger.update_account(account2)
+        await self.ledger.subscribe_account(account2)
 
-        self.assertEqual(await self.get_balance(account1), 0)
-        self.assertEqual(await self.get_balance(account2), 0)
+        await self.assertBalance(account1, '0.0')
+        await self.assertBalance(account2, '0.0')
 
         sendtxids = []
         for i in range(5):
@@ -26,8 +26,8 @@ class BasicTransactionTests(IntegrationTestCase):
             self.on_transaction_id(txid) for txid in sendtxids
         ])
 
-        self.assertEqual(round(await self.get_balance(account1)/COIN, 1), 5.5)
-        self.assertEqual(round(await self.get_balance(account2)/COIN, 1), 0)
+        await self.assertBalance(account1, '5.5')
+        await self.assertBalance(account2, '0.0')
 
         address2 = await account2.receiving.get_or_create_usable_address()
         hash2 = self.ledger.address_to_hash160(address2)
@@ -41,8 +41,8 @@ class BasicTransactionTests(IntegrationTestCase):
         await self.blockchain.generate(1)
         await self.ledger.wait(tx)  # confirmed
 
-        self.assertEqual(round(await self.get_balance(account1)/COIN, 1), 3.5)
-        self.assertEqual(round(await self.get_balance(account2)/COIN, 1), 2.0)
+        await self.assertBalance(account1, '3.499802')
+        await self.assertBalance(account2, '2.0')
 
         utxos = await self.account.get_utxos()
         tx = await self.ledger.transaction_class.create(
diff --git a/tests/client_tests/unit/test_account.py b/tests/client_tests/unit/test_account.py
index 8c50cea1c..b6a6d6895 100644
--- a/tests/client_tests/unit/test_account.py
+++ b/tests/client_tests/unit/test_account.py
@@ -44,7 +44,8 @@ class TestHierarchicalDeterministicAccount(AsyncioTestCase):
         self.assertEqual(len(addresses), 26)
 
     async def test_generate_keys_over_batch_threshold_saves_it_properly(self):
-        await self.account.receiving.generate_keys(0, 200)
+        async with self.account.receiving.address_generator_lock:
+            await self.account.receiving._generate_keys(0, 200)
         records = await self.account.receiving.get_address_records()
         self.assertEqual(201, len(records))
 
@@ -53,9 +54,10 @@ class TestHierarchicalDeterministicAccount(AsyncioTestCase):
 
         self.assertIsInstance(account.receiving, HierarchicalDeterministic)
 
-        await account.receiving.generate_keys(4, 7)
-        await account.receiving.generate_keys(0, 3)
-        await account.receiving.generate_keys(8, 11)
+        async with account.receiving.address_generator_lock:
+            await account.receiving._generate_keys(4, 7)
+            await account.receiving._generate_keys(0, 3)
+            await account.receiving._generate_keys(8, 11)
         records = await account.receiving.get_address_records()
         self.assertEqual(
             [r['position'] for r in records],
diff --git a/tests/client_tests/unit/test_database.py b/tests/client_tests/unit/test_database.py
index dcd241539..374280d52 100644
--- a/tests/client_tests/unit/test_database.py
+++ b/tests/client_tests/unit/test_database.py
@@ -128,7 +128,8 @@ class TestQueries(AsyncioTestCase):
         tx = ledger_class.transaction_class(height=height, is_verified=True) \
             .add_inputs([self.txi(self.txo(1, NULL_HASH))]) \
             .add_outputs([self.txo(1, to_hash)])
-        await self.ledger.db.save_transaction_io('insert', tx, to_address, to_hash, '')
+        await self.ledger.db.insert_transaction(tx)
+        await self.ledger.db.save_transaction_io(tx, to_address, to_hash, '')
         return tx
 
     async def create_tx_from_txo(self, txo, to_account, height):
@@ -139,8 +140,9 @@ class TestQueries(AsyncioTestCase):
         tx = ledger_class.transaction_class(height=height, is_verified=True) \
             .add_inputs([self.txi(txo)]) \
             .add_outputs([self.txo(1, to_hash)])
-        await self.ledger.db.save_transaction_io('insert', tx, from_address, from_hash, '')
-        await self.ledger.db.save_transaction_io('', tx, to_address, to_hash, '')
+        await self.ledger.db.insert_transaction(tx)
+        await self.ledger.db.save_transaction_io(tx, from_address, from_hash, '')
+        await self.ledger.db.save_transaction_io(tx, to_address, to_hash, '')
         return tx
 
     async def create_tx_to_nowhere(self, txo, height):
@@ -150,7 +152,8 @@ class TestQueries(AsyncioTestCase):
         tx = ledger_class.transaction_class(height=height, is_verified=True) \
             .add_inputs([self.txi(txo)]) \
             .add_outputs([self.txo(1, to_hash)])
-        await self.ledger.db.save_transaction_io('insert', tx, from_address, from_hash, '')
+        await self.ledger.db.insert_transaction(tx)
+        await self.ledger.db.save_transaction_io(tx, from_address, from_hash, '')
         return tx
 
     def txo(self, amount, address):
diff --git a/tests/client_tests/unit/test_ledger.py b/tests/client_tests/unit/test_ledger.py
index caa5b990c..0e077b441 100644
--- a/tests/client_tests/unit/test_ledger.py
+++ b/tests/client_tests/unit/test_ledger.py
@@ -16,6 +16,7 @@ class MockNetwork:
         self.address = None
         self.get_history_called = []
         self.get_transaction_called = []
+        self.is_connected = False
 
