diff --git a/Telegram/SourceFiles/mtproto/connection.cpp b/Telegram/SourceFiles/mtproto/connection.cpp
index 6cef04aed..e21f8df16 100644
--- a/Telegram/SourceFiles/mtproto/connection.cpp
+++ b/Telegram/SourceFiles/mtproto/connection.cpp
@@ -291,11 +291,15 @@ QString ConnectionPrivate::transport() const {
 bool ConnectionPrivate::setState(int32 state, int32 ifState) {
 	if (ifState != Connection::UpdateAlways) {
 		QReadLocker lock(&stateConnMutex);
-		if (_state != ifState) return false;
+		if (_state != ifState) {
+			return false;
+		}
 	}
 
 	QWriteLocker lock(&stateConnMutex);
-	if (_state == state) return false;
+	if (_state == state) {
+		return false;
+	}
 	_state = state;
 	if (state < 0) {
 		_retryTimeout = -state;
@@ -308,118 +312,14 @@ bool ConnectionPrivate::setState(int32 state, int32 ifState) {
 	return true;
 }
 
-void ConnectionPrivate::resetSession() { // recreate all msg_id and msg_seqno
+void ConnectionPrivate::resetSession() {
+	MTP_LOG(_shiftedDcId, ("Resetting session!"));
 	_needSessionReset = false;
 
-	MTP_LOG(_shiftedDcId, ("Resetting session!"));
-
-	QWriteLocker locker1(_sessionData->haveSentMutex());
-	QWriteLocker locker2(_sessionData->toResendMutex());
-	QWriteLocker locker3(_sessionData->toSendMutex());
-	QWriteLocker locker4(_sessionData->wereAckedMutex());
-	auto &haveSent = _sessionData->haveSentMap();
-	auto &toResend = _sessionData->toResendMap();
-	auto &toSend = _sessionData->toSendMap();
-	auto &wereAcked = _sessionData->wereAckedMap();
-
-	auto newId = base::unixtime::mtproto_msg_id();
-	auto setSeqNumbers = RequestMap();
-	auto replaces = QMap<mtpMsgId, mtpMsgId>();
-	for (auto i = haveSent.cbegin(), e = haveSent.cend(); i != e; ++i) {
-		if (!i.value().isSentContainer()) {
-			if (!*(mtpMsgId*)(i.value()->constData() + 4)) continue;
-
-			mtpMsgId id = i.key();
-			if (id > newId) {
-				while (toResend.constFind(newId) != toResend.cend()
-					|| wereAcked.constFind(newId) != wereAcked.cend()
-					|| haveSent.constFind(newId) != haveSent.cend()) {
-					newId = base::unixtime::mtproto_msg_id();
-				}
-
-				MTP_LOG(_shiftedDcId, ("Replacing msgId %1 to %2!"
-					).arg(id
-					).arg(newId));
-				replaces.insert(id, newId);
-				id = newId;
-				*(mtpMsgId*)(i.value()->data() + 4) = id;
-			}
-			setSeqNumbers.insert(id, i.value());
-		}
-	}
-	// Collect all non-container requests.
-	for (auto i = toResend.cbegin(), e = toResend.cend(); i != e; ++i) {
-		const auto j = toSend.constFind(i.value());
-		if (j == toSend.cend()) continue;
-
-		if (!j.value().isSentContainer()) {
-			if (!*(mtpMsgId*)(j.value()->constData() + 4)) continue;
-
-			mtpMsgId id = i.key();
-			if (id > newId) {
-				while (toResend.constFind(newId) != toResend.cend()
-					|| wereAcked.constFind(newId) != wereAcked.cend()
-					|| haveSent.constFind(newId) != haveSent.cend()) {
-					newId = base::unixtime::mtproto_msg_id();
-				}
-
-				MTP_LOG(_shiftedDcId, ("Replacing msgId %1 to %2!"
-					).arg(id
-					).arg(newId));
-				replaces.insert(id, newId);
-				id = newId;
-				*(mtpMsgId*)(j.value()->data() + 4) = id;
-			}
-			setSeqNumbers.insert(id, j.value());
-		}
-	}
-
-	const auto sessionId = rand_value<uint64>();
-	DEBUG_LOG(("MTP Info: creating new session after bad_msg_notification, setting random server_session %1").arg(sessionId));
-	_sessionData->setSessionId(sessionId);
-
-	for (auto i = setSeqNumbers.cbegin(), e = setSeqNumbers.cend(); i != e; ++i) { // generate new seq_numbers
-		bool wasNeedAck = (*(i.value()->data() + 6) & 1);
-		*(i.value()->data() + 6) = _sessionData->nextRequestSeqNumber(wasNeedAck);
-	}
-	if (!replaces.isEmpty()) {
-		for (auto i = replaces.cbegin(), e = replaces.cend(); i != e; ++i) { // replace msgIds keys in all data structs
-			const auto j = haveSent.find(i.key());
-			if (j != haveSent.cend()) {
-				const auto req = j.value();
-				haveSent.erase(j);
-				haveSent.insert(i.value(), req);
-			}
-			const auto k = toResend.find(i.key());
-			if (k != toResend.cend()) {
-				const auto req = k.value();
-				toResend.erase(k);
-				toResend.insert(i.value(), req);
-			}
-			const auto l = wereAcked.find(i.key());
-			if (l != wereAcked.cend()) {
-				DEBUG_LOG(("MTP Info: Replaced %1 with %2 in wereAcked."
-					).arg(i.key()
-					).arg(i.value()));
-
-				const auto req = l.value();
-				wereAcked.erase(l);
-				wereAcked.insert(i.value(), req);
-			}
-		}
-		for (auto i = haveSent.cbegin(), e = haveSent.cend(); i != e; ++i) { // replace msgIds in saved containers
-			if (i.value().isSentContainer()) {
-				mtpMsgId *ids = (mtpMsgId*)(i.value()->data() + 8);
-				for (uint32 j = 0, l = (i.value()->size() - 8) >> 1; j < l; ++j) {
-					const auto k = replaces.constFind(ids[j]);
-					if (k != replaces.cend()) {
-						ids[j] = k.value();
-					}
-				}
-			}
-		}
-	}
+	DEBUG_LOG(("MTP Info: creating new session in resetSession."));
+	_sessionData->changeSessionId();
 
