diff --git a/docs/source/conf.py b/docs/source/conf.py
index d4771f1..e61b737 100644
--- a/docs/source/conf.py
+++ b/docs/source/conf.py
@@ -9,7 +9,7 @@
 project = 'ptvp35'
 copyright = '2022, PARRRATE TNV'
 author = 'PARRRATE TNV'
-release = '1.0rc3'
+release = '1.0rc4'
 
 # -- General configuration ---------------------------------------------------
 # https://www.sphinx-doc.org/en/master/usage/configuration.html#general-configuration
diff --git a/docs/source/usage.rst b/docs/source/usage.rst
index 4aa87ae..8812bc3 100644
--- a/docs/source/usage.rst
+++ b/docs/source/usage.rst
@@ -8,7 +8,7 @@ Default installation option is to use pip+git
 
 .. code-block:: console
 
-    (.venv) $ pip install git+https://gitea.parrrate.ru/PTV/ptvp35.git
+    (venv) $ pip install git+https://gitea.parrrate.ru/PTV/ptvp35.git
 
 Basic functionality
 -------------------
diff --git a/ptvp35/__init__.py b/ptvp35/__init__.py
index 4debb14..2fd9494 100644
--- a/ptvp35/__init__.py
+++ b/ptvp35/__init__.py
@@ -65,7 +65,7 @@ note: other forms of requests will later be represented by different methods or
         raise NotImplementedError
 
     def fromline(self, line: str, /) -> tuple[Any, Any]:
-        """inverse of line(). should use free() method to construct the request.
+        """inverse of line().
 note: unstable signature."""
         raise NotImplementedError
 
@@ -87,6 +87,21 @@ note: unstable signature."""
 note: unstable signature."""
         return self.request(key, value, future=None)
 
+    def io2db(self, io: IO[str], db: dict, /) -> int:
+        """note: unstable signature."""
+        size = 0
+        for line in io:
+            self.run(line, db)
+            size += len(line)
+        return size
+
+    def db2io(self, db: dict, io: IO[str], /) -> int:
+        """note: unstable signature."""
+        size = 0
+        for key, value in db.items():
+            size += io.write(self.line(key, value))
+        return size
+
 
 class KVRequest(LineRequest):
     __slots__ = (
@@ -146,11 +161,28 @@ class TransactionRequest(LineRequest):
         self.buffer = buffer
 
 
+class DbParametres:
+    __slots__ = (
+        'path',
+        'kvfactory',
+        'buffersize',
+    )
+
+    def __init__(self, path: pathlib.Path, /, *, kvfactory: KVFactory, buffersize: int) -> None:
+        self.path = path
+        """note: unstable signature."""
+        self.kvfactory = kvfactory
+        """note: unstable signature."""
+        self.buffersize = buffersize
+        """note: unstable signature."""
+
+
 class DbConnection:
     """note: unstable constructor signature."""
 
     __slots__ = (
-        '__factory',
+        '__kvfactory',
+        '__buffersize',
         '__path',
         '__path_backup',
         '__path_recover',
@@ -181,11 +213,12 @@ class DbConnection:
 
     def __init__(
             self,
-            factory: 'DbFactory',
+            parametres: 'DbParametres',
             /
     ) -> None:
-        self.__factory = factory
-        self.__path = path = self.__factory.path
+        self.__kvfactory = parametres.kvfactory
+        self.__buffersize = parametres.buffersize
+        self.__path = path = parametres.path
         name = self.__path.name
         self.__path_backup = path.with_name(name + '.backup')
         self.__path_recover = path.with_name(name + '.recover')
@@ -212,36 +245,14 @@ class DbConnection:
     def _save_error_from_thread(self, line: str, /) -> None:
         self._queue_error(line).result()
 