     async def get_history(self, address):
         self.get_history_called.append(address)
@@ -85,16 +86,21 @@ class TestSynchronization(LedgerTestCase):
             'abcd02': hexlify(get_transaction(get_output(2)).raw),
             'abcd03': hexlify(get_transaction(get_output(3)).raw),
         })
-        await self.ledger.update_history(address)
+        await self.ledger.update_history(address, '')
         self.assertEqual(self.ledger.network.get_history_called, [address])
         self.assertEqual(self.ledger.network.get_transaction_called, ['abcd01', 'abcd02', 'abcd03'])
 
         address_details = await self.ledger.db.get_address(address=address)
-        self.assertEqual(address_details['history'], 'abcd01:0:abcd02:1:abcd03:2:')
+        self.assertEqual(
+            address_details['history'],
+            '252bda9b22cc902ca2aa2de3548ee8baf06b8501ff7bfb3b0b7d980dbd1bf792:0:'
+            'ab9c0654dd484ac20437030f2034e25dcb29fc507e84b91138f80adc3af738f9:1:'
+            'a2ae3d1db3c727e7d696122cab39ee20a7f81856dab7019056dd539f38c548a0:2:'
+        )
 
         self.ledger.network.get_history_called = []
         self.ledger.network.get_transaction_called = []
-        await self.ledger.update_history(address)
+        await self.ledger.update_history(address, '')
         self.assertEqual(self.ledger.network.get_history_called, [address])
         self.assertEqual(self.ledger.network.get_transaction_called, [])
 
@@ -102,11 +108,17 @@ class TestSynchronization(LedgerTestCase):
         self.ledger.network.transaction['abcd04'] = hexlify(get_transaction(get_output(4)).raw)
         self.ledger.network.get_history_called = []
         self.ledger.network.get_transaction_called = []
-        await self.ledger.update_history(address)
+        await self.ledger.update_history(address, '')
         self.assertEqual(self.ledger.network.get_history_called, [address])
         self.assertEqual(self.ledger.network.get_transaction_called, ['abcd04'])
         address_details = await self.ledger.db.get_address(address=address)
-        self.assertEqual(address_details['history'], 'abcd01:0:abcd02:1:abcd03:2:abcd04:3:')
+        self.assertEqual(
+            address_details['history'],
+            '252bda9b22cc902ca2aa2de3548ee8baf06b8501ff7bfb3b0b7d980dbd1bf792:0:'
+            'ab9c0654dd484ac20437030f2034e25dcb29fc507e84b91138f80adc3af738f9:1:'
+            'a2ae3d1db3c727e7d696122cab39ee20a7f81856dab7019056dd539f38c548a0:2:'
+            '047cf1d53ef68f0fd586d46f90c09ff8e57a4180f67e7f4b8dd0135c3741e828:3:'
+        )
 
 
 class MocHeaderNetwork:
diff --git a/tests/client_tests/unit/test_transaction.py b/tests/client_tests/unit/test_transaction.py
index 8532f95fc..800c05322 100644
--- a/tests/client_tests/unit/test_transaction.py
+++ b/tests/client_tests/unit/test_transaction.py
@@ -261,14 +261,14 @@ class TransactionIOBalancing(AsyncioTestCase):
             .add_inputs([self.txi(self.txo(sum(amounts)+0.1))]) \
             .add_outputs(utxos)
 
-        save_tx = 'insert'
+        await self.ledger.db.insert_transaction(self.funding_tx)
+
         for utxo in utxos:
             await self.ledger.db.save_transaction_io(
-                save_tx, self.funding_tx,
+                self.funding_tx,
                 self.ledger.hash160_to_address(utxo.script.values['pubkey_hash']),
                 utxo.script.values['pubkey_hash'], ''
             )
-            save_tx = 'update'
 
         return utxos
 
diff --git a/tests/client_tests/unit/test_utils.py b/tests/client_tests/unit/test_utils.py
index 8bc368302..3d9e19d0a 100644
--- a/tests/client_tests/unit/test_utils.py
+++ b/tests/client_tests/unit/test_utils.py
@@ -1,6 +1,41 @@
 import unittest
 
 from torba.client.util import ArithUint256
+from torba.client.util import coins_to_satoshis as c2s, satoshis_to_coins as s2c
+
+
+class TestCoinValueParsing(unittest.TestCase):
+
+    def test_good_output(self):
+        self.assertEqual(s2c(1), "0.00000001")
+        self.assertEqual(s2c(10**7), "0.1")
+        self.assertEqual(s2c(2*10**8), "2.0")
+        self.assertEqual(s2c(2*10**17), "2000000000.0")
+
+    def test_good_input(self):
+        self.assertEqual(c2s("0.00000001"), 1)
+        self.assertEqual(c2s("0.1"), 10**7)
+        self.assertEqual(c2s("1.0"), 10**8)
+        self.assertEqual(c2s("2.00000000"), 2*10**8)
+        self.assertEqual(c2s("2000000000.0"), 2*10**17)
+
+    def test_bad_input(self):
+        with self.assertRaises(ValueError):
+            c2s("1")
+        with self.assertRaises(ValueError):
+            c2s("-1.0")
+        with self.assertRaises(ValueError):
+            c2s("10000000000.0")
+        with self.assertRaises(ValueError):
+            c2s("1.000000000")
+        with self.assertRaises(ValueError):
+            c2s("-0")
+        with self.assertRaises(ValueError):
+            c2s("1")
+        with self.assertRaises(ValueError):
+            c2s(".1")
+        with self.assertRaises(ValueError):
+            c2s("1e-7")
 