+	// #TODO move to sessionData, clear on changeSessionIdLocked.
 	_ackRequestData.clear();
 	_resendRequestData.clear();
 	{
@@ -432,93 +332,99 @@ void ConnectionPrivate::resetSession() { // recreate all msg_id and msg_seqno
 
 mtpMsgId ConnectionPrivate::prepareToSend(
 		SecureRequest &request,
-		mtpMsgId currentLastId) {
-	if (request->size() < 9) {
-		return 0;
-	}
+		mtpMsgId currentLastId,
+		bool forceNewMsgId) {
+	Expects(request->size() > 8);
+
 	if (const auto msgId = request.getMsgId()) {
 		// resending this request
-		QWriteLocker locker(_sessionData->toResendMutex());
+		QWriteLocker lock(_sessionData->toResendMutex());
 		auto &toResend = _sessionData->toResendMap();
 		const auto i = toResend.find(msgId);
 		if (i != toResend.cend()) {
 			toResend.erase(i);
 		}
-		return msgId;
+		lock.unlock();
+
+		return (forceNewMsgId || msgId > currentLastId)
+			? replaceMsgId(request, currentLastId)
+			: msgId;
 	}
 	request.setMsgId(currentLastId);
 	request.setSeqNo(_sessionData->nextRequestSeqNumber(request.needAck()));
+	if (request->requestId) {
+		MTP_LOG(_shiftedDcId, ("[r%1] msg_id 0 -> %2").arg(request->requestId).arg(currentLastId));
+	}
 	return currentLastId;
 }
 
 mtpMsgId ConnectionPrivate::replaceMsgId(SecureRequest &request, mtpMsgId newId) {
-	if (request->size() < 9) return 0;
+	Expects(request->size() > 8);
 