-    def io2db(self, io: IO[str], db: dict, /) -> int:
-        """there are no guarantees about .error file if an error occurs here.
-note: unstable signature."""
-        size = 0
-        for line in io:
-            try:
-                self.__factory.kvfactory.run(line, db)
-                size += len(line)
-            except (json.JSONDecodeError, EOFError):
-                traceback.print_exc()
-                # this condition should never occur, but we should be able to handle this UB as best as we can
-                self._queue_error(line)
-        return size
-
-    def db2io(self, db: dict, io: IO[str], /) -> int:
-        """does not handle any errors.
-note: unstable signature."""
-        size = 0
-        for key, value in db.items():
-            size += io.write(self.__factory.kvfactory.line(key, value))
-        return size
-
     def _path2db_sync(self, path: pathlib.Path, db: dict, /) -> int:
         path.touch()
         with path.open('r') as file:
-            return self.io2db(file, db)
+            return self.__kvfactory.io2db(file, db)
 
     def _db2path_sync(self, db: dict, path: pathlib.Path, /) -> int:
         with path.open('w') as file:
-            return self.db2io(db, file)
+            return self.__kvfactory.db2io(db, file)
 
     def get(self, key: Any, default: Any, /):
         """dict-like get with mandatory default parametre."""
@@ -250,7 +261,7 @@ note: unstable signature."""
     async def set(self, key: Any, value: Any, /) -> None:
         """set the value and wait until it's written to disk."""
         future = self._create_future()
-        request = self.__factory.kvfactory.request(key, value, future=future)
+        request = self.__kvfactory.request(key, value, future=future)
         self.__mmdb[key] = value
         self.__queue.put_nowait(request)
         await future
@@ -258,7 +269,7 @@ note: unstable signature."""
     def set_nowait(self, key: Any, value: Any, /) -> None:
         """set value and add write-to-disk request to queue."""
         self.__mmdb[key] = value
-        self.__queue.put_nowait(self.__factory.kvfactory.free(key, value))
+        self.__queue.put_nowait(self.__kvfactory.free(key, value))
 
     def _clear_buffer(self, /) -> None:
         self.__buffer = StringIO()
@@ -268,9 +279,9 @@ note: unstable signature."""
     def _compress_buffer(self, /) -> StringIO:
         self.__buffer.seek(0)
         bufferdb = {}
-        self.io2db(self.__buffer, bufferdb)
+        self.__kvfactory.io2db(self.__buffer, bufferdb)
         buffer = StringIO()
-        self.db2io(bufferdb, buffer)
+        self.__kvfactory.db2io(bufferdb, buffer)
         return buffer
 
     def _dump_compressed_buffer_sync(self, /) -> None:
@@ -306,7 +317,7 @@ note: unstable signature."""
             self.__queue.put_nowait(DumpRequest(None))
 
     async def _dump_buffer_or_request_so(self, request: Request, /) -> None:
-        if self.__buffer.tell() >= self.__factory.buffersize:
+        if self.__buffer.tell() >= self.__buffersize:
             await self._dump_buffer()
             request.set_result(None)
         else:
@@ -481,10 +492,10 @@ intended for heavy tasks."""
         await self._initialize_running()
 
     @classmethod
-    async def create(cls, factory: 'DbFactory', /) -> 'DbConnection':
+    async def create(cls, parametres: 'DbParametres', /) -> 'DbConnection':
         """connect to the factory.
 note: unstable signature."""
-        dbconnection = DbConnection(factory)
+        dbconnection = DbConnection(parametres)
         await dbconnection._initialize()
         return dbconnection
 
@@ -510,22 +521,42 @@ note: unstable signature."""
         del self.__loop
         self.__not_running = True
 
-    async def complete_transaction(self, delta: dict, /) -> None:
-        """hybrid of set() and dict.update()."""
+    def _transaction_buffer(self, delta: dict, /) -> StringIO:
+        buffer = StringIO()
+        self.__kvfactory.db2io(delta, buffer)
+        self.__mmdb.update(delta)
+        return buffer
+
+    async def commit_transaction(self, delta: dict, /) -> None:
+        """hybrid of set() and dict.update().
+note: unstable signature."""
         if not delta:
             return
-        buffer = StringIO()
-        self.db2io(delta, buffer)
-        self.__mmdb.update(delta)
+        buffer = self._transaction_buffer(delta)
         future = self._create_future()
         self.__queue.put_nowait(TransactionRequest(buffer, future=future))
         await future
 