 
 class TestArithUint256(unittest.TestCase):
diff --git a/torba/client/baseaccount.py b/torba/client/baseaccount.py
index 9e9cf8d05..ad173f197 100644
--- a/torba/client/baseaccount.py
+++ b/torba/client/baseaccount.py
@@ -1,6 +1,7 @@
+import asyncio
 import random
 import typing
-from typing import Dict, Tuple, Type, Optional, Any
+from typing import Dict, Tuple, Type, Optional, Any, List
 
 from torba.client.mnemonic import Mnemonic
 from torba.client.bip32 import PrivateKey, PubKey, from_extended_key_string
@@ -15,12 +16,13 @@ class AddressManager:
 
     name: str
 
-    __slots__ = 'account', 'public_key', 'chain_number'
+    __slots__ = 'account', 'public_key', 'chain_number', 'address_generator_lock'
 
     def __init__(self, account, public_key, chain_number):
         self.account = account
         self.public_key = public_key
         self.chain_number = chain_number
+        self.address_generator_lock = asyncio.Lock()
 
     @classmethod
     def from_dict(cls, account: 'BaseAccount', d: dict) \
@@ -60,11 +62,11 @@ class AddressManager:
     def get_address_records(self, only_usable: bool = False, **constraints):
         raise NotImplementedError
 
-    async def get_addresses(self, only_usable: bool = False, **constraints):
+    async def get_addresses(self, only_usable: bool = False, **constraints) -> List[str]:
         records = await self.get_address_records(only_usable=only_usable, **constraints)
         return [r['address'] for r in records]
 
-    async def get_or_create_usable_address(self):
+    async def get_or_create_usable_address(self) -> str:
         addresses = await self.get_addresses(only_usable=True, limit=10)
         if addresses:
             return random.choice(addresses)
@@ -87,8 +89,8 @@ class HierarchicalDeterministic(AddressManager):
     @classmethod
     def from_dict(cls, account: 'BaseAccount', d: dict) -> Tuple[AddressManager, AddressManager]:
         return (
-            cls(account, 0, **d.get('receiving', {'gap': 20, 'maximum_uses_per_address': 2})),
-            cls(account, 1, **d.get('change', {'gap': 6, 'maximum_uses_per_address': 2}))
+            cls(account, 0, **d.get('receiving', {'gap': 20, 'maximum_uses_per_address': 1})),
+            cls(account, 1, **d.get('change', {'gap': 6, 'maximum_uses_per_address': 1}))
         )
 
     def to_dict_instance(self):
@@ -97,19 +99,7 @@ class HierarchicalDeterministic(AddressManager):
     def get_private_key(self, index: int) -> PrivateKey:
         return self.account.private_key.child(self.chain_number).child(index)
 
-    async def generate_keys(self, start: int, end: int):
-        keys_batch, final_keys = [], []
-        for index in range(start, end+1):
-            keys_batch.append((index, self.public_key.child(index)))
-            if index % 180 == 0 or index == end:
-                await self.account.ledger.db.add_keys(
-                    self.account, self.chain_number, keys_batch
-                )
-                final_keys.extend(keys_batch)
-                keys_batch.clear()
-        return [key[1].address for key in final_keys]
-
-    async def get_max_gap(self):
+    async def get_max_gap(self) -> int:
         addresses = await self._query_addresses(order_by="position ASC")
         max_gap = 0
         current_gap = 0
@@ -121,27 +111,43 @@ class HierarchicalDeterministic(AddressManager):
                 current_gap = 0
         return max_gap
 
-    async def ensure_address_gap(self):
-        addresses = await self._query_addresses(limit=self.gap, order_by="position DESC")
+    async def ensure_address_gap(self) -> List[str]:
+        async with self.address_generator_lock:
+            addresses = await self._query_addresses(limit=self.gap, order_by="position DESC")
 
-        existing_gap = 0
-        for address in addresses:
-            if address['used_times'] == 0:
-                existing_gap += 1
-            else:
-                break
+            existing_gap = 0
+            for address in addresses:
+                if address['used_times'] == 0:
+                    existing_gap += 1
+                else:
+                    break
 
-        if existing_gap == self.gap:
-            return []
+            if existing_gap == self.gap:
+                return []
 
-        start = addresses[0]['position']+1 if addresses else 0
-        end = start + (self.gap - existing_gap)
-        new_keys = await self.generate_keys(start, end-1)
-        return new_keys
+            start = addresses[0]['position']+1 if addresses else 0
+            end = start + (self.gap - existing_gap)
+            new_keys = await self._generate_keys(start, end-1)
+            await self.account.ledger.subscribe_addresses(self, new_keys)
+            return new_keys
+
+    async def _generate_keys(self, start: int, end: int) -> List[str]:
+        if not self.address_generator_lock.locked():
+            raise RuntimeError('Should not be called outside of address_generator_lock.')
+        keys_batch, final_keys = [], []
+        for index in range(start, end+1):
+            keys_batch.append((index, self.public_key.child(index)))
+            if index % 180 == 0 or index == end:
+                await self.account.ledger.db.add_keys(
+                    self.account, self.chain_number, keys_batch
+                )
+                final_keys.extend(keys_batch)
+                keys_batch.clear()
+        return [key[1].address for key in final_keys]
 
     def get_address_records(self, only_usable: bool = False, **constraints):
         if only_usable:
-            constraints['used_times__lte'] = self.maximum_uses_per_address
+            constraints['used_times__lt'] = self.maximum_uses_per_address
         return self._query_addresses(order_by="used_times ASC, position ASC", **constraints)
 