 	const auto oldMsgId = request.getMsgId();
-	if (oldMsgId != newId) {
-		if (oldMsgId) {
-			QWriteLocker locker(_sessionData->toResendMutex());
-			// haveSentMutex() and wereAckedMutex() were locked in tryToSend()
-
-			auto &toResend = _sessionData->toResendMap();
-			auto &wereAcked = _sessionData->wereAckedMap();
-			auto &haveSent = _sessionData->haveSentMap();
-
-			while (true) {
-				if (toResend.constFind(newId) == toResend.cend() && wereAcked.constFind(newId) == wereAcked.cend() && haveSent.constFind(newId) == haveSent.cend()) {
-					break;
-				}
-				const auto m = base::unixtime::mtproto_msg_id();
-				if (m <= newId) break; // wtf
-
-				newId = m;
-			}
-
-			const auto i = toResend.find(oldMsgId);
-			if (i != toResend.cend()) {
-				const auto req = i.value();
-				toResend.erase(i);
-				toResend.insert(newId, req);
-			}
-
-			const auto j = wereAcked.find(oldMsgId);
-			if (j != wereAcked.cend()) {
-				const auto req = j.value();
-				wereAcked.erase(j);
-				wereAcked.insert(newId, req);
-			}
-
-			const auto k = haveSent.find(oldMsgId);
-			if (k != haveSent.cend()) {
-				const auto req = k.value();
-				haveSent.erase(k);
-				haveSent.insert(newId, req);
-			}
-
-			for (auto l = haveSent.begin(); l != haveSent.cend(); ++l) {
-				const auto req = l.value();
-				if (req.isSentContainer()) {
-					const auto ids = (mtpMsgId *)(req->data() + 8);
-					for (uint32 i = 0, l = (req->size() - 8) >> 1; i < l; ++i) {
-						if (ids[i] == oldMsgId) {
-							ids[i] = newId;
-						}
-					}
-				}
-			}
-		} else {
-			request.setSeqNo(_sessionData->nextRequestSeqNumber(request.needAck()));
-		}
-		request.setMsgId(newId);
+	if (oldMsgId == newId) {
+		return newId;
 	}
+	QWriteLocker locker(_sessionData->toResendMutex());
+	// haveSentMutex() and wereAckedMutex() were locked in tryToSend()
+
+	auto &toResend = _sessionData->toResendMap();
+	auto &wereAcked = _sessionData->wereAckedMap();
+	auto &haveSent = _sessionData->haveSentMap();
+
+	while (toResend.constFind(newId) != toResend.cend()
+		|| wereAcked.constFind(newId) != wereAcked.cend()
+		|| haveSent.constFind(newId) != haveSent.cend()) {
+		newId = base::unixtime::mtproto_msg_id();
+	}
+
+	MTP_LOG(_shiftedDcId, ("[r%1] msg_id %2 -> %3").arg(request->requestId).arg(oldMsgId).arg(newId));
+
+	const auto i = toResend.find(oldMsgId);
+	if (i != toResend.cend()) {
+		const auto req = i.value();
+		toResend.erase(i);
+		toResend.insert(newId, req);
+	}
+
+	const auto j = wereAcked.find(oldMsgId);
+	if (j != wereAcked.cend()) {
+		const auto req = j.value();
+		wereAcked.erase(j);
+		wereAcked.insert(newId, req);
+	}
+
+	const auto k = haveSent.find(oldMsgId);
+	if (k != haveSent.cend()) {
+		const auto req = k.value();
+		haveSent.erase(k);
+		haveSent.insert(newId, req);
+	}
+
+	for (auto l = haveSent.begin(); l != haveSent.cend(); ++l) {
+		const auto req = l.value();
+		if (req.isSentContainer()) {
+			const auto ids = (mtpMsgId *)(req->data() + 8);
+			for (uint32 i = 0, l = (req->size() - 8) >> 1; i < l; ++i) {
+				if (ids[i] == oldMsgId) {
+					ids[i] = newId;
+				}
+			}
+		}
+	}
+
+	request.setMsgId(newId);
+	request.setSeqNo(_sessionData->nextRequestSeqNumber(request.needAck()));
 	return newId;
 }
 