-    def submit_transaction(self, delta: dict, future: asyncio.Future | None, /) -> None:
-        """not implemented.
-low-level API.
-note: unstable (undefined) signature."""
-        raise NotImplementedError
+    def submit_transaction(self, delta: dict, /) -> None:
+        """hybrid of set_nowait() and dict.update().
+_nowait analogue of commit_transaction().
+note: this method was added only for async-sync symmetry with commit_transaction().
+note: unstable signature."""
+        if not delta:
+            return
+        buffer = self._transaction_buffer(delta)
+        self.__queue.put_nowait(TransactionRequest(buffer, future=None))
+
+    def submit_transaction_request(self, delta: dict, future: asyncio.Future | None, /) -> None:
+        """low-level API.
+for high-level synchronisation use transaction() instead.
+note: unstable signature."""
+        if not delta:
+            if future:
+                future.set_result(None)
+            return
+        buffer = self._transaction_buffer(delta)
+        self.__queue.put_nowait(TransactionRequest(buffer, future=future))
 
     async def commit(self, /) -> None:
         """wait until all requests queued before are completed."""
@@ -535,27 +566,20 @@ note: unstable (undefined) signature."""
 
     def transaction(self, /) -> 'Transaction':
         """open new transaction."""
-        return Transaction(self)
+        return Transaction(self, self.__loop)
 
 
 class DbFactory:
     __slots__ = (
-        'path',
-        'kvfactory',
-        'buffersize',
+        '__parametres',
         '__db',
     )
 
     def __init__(self, path: pathlib.Path, /, *, kvfactory: KVFactory, buffersize=1048576) -> None:
-        self.path = path
-        """note: unstable signature."""
-        self.kvfactory = kvfactory
-        """note: unstable signature."""
-        self.buffersize = buffersize
-        """note: unstable signature."""
+        self.__parametres = DbParametres(path, kvfactory=kvfactory, buffersize=buffersize)
 
     async def __aenter__(self) -> DbConnection:
-        self.__db = await DbConnection.create(self)
+        self.__db = await DbConnection.create(self.__parametres)
         return self.__db
 
     async def __aexit__(self, exc_type, exc_val, exc_tb):
@@ -570,7 +594,7 @@ class Db(DbConnection):
     def __init__(self, path: str | pathlib.Path, /, *, kvfactory: KVFactory, buffersize=1048576):
         DbConnection.__init__(
             self,
-            DbFactory(
+            DbParametres(
                 pathlib.Path(path), kvfactory=kvfactory, buffersize=buffersize
             )
         )
@@ -590,12 +614,16 @@ class TransactionView:
         '__delta',
         '__shadow',
         '__connection',
+        '__loop',
+        '__subfuture',
     )
 
-    def __init__(self, delta: dict, connection: DbConnection, /) -> None:
+    def __init__(self, delta: dict, connection: DbConnection, loop: asyncio.AbstractEventLoop, /) -> None:
         self.__delta = delta
         self.__shadow = {}
         self.__connection = connection
+        self.__loop = loop
+        self.__subfuture: asyncio.Future | None = None
 
     def get(self, key: Any, default: Any, /):
         if key in self.__delta:
@@ -605,56 +633,100 @@ class TransactionView:
         return self.__connection.get(key, default)
 
     def set_nowait(self, key: Any, value: Any, /) -> None:
+        """note: unlike the corresponding db method, this one does not catch serialisation errors early."""
         self.__delta[key] = value
 
-    async def commit(self, /) -> None:
-        """bulk analog of DbConnection.set method."""
+    def _delta(self, /) -> dict:
         delta = self.__delta.copy()
         self.__shadow |= delta
         self.__delta.clear()
-        await self.__connection.complete_transaction(delta)
+        return delta
 