 
@@ -164,17 +170,20 @@ class SingleKey(AddressManager):
     def get_private_key(self, index: int) -> PrivateKey:
         return self.account.private_key
 
-    async def get_max_gap(self):
+    async def get_max_gap(self) -> int:
         return 0
 
-    async def ensure_address_gap(self):
-        exists = await self.get_address_records()
-        if not exists:
-            await self.account.ledger.db.add_keys(
-                self.account, self.chain_number, [(0, self.public_key)]
-            )
-            return [self.public_key.address]
-        return []
+    async def ensure_address_gap(self) -> List[str]:
+        async with self.address_generator_lock:
+            exists = await self.get_address_records()
+            if not exists:
+                await self.account.ledger.db.add_keys(
+                    self.account, self.chain_number, [(0, self.public_key)]
+                )
+                new_keys = [self.public_key.address]
+                await self.account.ledger.subscribe_addresses(self, new_keys)
+                return new_keys
+            return []
 
     def get_address_records(self, only_usable: bool = False, **constraints):
         return self._query_addresses(**constraints)
@@ -211,7 +220,7 @@ class BaseAccount:
         generator_name = address_generator.get('name', HierarchicalDeterministic.name)
         self.address_generator = self.address_generators[generator_name]
         self.receiving, self.change = self.address_generator.from_dict(self, address_generator)
-        self.address_managers = {self.receiving, self.change}
+        self.address_managers = {am.chain_number: am for am in {self.receiving, self.change}}
         ledger.add_account(self)
         wallet.add_account(self)
 
@@ -320,12 +329,12 @@ class BaseAccount:
 
     async def ensure_address_gap(self):
         addresses = []
-        for address_manager in self.address_managers:
+        for address_manager in self.address_managers.values():
             new_addresses = await address_manager.ensure_address_gap()
             addresses.extend(new_addresses)
         return addresses
 
-    async def get_addresses(self, **constraints):
+    async def get_addresses(self, **constraints) -> List[str]:
         rows = await self.ledger.db.select_addresses('address', account=self, **constraints)
         return [r[0] for r in rows]
 
@@ -337,8 +346,7 @@ class BaseAccount:
 
     def get_private_key(self, chain: int, index: int) -> PrivateKey:
         assert not self.encrypted, "Cannot get private key on encrypted wallet account."
-        address_manager = {0: self.receiving, 1: self.change}[chain]
-        return address_manager.get_private_key(index)
+        return self.address_managers[chain].get_private_key(index)
 
     def get_balance(self, confirmations: int = 0, **constraints):
         if confirmations > 0:
diff --git a/torba/client/basedatabase.py b/torba/client/basedatabase.py
index c64fedff6..dc5a1d93f 100644
--- a/torba/client/basedatabase.py
+++ b/torba/client/basedatabase.py
@@ -169,13 +169,16 @@ class SQLiteMixin:
         await self.db.close()
 
     @staticmethod
-    def _insert_sql(table: str, data: dict) -> Tuple[str, List]:
+    def _insert_sql(table: str, data: dict, ignore_duplicate: bool = False) -> Tuple[str, List]:
         columns, values = [], []
         for column, value in data.items():
             columns.append(column)
             values.append(value)
-        sql = "INSERT INTO {} ({}) VALUES ({})".format(
-            table, ', '.join(columns), ', '.join(['?'] * len(values))
+        or_ignore = ""
+        if ignore_duplicate:
+            or_ignore = " OR IGNORE"
+        sql = "INSERT{} INTO {} ({}) VALUES ({})".format(
+            or_ignore, table, ', '.join(columns), ', '.join(['?'] * len(values))
         )
         return sql, values
 
@@ -273,60 +276,49 @@ class BaseDatabase(SQLiteMixin):
             'script': sqlite3.Binary(txo.script.source)
         }
 
-    def save_transaction_io(self, save_tx, tx: BaseTransaction, address, txhash, history):
+    async def insert_transaction(self, tx):
+        await self.db.execute(*self._insert_sql('tx', {
+            'txid': tx.id,
+            'raw': sqlite3.Binary(tx.raw),
+            'height': tx.height,
+            'position': tx.position,
+            'is_verified': tx.is_verified
+        }))
 
-        def _transaction(conn: sqlite3.Connection, save_tx, tx: BaseTransaction, address, txhash, history):
-            if save_tx == 'insert':
-                conn.execute(*self._insert_sql('tx', {
-                    'txid': tx.id,
-                    'raw': sqlite3.Binary(tx.raw),
-                    'height': tx.height,
-                    'position': tx.position,
-                    'is_verified': tx.is_verified
-                }))
-            elif save_tx == 'update':
-                conn.execute(*self._update_sql("tx", {
-                    'height': tx.height, 'position': tx.position, 'is_verified': tx.is_verified
-                }, 'txid = ?', (tx.id,)))
+    async def update_transaction(self, tx):
+        await self.db.execute(*self._update_sql("tx", {
+            'height': tx.height, 'position': tx.position, 'is_verified': tx.is_verified
+        }, 'txid = ?', (tx.id,)))
 
-            existing_txos = set(map(itemgetter(0), conn.execute(*query(
-                "SELECT position FROM txo", txid=tx.id
-            ))))
+    def save_transaction_io(self, tx: BaseTransaction, address, txhash, history):
+
+        def _transaction(conn: sqlite3.Connection, tx: BaseTransaction, address, txhash, history):
 
             for txo in tx.outputs:
-                if txo.position in existing_txos:
-                    continue
                 if txo.script.is_pay_pubkey_hash and txo.script.values['pubkey_hash'] == txhash:
-                    conn.execute(*self._insert_sql("txo", self.txo_to_row(tx, address, txo)))
+                    conn.execute(*self._insert_sql(
+                        "txo", self.txo_to_row(tx, address, txo), ignore_duplicate=True
+                    ))
                 elif txo.script.is_pay_script_hash:
                     # TODO: implement script hash payments
                     log.warning('Database.save_transaction_io: pay script hash is not implemented!')
 