-mtpMsgId ConnectionPrivate::placeToContainer(SecureRequest &toSendRequest, mtpMsgId &bigMsgId, mtpMsgId *&haveSentArr, SecureRequest &req) {
-	auto msgId = prepareToSend(req, bigMsgId);
-	if (msgId > bigMsgId) {
-		msgId = replaceMsgId(req, bigMsgId);
-	}
+mtpMsgId ConnectionPrivate::placeToContainer(
+		SecureRequest &toSendRequest,
+		mtpMsgId &bigMsgId,
+		bool forceNewMsgId,
+		mtpMsgId *&haveSentArr,
+		SecureRequest &req) {
+	const auto msgId = prepareToSend(req, bigMsgId, forceNewMsgId);
 	if (msgId >= bigMsgId) {
 		bigMsgId = base::unixtime::mtproto_msg_id();
 	}
@@ -551,7 +457,12 @@ void ConnectionPrivate::tryToSend() {
 		&& _pingSendAt <= crl::now()) {
 		_pingIdToSend = openssl::RandomValue<mtpPingId>();
 	}
+	const auto forceNewMsgId = sendAll
+		&& _sessionData->markSessionAsStarted();
 
+	if (forceNewMsgId) {
+		int a = 0;
+	}
 	auto pingRequest = SecureRequest();
 	auto ackRequest = SecureRequest();
 	auto resendRequest = SecureRequest();
@@ -744,7 +655,8 @@ void ConnectionPrivate::tryToSend() {
 
 			const auto msgId = prepareToSend(
 				toSendRequest,
-				base::unixtime::mtproto_msg_id());
+				base::unixtime::mtproto_msg_id(),
+				forceNewMsgId);
 			if (pingRequest) {
 				_pingMsgId = msgId;
 				needAnyResponse = true;
@@ -839,17 +751,22 @@ void ConnectionPrivate::tryToSend() {
 			auto haveSentArr = (mtpMsgId*)(haveSentIdsWrap->data() + 8);
 
 			if (pingRequest) {
-				_pingMsgId = placeToContainer(toSendRequest, bigMsgId, haveSentArr, pingRequest);
+				_pingMsgId = placeToContainer(
+					toSendRequest,
+					bigMsgId,
+					forceNewMsgId,
+					haveSentArr,
+					pingRequest);
 				needAnyResponse = true;
 			} else if (resendRequest || stateRequest || bindDcKeyRequest) {
 				needAnyResponse = true;
 			}
 			for (auto i = toSend.begin(), e = toSend.end(); i != e; ++i) {
 				auto &req = i.value();
-				auto msgId = prepareToSend(req, bigMsgId);
-				if (msgId > bigMsgId) {
-					msgId = replaceMsgId(req, bigMsgId);
-				}
+				const auto msgId = prepareToSend(
+					req,
+					bigMsgId,
+					forceNewMsgId);
 				if (msgId >= bigMsgId) {
 					bigMsgId = base::unixtime::mtproto_msg_id();
 				}
@@ -889,21 +806,24 @@ void ConnectionPrivate::tryToSend() {
 				}
 			}
 			if (stateRequest) {
-				mtpMsgId msgId = placeToContainer(toSendRequest, bigMsgId, haveSentArr, stateRequest);
+				mtpMsgId msgId = placeToContainer(toSendRequest, bigMsgId, forceNewMsgId, haveSentArr, stateRequest);
 				stateRequest->msDate = 0; // 0 for state request, do not request state of it
 				Assert(!haveSent.contains(msgId));
 				haveSent.insert(msgId, stateRequest);
 			}
-			if (resendRequest) placeToContainer(toSendRequest, bigMsgId, haveSentArr, resendRequest);
-			if (ackRequest) placeToContainer(toSendRequest, bigMsgId, haveSentArr, ackRequest);
-			if (httpWaitRequest) placeToContainer(toSendRequest, bigMsgId, haveSentArr, httpWaitRequest);
-			if (bindDcKeyRequest) placeToContainer(toSendRequest, bigMsgId, haveSentArr, bindDcKeyRequest);
+			if (resendRequest) placeToContainer(toSendRequest, bigMsgId, forceNewMsgId, haveSentArr, resendRequest);
+			if (ackRequest) placeToContainer(toSendRequest, bigMsgId, forceNewMsgId, haveSentArr, ackRequest);
+			if (httpWaitRequest) placeToContainer(toSendRequest, bigMsgId, forceNewMsgId, haveSentArr, httpWaitRequest);
+			if (bindDcKeyRequest) placeToContainer(toSendRequest, bigMsgId, forceNewMsgId, haveSentArr, bindDcKeyRequest);
 