-    async def commit_submitted(self, /) -> None:
-        """not implemented.
-commit previously submitted changes."""
-        raise NotImplementedError
+    async def commit(self, /) -> None:
+        """bulk analogue of DbConnection.set()."""
+        subfuture: asyncio.Future | None = self.__subfuture
+        self.__subfuture = None
+        delta = self._delta()
+        await self.__connection.commit_transaction(delta)
+        if subfuture is not None:
+            await subfuture
 
     def submit(self, /) -> None:
-        """not implemented.
-submit changes.
-_nowait analog of commit.
-bulk analog of DbConnection.set_nowait method."""
-        raise NotImplementedError
+        """submit changes.
+_nowait analogue of commit().
+bulk analogue of DbConnection.set_nowait()."""
+        delta = self._delta()
+        future = self.__loop.create_future()
+        self.__connection.submit_transaction_request(delta, future)
+        self.__subfuture = self._gather(self.__subfuture, future)
+
+    def _do_gather(self, left: asyncio.Future, right: asyncio.Future) -> asyncio.Future:
+        future = self.__loop.create_future()
+
+        def rcallback(fr: asyncio.Future) -> None:
+            if (e := fr.exception()) is not None:
+                future.set_exception(e)
+            else:
+                future.set_result(None)
+
+        def lcallback(fl: asyncio.Future) -> None:
+            if (e := fl.exception()) is not None:
+                future.set_exception(e)
+            else:
+                right.add_done_callback(rcallback)
+
+        left.add_done_callback(lcallback)
+
+        return future
+
+    def _gather(self, left: asyncio.Future | None, right: asyncio.Future | None) -> asyncio.Future | None:
+        match (left, right):
+            case None, _:
+                return right
+            case _, None:
+                return left
+            case asyncio.Future() as fl, asyncio.Future() as fr:
+                return self._do_gather(fl, fr)
+            case _:
+                raise TypeError
 
 
 class Transaction:
-    """note: unstable signature.
-note: synchronous with is not implemented."""
+    """note: unstable signature."""
 
     __slots__ = (
         '__connection',
-        '__delta',
+        '__loop',
+        '__view',
+        '__running',
     )
 
-    __delta: dict
+    __view: TransactionView
 
-    def __init__(self, connection: DbConnection, /) -> None:
+    def __init__(self, connection: DbConnection, loop: asyncio.AbstractEventLoop, /) -> None:
         self.__connection = connection
+        self.__loop = loop
+        self.__running = False
 
     async def __aenter__(self) -> TransactionView:
-        self.__delta = {}
-        return TransactionView(self.__delta, self.__connection)
+        return self.__enter__()
 
     async def __aexit__(self, exc_type, exc_val, exc_tb):
         if exc_type is None:
-            await self.__connection.complete_transaction(self.__delta)
-        del self.__delta
+            await self.__view.commit()
+        self._clean()
+
+    def _clean(self, /) -> None:
+        del self.__view
+        self.__running = False
 
     def __enter__(self) -> TransactionView:
-        self.__delta = {}
-        return TransactionView(self.__delta, self.__connection)
+        assert not self.__running
+        self.__running = True
+        self.__view = TransactionView({}, self.__connection, self.__loop)
+        return self.__view
 
     def __exit__(self, exc_type, exc_val, exc_tb):
         if exc_type is None:
-            self.__connection.submit_transaction(self.__delta, None)
-        del self.__delta
+            self.__view.submit()
+        self._clean()
diff --git a/setup.py b/setup.py
index befcfa9..eab54e4 100644
--- a/setup.py
+++ b/setup.py
@@ -2,7 +2,7 @@ from setuptools import setup
 
 setup(
     name='ptvp35',
-    version='1.0rc3',
+    version='1.0rc4',
     packages=['ptvp35'],
     url='https://gitea.ongoteam.net/PTV/ptvp35',
     license='',