-            # lookup the address associated with each TXI (via its TXO)
-            txoid_to_address = {r[0]: r[1] for r in conn.execute(*query(
-                "SELECT txoid, address FROM txo", txoid__in=[txi.txo_ref.id for txi in tx.inputs]
-            ))}
-
-            # list of TXIs that have already been added
-            existing_txis = {r[0] for r in conn.execute(*query(
-                "SELECT txoid FROM txi", txid=tx.id
-            ))}
-
             for txi in tx.inputs:
-                txoid = txi.txo_ref.id
-                new_txi = txoid not in existing_txis
-                address_matches = txoid_to_address.get(txoid) == address
-                if new_txi and address_matches:
-                    conn.execute(*self._insert_sql("txi", {
-                        'txid': tx.id,
-                        'txoid': txoid,
-                        'address': address,
-                    }))
+                if txi.txo_ref.txo is not None:
+                    txo = txi.txo_ref.txo
+                    if txo.get_address(self.ledger) == address:
+                        conn.execute(*self._insert_sql("txi", {
+                            'txid': tx.id,
+                            'txoid': txo.id,
+                            'address': address,
+                        }, ignore_duplicate=True))
+
             conn.execute(
                 "UPDATE pubkey_address SET history = ?, used_times = ? WHERE address = ?",
                 (history, history.count(':')//2, address)
             )
-        return self.db.run(_transaction, save_tx, tx, address, txhash, history)
+
+        return self.db.run(_transaction, tx, address, txhash, history)
 
     async def reserve_outputs(self, txos, is_reserved=True):
         txoids = [txo.id for txo in txos]
diff --git a/torba/client/baseledger.py b/torba/client/baseledger.py
index 11a603802..6fd86b008 100644
--- a/torba/client/baseledger.py
+++ b/torba/client/baseledger.py
@@ -5,7 +5,7 @@ from functools import partial
 from binascii import hexlify, unhexlify
 from io import StringIO
 
-from typing import Dict, Type, Iterable
+from typing import Dict, Type, Iterable, List, Optional
 from operator import itemgetter
 from collections import namedtuple
 
@@ -48,6 +48,51 @@ class BlockHeightEvent(namedtuple('BlockHeightEvent', ('height', 'change'))):
     pass
 
 
+class TransactionCacheItem:
+    __slots__ = '_tx', 'lock', 'has_tx'
+
+    def __init__(self,
+            tx: Optional[basetransaction.BaseTransaction] = None,
+            lock: Optional[asyncio.Lock] = None):
+        self.has_tx = asyncio.Event()
+        self.lock = lock or asyncio.Lock()
+        self.tx = tx
+
+    @property
+    def tx(self):
+        return self._tx
+
+    @tx.setter
+    def tx(self, tx):
+        self._tx = tx
+        if tx is not None:
+            self.has_tx.set()
+
+
+class SynchronizationMonitor:
+
+    def __init__(self):
+        self.done = asyncio.Event()
+        self.tasks = []
+
+    def add(self, coro):
+        len(self.tasks) < 1 and self.done.clear()
+        asyncio.ensure_future(self._monitor(coro))
+
+    def cancel(self):
+        for task in self.tasks:
+            task.cancel()
+
+    async def _monitor(self, coro):
+        task = asyncio.ensure_future(coro)
+        self.tasks.append(task)
+        try:
+            await task
+        finally:
+            self.tasks.remove(task)
+            len(self.tasks) < 1 and self.done.set()
+
+
 class BaseLedger(metaclass=LedgerRegistry):
 
     name: str
@@ -79,7 +124,8 @@ class BaseLedger(metaclass=LedgerRegistry):
         )
         self.network = self.config.get('network') or self.network_class(self)
         self.network.on_header.listen(self.receive_header)
-        self.network.on_status.listen(self.receive_status)
+        self.network.on_status.listen(self.process_status_update)
+
         self.accounts = []
         self.fee_per_byte: int = self.config.get('fee_per_byte', self.default_fee_per_byte)
 
@@ -101,7 +147,8 @@ class BaseLedger(metaclass=LedgerRegistry):
             )
         )
 
-        self._transaction_processing_locks = {}
+        self._tx_cache = {}
+        self.sync = SynchronizationMonitor()
         self._utxo_reservation_lock = asyncio.Lock()
         self._header_processing_lock = asyncio.Lock()
 
@@ -166,16 +213,14 @@ class BaseLedger(metaclass=LedgerRegistry):
     def release_outputs(self, txos):
         return self.db.release_outputs(txos)
 
-    async def get_local_status(self, address):
-        address_details = await self.db.get_address(address=address)
-        history = address_details['history']
-        return hexlify(sha256(history.encode())).decode() if history else None
-
-    async def get_local_history(self, address):
+    async def get_local_status_and_history(self, address):
         address_details = await self.db.get_address(address=address)
         history = address_details['history'] or ''
         parts = history.split(':')[:-1]
-        return list(zip(parts[0::2], map(int, parts[1::2])))
+        return (
+            hexlify(sha256(history.encode())).decode() if history else None,
+            list(zip(parts[0::2], map(int, parts[1::2])))
+        )
 