-			mtpMsgId contMsgId = prepareToSend(toSendRequest, bigMsgId);
-			*(mtpMsgId*)(haveSentIdsWrap->data() + 4) = contMsgId;
+			const auto containerMsgId = prepareToSend(
+				toSendRequest,
+				bigMsgId,
+				forceNewMsgId);
+			*(mtpMsgId*)(haveSentIdsWrap->data() + 4) = containerMsgId;
 			(*haveSentIdsWrap)[6] = 0; // for container, msDate = 0, seqNo = 0
-			Assert(!haveSent.contains(contMsgId));
-			haveSent.insert(contMsgId, haveSentIdsWrap);
+			Assert(!haveSent.contains(containerMsgId));
+			haveSent.insert(containerMsgId, haveSentIdsWrap);
 			toSend.clear();
 		}
 	}
@@ -1050,7 +970,6 @@ void ConnectionPrivate::restart() {
 	if (_needSessionReset) {
 		resetSession();
 	}
-	_restarted = true;
 	if (_retryTimer.isActive()) {
 		return;
 	}
@@ -1144,7 +1063,6 @@ void ConnectionPrivate::waitReceivedFailed() {
 		_waitForReceived *= 2;
 	}
 	doDisconnect();
-	_restarted = true;
 	if (_retryTimer.isActive()) {
 		return;
 	}
@@ -1164,7 +1082,6 @@ void ConnectionPrivate::waitConnectedFailed() {
 	}
 
 	connectingTimedOut();
-	_restarted = true;
 
 	DEBUG_LOG(("MTP Info: immediate restart!"));
 	InvokeQueued(this, [=] { connectToServer(); });
@@ -1183,9 +1100,7 @@ void ConnectionPrivate::connectingTimedOut() {
 
 void ConnectionPrivate::doDisconnect() {
 	destroyAllConnections();
-
 	setState(DisconnectedState);
-	_restarted = false;
 }
 
 void ConnectionPrivate::finishAndDestroy() {
@@ -1212,6 +1127,8 @@ void ConnectionPrivate::requestCDNConfig() {
 }
 
 void ConnectionPrivate::handleReceived() {
+	Expects(_temporaryKey != nullptr);
+
 	onReceivedSome();
 
 	while (!_connection->received().empty()) {
@@ -1345,9 +1262,8 @@ void ConnectionPrivate::handleReceived() {
 				DEBUG_LOG(("MTP Info: other salt received... received: %1, my salt: %2, updating...").arg(serverSalt).arg(mySalt));
 				_sessionData->setSalt(serverSalt);
 
-				if (setState(ConnectedState, ConnectingState) && _restarted) {
-					_sessionData->queueResendAll();
-					_restarted = false;
+				if (setState(ConnectedState, ConnectingState)) {
+					_sessionData->resendAll();
 				}
 			} else {
 				DEBUG_LOG(("MTP Info: other salt received... received: %1, my salt: %2").arg(serverSalt).arg(mySalt));
@@ -1393,9 +1309,10 @@ void ConnectionPrivate::handleReceived() {
 		}
 
 		if (res != HandleResult::Success && res != HandleResult::Ignored) {
-			_needSessionReset = (res == HandleResult::ResetSession);
 			if (res == HandleResult::DestroyTemporaryKey) {
 				destroyTemporaryKey();
+			} else if (res == HandleResult::ResetSession) {
+				_needSessionReset = true;
 			}
 			return restart();
 		}
@@ -1633,11 +1550,8 @@ ConnectionPrivate::HandleResult ConnectionPrivate::handleOneReceived(const mtpPr
 		_sessionData->setSalt(serverSalt);
 		base::unixtime::update(serverTime);
 