     @staticmethod
     def get_root_of_merkle_tree(branches, branch_positions, working_branch):
@@ -189,21 +234,13 @@ class BaseLedger(metaclass=LedgerRegistry):
             working_branch = double_sha256(combined)
         return hexlify(working_branch[::-1])
 
-    async def validate_transaction_and_set_position(self, tx, height, merkle):
-        if not height <= len(self.headers):
-            return False
-        merkle_root = self.get_root_of_merkle_tree(merkle['merkle'], merkle['pos'], tx.hash)
-        header = self.headers[height]
-        tx.position = merkle['pos']
-        tx.is_verified = merkle_root == header['merkle_root']
-
     async def start(self):
         if not os.path.exists(self.path):
             os.mkdir(self.path)
-        await asyncio.gather(
+        await asyncio.wait([
             self.db.open(),
             self.headers.open()
-        )
+        ])
         first_connection = self.network.on_connected.first
         asyncio.ensure_future(self.network.start())
         await first_connection
@@ -214,9 +251,15 @@ class BaseLedger(metaclass=LedgerRegistry):
         log.info("Subscribing and updating accounts.")
         await self.update_headers()
         await self.network.subscribe_headers()
-        await self.update_accounts()
+        import time
+        start = time.time()
+        await self.subscribe_accounts()
+        await self.sync.done.wait()
+        log.info(f'elapsed: {time.time()-start}')
 
     async def stop(self):
+        self.sync.cancel()
+        await self.sync.done.wait()
         await self.network.stop()
         await self.db.close()
         await self.headers.close()
@@ -299,89 +342,144 @@ class BaseLedger(metaclass=LedgerRegistry):
                 height=header['height'], headers=header['hex'], subscription_update=True
             )
 
-    async def update_accounts(self):
-        return await asyncio.gather(*(
-            self.update_account(a) for a in self.accounts
-        ))
+    async def subscribe_accounts(self):
+        if self.network.is_connected and self.accounts:
+            await asyncio.wait([
+                self.subscribe_account(a) for a in self.accounts
+            ])
 
-    async def update_account(self, account: baseaccount.BaseAccount):
+    async def subscribe_account(self, account: baseaccount.BaseAccount):
+        for address_manager in account.address_managers.values():
+            await self.subscribe_addresses(address_manager, await address_manager.get_addresses())
         await account.ensure_address_gap()
-        addresses = await account.get_addresses()
-        while addresses:
-            await asyncio.gather(*(self.subscribe_history(a) for a in addresses))
-            addresses = await account.ensure_address_gap()
 
-    def _prefetch_history(self, remote_history, local_history):
-        proofs, network_txs = {}, {}
-        for i, (hex_id, remote_height) in enumerate(map(itemgetter('tx_hash', 'height'), remote_history)):
-            if i < len(local_history) and local_history[i] == (hex_id, remote_height):
-                continue
-            if remote_height > 0:
-                proofs[hex_id] = asyncio.ensure_future(self.network.get_merkle(hex_id, remote_height))
-            network_txs[hex_id] = asyncio.ensure_future(self.network.get_transaction(hex_id))
-        return proofs, network_txs
+    async def subscribe_addresses(self, address_manager: baseaccount.AddressManager, addresses: List[str]):
+        if self.network.is_connected and addresses:
+            await asyncio.wait([
+                self.subscribe_address(address_manager, address) for address in addresses
+            ])
 
-    async def update_history(self, address):
-        remote_history = await self.network.get_history(address)
-        local_history = await self.get_local_history(address)
-        proofs, network_txs = self._prefetch_history(remote_history, local_history)
-
-        synced_history = StringIO()
-        for i, (hex_id, remote_height) in enumerate(map(itemgetter('tx_hash', 'height'), remote_history)):
-
-            synced_history.write('{}:{}:'.format(hex_id, remote_height))
-
-            if i < len(local_history) and local_history[i] == (hex_id, remote_height):
-                continue
-
-            lock = self._transaction_processing_locks.setdefault(hex_id, asyncio.Lock())
-
-            await lock.acquire()
-
-            try:
-
-                # see if we have a local copy of transaction, otherwise fetch it from server
-                tx = await self.db.get_transaction(txid=hex_id)
-                save_tx = None
-                if tx is None:
-                    _raw = await network_txs[hex_id]
-                    tx = self.transaction_class(unhexlify(_raw))
-                    save_tx = 'insert'
-
-                tx.height = remote_height
-
-                if remote_height > 0 and (not tx.is_verified or tx.position == -1):
-                    await self.validate_transaction_and_set_position(tx, remote_height, await proofs[hex_id])
-                    if save_tx is None:
-                        save_tx = 'update'
-
-                await self.db.save_transaction_io(
-                    save_tx, tx, address, self.address_to_hash160(address), synced_history.getvalue()
-                )
-
-                log.debug(
-                    "%s: sync'ed tx %s for address: %s, height: %s, verified: %s",
-                    self.get_id(), hex_id, address, tx.height, tx.is_verified
-                )
-
-                self._on_transaction_controller.add(TransactionEvent(address, tx))
-
-            finally:
-                lock.release()
-                if not lock.locked() and hex_id in self._transaction_processing_locks:
-                    del self._transaction_processing_locks[hex_id]
-
-    async def subscribe_history(self, address):
+    async def subscribe_address(self, address_manager: baseaccount.AddressManager, address: str):
         remote_status = await self.network.subscribe_address(address)
-        local_status = await self.get_local_status(address)
-        if local_status != remote_status:
-            await self.update_history(address)
+        self.sync.add(self.update_history(address, remote_status, address_manager))
 