-		if (setState(ConnectedState, ConnectingState)) { // maybe only connected
-			if (_restarted) {
-				_sessionData->queueResendAll();
-				_restarted = false;
-			}
+		if (setState(ConnectedState, ConnectingState)) {
+			_sessionData->resendAll();
 		}
 
 		badTime = false;
@@ -1863,7 +1777,6 @@ ConnectionPrivate::HandleResult ConnectionPrivate::handleOneReceived(const mtpPr
 				return HandleResult::Ignored;
 			}
 		}
-		requestsAcked(ids, true);
 
 		if (typeId == mtpc_gzip_packed) {
 			DEBUG_LOG(("RPC Info: gzip container"));
@@ -1880,12 +1793,13 @@ ConnectionPrivate::HandleResult ConnectionPrivate::handleOneReceived(const mtpPr
 			if (DcKeyBinder::IsDestroyedTemporaryKeyError(response)) {
 				return HandleResult::DestroyTemporaryKey;
 			}
-		} else {
 			// An error could be some RPC_CALL_FAIL or other error inside
 			// the initConnection, so we're not sure yet that it was inited.
 			// Wait till a good response is received.
+		} else {
 			_sessionData->notifyConnectionInited(*_connectionOptions);
 		}
+		requestsAcked(ids, true);
 
 		if (_keyBinder) {
 			const auto result = _keyBinder->handleResponse(
@@ -1945,11 +1859,16 @@ ConnectionPrivate::HandleResult ConnectionPrivate::handleOneReceived(const mtpPr
 			const auto &haveSent = _sessionData->haveSentMap();
 			toResend.reserve(haveSent.size());
 			for (auto i = haveSent.cbegin(), e = haveSent.cend(); i != e; ++i) {
-				if (i.key() >= firstMsgId) break;
-				if (i.value()->requestId) toResend.push_back(i.key());
+				if (i.key() >= firstMsgId) {
+					break;
+				} else if (i.value()->requestId) {
+					toResend.push_back(i.key());
+				}
 			}
 		}
-		resendMany(toResend, 10, true);
+		for (const auto msgId : toResend) {
+			_sessionData->resend(msgId, 10, true);
+		}
 
 		mtpBuffer update(from - start);
 		if (from > start) memcpy(update.data(), start, (from - start) * sizeof(mtpPrime));
@@ -2237,26 +2156,18 @@ void ConnectionPrivate::resend(
 		mtpMsgId msgId,
 		crl::time msCanWait,
 		bool forceContainer) {
-	if (msgId == _pingMsgId) {
-		return;
+	if (msgId != _pingMsgId) {
+		_sessionData->resend(msgId, msCanWait, forceContainer);
 	}
-	_sessionData->queueResend(msgId, msCanWait, forceContainer);
 }
 
 void ConnectionPrivate::resendMany(
 		QVector<mtpMsgId> msgIds,
 		crl::time msCanWait,
 		bool forceContainer) {
-	for (int32 i = 0, l = msgIds.size(); i < l; ++i) {
-		if (msgIds.at(i) == _pingMsgId) {
-			msgIds.remove(i);
-			--l;
-		}
+	for (const auto msgId : msgIds) {
+		resend(msgId, msCanWait, forceContainer);
 	}
-	_sessionData->queueResendMany(
-		std::move(msgIds),
-		msCanWait,
-		forceContainer);
 }
 
 void ConnectionPrivate::onConnected(
@@ -2340,10 +2251,13 @@ void ConnectionPrivate::removeTestConnection(
 }
 
 void ConnectionPrivate::checkAuthKey() {
-	if (!_keyId) {
-		updateAuthKey();
-	} else {
+	Expects(_keyCreator == nullptr);
+	Expects(_keyBinder == nullptr || _keyId != 0);
+
+	if (_keyId) {
 		authKeyChecked();
+	} else {
+		applyAuthKey(_sessionData->getTemporaryKey());
 	}
 }
 