-    async def receive_status(self, response):
-        address, remote_status = response
-        local_status = await self.get_local_status(address)
-        if local_status != remote_status:
-            await self.update_history(address)
+    def process_status_update(self, update):
+        address, remote_status = update
+        self.sync.add(self.update_history(address, remote_status))
+
+    async def update_history(self, address, remote_status,
+                             address_manager: baseaccount.AddressManager = None):
+        local_status, local_history = await self.get_local_status_and_history(address)
+
+        if local_status == remote_status:
+            return
+
+        remote_history = await self.network.get_history(address)
+
+        cache_tasks = []
+        synced_history = StringIO()
+        for i, (txid, remote_height) in enumerate(map(itemgetter('tx_hash', 'height'), remote_history)):
+            if i < len(local_history) and local_history[i] == (txid, remote_height):
+                synced_history.write(f'{txid}:{remote_height}:')
+            else:
+                cache_tasks.append(asyncio.ensure_future(
+                    self.cache_transaction(txid, remote_height)
+                ))
+
+        for task in cache_tasks:
+            tx = await task
+
+            check_db_for_txos = []
+            for txi in tx.inputs:
+                if txi.txo_ref.txo is not None:
+                    continue
+                cache_item = self._tx_cache.get(txi.txo_ref.tx_ref.id)
+                if cache_item is not None:
+                    if cache_item.tx is None:
+                        await cache_item.has_tx.wait()
+                    txi.txo_ref = cache_item.tx.outputs[txi.txo_ref.position].ref
+                else:
+                    check_db_for_txos.append(txi.txo_ref.tx_ref.id)
+
+            referenced_txos = {
+                txo.id: txo for txo in await self.db.get_txos(txoid__in=check_db_for_txos)
+            }
+
+            for txi in tx.inputs:
+                if txi.txo_ref.txo is not None:
+                    continue
+                referenced_txo = referenced_txos.get(txi.txo_ref.tx_ref.id)
+                if referenced_txos:
+                    txi.txo_ref = referenced_txo.ref
+
+            synced_history.write(f'{tx.id}:{tx.height}:')
+
+            await self.db.save_transaction_io(
+                tx, address, self.address_to_hash160(address), synced_history.getvalue()
+            )
+
+            self._on_transaction_controller.add(TransactionEvent(address, tx))
+
+        if address_manager is None:
+            address_manager = await self.get_address_manager_for_address(address)
+
+        await address_manager.ensure_address_gap()
+
+    async def cache_transaction(self, txid, remote_height):
+        cache_item = self._tx_cache.get(txid)
+        if cache_item is None:
+            cache_item = self._tx_cache[txid] = TransactionCacheItem()
+        elif cache_item.tx is not None and \
+                cache_item.tx.height >= remote_height and \
+                (cache_item.tx.is_verified or remote_height < 1):
+            return cache_item.tx  # cached tx is already up-to-date
+
+        await cache_item.lock.acquire()
+
+        try:
+            tx = cache_item.tx
+
+            if tx is None:
+                # check local db
+                tx = cache_item.tx = await self.db.get_transaction(txid=txid)
+
+            if tx is None:
+                # fetch from network
+                _raw = await self.network.get_transaction(txid)
+                if _raw:
+                    tx = self.transaction_class(unhexlify(_raw))
+                    await self.maybe_verify_transaction(tx, remote_height)
+                    await self.db.insert_transaction(tx)
+                    cache_item.tx = tx  # make sure it's saved before caching it
+                    return tx
+
+            if tx is None:
+                raise ValueError(f'Transaction {txid} was not in database and not on network.')
+
+            if 0 < remote_height and not tx.is_verified:
+                # tx from cache / db is not up-to-date
+                await self.maybe_verify_transaction(tx, remote_height)
+                await self.db.update_transaction(tx)
+
+            return tx
+
+        finally:
+            cache_item.lock.release()
+
+    async def maybe_verify_transaction(self, tx, remote_height):
+        tx.height = remote_height
+        if 0 < remote_height <= len(self.headers):
+            merkle = await self.network.get_merkle(tx.id, remote_height)
+            merkle_root = self.get_root_of_merkle_tree(merkle['merkle'], merkle['pos'], tx.hash)
+            header = self.headers[remote_height]
+            tx.position = merkle['pos']
+            tx.is_verified = merkle_root == header['merkle_root']
+
+    async def get_address_manager_for_address(self, address) -> baseaccount.AddressManager:
+        details = await self.db.get_address(address=address)
+        for account in self.accounts:
+            if account.id == details['account']:
+                return account.address_managers[details['chain']]
 
     def broadcast(self, tx):
         return self.network.broadcast(hexlify(tx.raw).decode())
diff --git a/torba/client/util.py b/torba/client/util.py
index 8ae838027..f57963a89 100644
--- a/torba/client/util.py
+++ b/torba/client/util.py
@@ -1,5 +1,25 @@
+import re
 from binascii import unhexlify, hexlify
 from typing import TypeVar, Sequence, Optional
+from torba.client.constants import COIN
+
+
+def coins_to_satoshis(coins):
+    if not isinstance(coins, str):
+        raise ValueError("{coins} must be a string")
+    result = re.search(r'^(\d{1,10})\.(\d{1,8})$', coins)
+    if result is not None:
+        whole, fractional = result.groups()
+        return int(whole+fractional.ljust(8, "0"))
+    raise ValueError("'{lbc}' is not a valid coin decimal")
+
+
+def satoshis_to_coins(satoshis):
+    coins = '{:.8f}'.format(satoshis / COIN).rstrip('0')
+    if coins.endswith('.'):
+        return coins+'0'
+    else:
+        return coins
 