@@ -2359,23 +2273,40 @@ void ConnectionPrivate::updateAuthKey() {
 void ConnectionPrivate::applyAuthKey(AuthKeyPtr &&temporaryKey) {
 	_temporaryKey = std::move(temporaryKey);
 	const auto newKeyId = _temporaryKey ? _temporaryKey->keyId() : 0;
-	if (newKeyId) {
+	if (_keyId) {
 		if (_keyId == newKeyId) {
 			return;
 		}
-		_sessionData->setCurrentKeyId(newKeyId);
+		_keyId = 0;
+		if (_sessionData->setCurrentKeyId(_keyId)) {
+			_ackRequestData.clear(); // #TODO move to sessionData.
+			_resendRequestData.clear();
+			{
+				QWriteLocker locker5(_sessionData->stateRequestMutex());
+				_sessionData->stateRequestMap().clear();
+			}
+		}
+		DEBUG_LOG(("MTP Error: auth_key id for dc %1 changed, restarting..."
+			).arg(_shiftedDcId));
+		if (_connection) {
+			restart();
+		}
+		return;
 	}
-	_keyId = newKeyId;
 	if (!_connection) {
 		return;
 	}
-	if (const auto already = _connection->sentEncryptedWithKeyId()) {
-		Assert(already != newKeyId);
-		DEBUG_LOG(("MTP Error: auth_key id for dc %1 changed").arg(_shiftedDcId));
-
-		restart();
-		return;
+	if (newKeyId && _sessionData->setCurrentKeyId(newKeyId)) {
+		_ackRequestData.clear(); // #TODO move to sessionData.
+		_resendRequestData.clear();
+		{
+			QWriteLocker locker5(_sessionData->stateRequestMutex());
+			_sessionData->stateRequestMap().clear();
+		}
 	}
+	_keyId = newKeyId;
+	Assert(!_connection->sentEncryptedWithKeyId());
+
 	DEBUG_LOG(("AuthKey Info: Connection update key from Session, dc %1 result: %2").arg(_shiftedDcId).arg(Logs::mb(&_keyId, sizeof(_keyId)).str()));
 	if (_keyId) {
 		return authKeyChecked();
@@ -2470,12 +2401,8 @@ void ConnectionPrivate::authKeyChecked() {
 		handleReceived();
 	});
 
-	if (_sessionData->getSalt()) {
-		setState(ConnectedState);
-		if (_restarted) {
-			_sessionData->queueResendAll();
-			_restarted = false;
-		}
+	if (_sessionData->getSalt() && setState(ConnectedState)) {
+		_sessionData->resendAll();
 	} // else receive salt in bad_server_salt first, then try to send all the requests
 
 	_pingIdToSend = rand_value<uint64>(); // get server_salt
@@ -2525,7 +2452,6 @@ void ConnectionPrivate::destroyTemporaryKey() {
 	if (_temporaryKey) {
 		_sessionData->destroyTemporaryKey(_temporaryKey->keyId());
 	}
-	_needSessionReset = true;
 	applyAuthKey(nullptr);
 }
 
diff --git a/Telegram/SourceFiles/mtproto/connection.h b/Telegram/SourceFiles/mtproto/connection.h
index 1aa3ae376..d786f80ea 100644
--- a/Telegram/SourceFiles/mtproto/connection.h
+++ b/Telegram/SourceFiles/mtproto/connection.h
@@ -139,9 +139,13 @@ private:
 	mtpMsgId placeToContainer(
 		SecureRequest &toSendRequest,
 		mtpMsgId &bigMsgId,
+		bool forceNewMsgId,
 		mtpMsgId *&haveSentArr,
 		SecureRequest &req);
-	mtpMsgId prepareToSend(SecureRequest &request, mtpMsgId currentLastId);
+	mtpMsgId prepareToSend(
+		SecureRequest &request,
+		mtpMsgId currentLastId,
+		bool forceNewMsgId);
 	mtpMsgId replaceMsgId(SecureRequest &request, mtpMsgId newId);
 
 	bool sendSecureRequest(SecureRequest &&request, bool needAnyResponse);
@@ -221,7 +225,6 @@ private:
 	mtpMsgId _pingMsgId = 0;
 	base::Timer _pingSender;
 
-	bool _restarted = false;
 	bool _finished = false;
 