 
 T = TypeVar('T')
diff --git a/torba/orchstr8/node.py b/torba/orchstr8/node.py
index 7ebd2f879..46c9b9bb1 100644
--- a/torba/orchstr8/node.py
+++ b/torba/orchstr8/node.py
@@ -112,7 +112,7 @@ class Conductor:
 class WalletNode:
 
     def __init__(self, manager_class: Type[BaseWalletManager], ledger_class: Type[BaseLedger],
-                 verbose: bool = False) -> None:
+                 verbose: bool = False, api_port: int = 5279) -> None:
         self.manager_class = manager_class
         self.ledger_class = ledger_class
         self.verbose = verbose
@@ -121,8 +121,9 @@ class WalletNode:
         self.wallet: Optional[Wallet] = None
         self.account: Optional[BaseAccount] = None
         self.data_path: Optional[str] = None
+        self.api_port = api_port
 
-    async def start(self):
+    async def start(self, seed=None):
         self.data_path = tempfile.mkdtemp()
         wallet_file_name = os.path.join(self.data_path, 'my_wallet.json')
         with open(wallet_file_name, 'w') as wallet_file:
@@ -130,6 +131,7 @@ class WalletNode:
         self.manager = self.manager_class.from_config({
             'ledgers': {
                 self.ledger_class.get_id(): {
+                    'api_port': self.api_port,
                     'default_servers': [('localhost', 1984)],
                     'data_path': self.data_path
                 }
@@ -138,7 +140,12 @@ class WalletNode:
         })
         self.ledger = self.manager.ledgers[self.ledger_class]
         self.wallet = self.manager.default_wallet
-        self.wallet.generate_account(self.ledger)
+        if seed is None:
+            self.wallet.generate_account(self.ledger)
+        else:
+            self.ledger.account_class.from_dict(
+                self.ledger, self.wallet, {'seed': seed}
+            )
         self.account = self.wallet.default_account
         await self.manager.start()
 
diff --git a/torba/stream.py b/torba/stream.py
index 64c1f5e10..40589ade0 100644
--- a/torba/stream.py
+++ b/torba/stream.py
@@ -29,18 +29,18 @@ class BroadcastSubscription:
 
     def _add(self, data):
         if self.can_fire and self._on_data is not None:
-            maybe_coroutine = self._on_data(data)
-            if asyncio.iscoroutine(maybe_coroutine):
-                asyncio.ensure_future(maybe_coroutine)
+            return self._on_data(data)
 
     def _add_error(self, exception):
         if self.can_fire and self._on_error is not None:
-            self._on_error(exception)
+            return self._on_error(exception)
 
     def _close(self):
-        if self.can_fire and self._on_done is not None:
-            self._on_done()
-        self.is_closed = True
+        try:
+            if self.can_fire and self._on_done is not None:
+                return self._on_done()
+        finally:
+            self.is_closed = True
 
 
 class StreamController:
@@ -62,13 +62,28 @@ class StreamController:
             next_sub = next_sub._next
             yield subscription
 
-    def add(self, event):
+    def _notify_and_ensure_future(self, notify):
+        tasks = []
         for subscription in self._iterate_subscriptions:
-            subscription._add(event)
+            maybe_coroutine = notify(subscription)
+            if asyncio.iscoroutine(maybe_coroutine):
+                tasks.append(maybe_coroutine)
+        if tasks:
+            return asyncio.ensure_future(asyncio.wait(tasks))
+        else:
+            f = asyncio.get_event_loop().create_future()
+            f.set_result(None)
+            return f
+
+    def add(self, event):
+        return self._notify_and_ensure_future(
+            lambda subscription: subscription._add(event)
+        )
 
     def add_error(self, exception):
-        for subscription in self._iterate_subscriptions:
-            subscription._add_error(exception)
+        return self._notify_and_ensure_future(
+            lambda subscription: subscription._add_error(exception)
+        )
 
     def close(self):
         for subscription in self._iterate_subscriptions:
diff --git a/torba/testcase.py b/torba/testcase.py
index d8f1f9ef0..30c2f3526 100644
--- a/torba/testcase.py
+++ b/torba/testcase.py
@@ -9,6 +9,7 @@ from torba.client.baseledger import BaseLedger
 from torba.client.baseaccount import BaseAccount
 from torba.client.basemanager import BaseWalletManager
 from torba.client.wallet import Wallet
+from torba.client.util import satoshis_to_coins
 
 
 try:
@@ -159,15 +160,13 @@ class IntegrationTestCase(AsyncioTestCase):
     async def asyncTearDown(self):
         await self.conductor.stop()
 
+    async def assertBalance(self, account, expected_balance: str):
+        balance = await account.get_balance()
+        self.assertEqual(satoshis_to_coins(balance), expected_balance)
+
     def broadcast(self, tx):
         return self.ledger.broadcast(tx)
 
-    def get_balance(self, account=None, confirmations=0):
-        if account is None:
-            return self.manager.get_balance(confirmations=confirmations)
-        else:
-            return account.get_balance(confirmations=confirmations)
-
     async def on_header(self, height):
         if self.ledger.headers.height < height:
             await self.ledger.on_header.where(
@@ -175,8 +174,8 @@ class IntegrationTestCase(AsyncioTestCase):
             )
         return True
 
-    def on_transaction_id(self, txid):
-        return self.ledger.on_transaction.where(
+    def on_transaction_id(self, txid, ledger=None):
+        return (ledger or self.ledger).on_transaction.where(
             lambda e: e.tx.id == txid
         )