 	AuthKeyPtr _temporaryKey;
diff --git a/Telegram/SourceFiles/mtproto/mtp_instance.cpp b/Telegram/SourceFiles/mtproto/mtp_instance.cpp
index 0f73de8da..f4c0a22e9 100644
--- a/Telegram/SourceFiles/mtproto/mtp_instance.cpp
+++ b/Telegram/SourceFiles/mtproto/mtp_instance.cpp
@@ -1156,7 +1156,9 @@ void Instance::Private::onSessionReset(ShiftedDcId dcWithShift) {
 
 bool Instance::Private::rpcErrorOccured(mtpRequestId requestId, const RPCFailHandlerPtr &onFail, const RPCError &err) { // return true if need to clean request data
 	if (isDefaultHandledError(err)) {
-		if (onFail && (*onFail)(requestId, err)) return true;
+		if (onFail && (*onFail)(requestId, err)) {
+			return true;
+		}
 	}
 
 	if (onErrorDefault(requestId, err)) {
diff --git a/Telegram/SourceFiles/mtproto/session.cpp b/Telegram/SourceFiles/mtproto/session.cpp
index 38f3586c8..0504cb045 100644
--- a/Telegram/SourceFiles/mtproto/session.cpp
+++ b/Telegram/SourceFiles/mtproto/session.cpp
@@ -26,10 +26,6 @@ constexpr auto kCheckResendTimeout = crl::time(10000);
 // when resending request or checking its state.
 constexpr auto kCheckResendWaiting = crl::time(1000);
 
-// How much ints should message contain for us not to resend,
-// but instead to check its state.
-constexpr auto kResendThreshold = 1;
-
 // Container lives 10 minutes in haveSent map.
 constexpr auto kContainerLives = 600;
 
@@ -76,15 +72,51 @@ void SessionData::withSession(Callback &&callback) {
 	}
 }
 
-void SessionData::setCurrentKeyId(uint64 keyId) {
+bool SessionData::setCurrentKeyId(uint64 keyId) {
 	QWriteLocker locker(&_lock);
 	if (_keyId == keyId) {
-		return;
+		return false;
 	}
 	_keyId = keyId;
-	_sessionId = openssl::RandomValue<uint64>();
+
+	DEBUG_LOG(("MTP Info: auth key set in SessionData, id %1").arg(keyId));
+
+	changeSessionIdLocked();
+	return true;
+}
+
+void SessionData::changeSessionId() {
+	QWriteLocker locker(&_lock);
+	changeSessionIdLocked();
+}
+
+void SessionData::changeSessionIdLocked() {
+	auto sessionId = _sessionId;
+	do {
+		sessionId = openssl::RandomValue<uint64>();
+	} while (_sessionId == sessionId);
+
+	DEBUG_LOG(("MTP Info: setting server_session: %1").arg(sessionId));
+
+	_sessionId = sessionId;
 	_messagesSent = 0;
-	DEBUG_LOG(("MTP Info: new auth key set in SessionData, id %1, setting random server_session %2").arg(_keyId).arg(_sessionId));
+	_sessionMarkedAsStarted = false;
+}
+
+uint32 SessionData::nextRequestSeqNumber(bool needAck) {
+	QWriteLocker locker(&_lock);
+	auto result = _messagesSent;
+	_messagesSent += (needAck ? 1 : 0);
+	return result * 2 + (needAck ? 1 : 0);
+}
+
+bool SessionData::markSessionAsStarted() {
+	QWriteLocker locker(&_lock);
+	if (_sessionMarkedAsStarted) {
+		return false;
+	}
+	_sessionMarkedAsStarted = true;
+	return true;
 }
 
 void SessionData::setKeyForCheck(const AuthKeyPtr &key) {
@@ -166,12 +198,6 @@ void SessionData::queueConnectionStateChange(int newState) {
 	});
 }
 
-void SessionData::queueResendAll() {
-	withSession([](not_null<Session*> session) {
-		session->resendAll();
-	});
-}
-
 void SessionData::queueResetDone() {
 	withSession([](not_null<Session*> session) {
 		session->resetDone();
@@ -190,24 +216,21 @@ void SessionData::queueSendMsgsStateInfo(quint64 msgId, QByteArray data) {
 	});
 }
 
-void SessionData::queueResend(
+void SessionData::resend(
 		mtpMsgId msgId,
 		crl::time msCanWait,
 		bool forceContainer) {
-	withSession([=](not_null<Session*> session) {
-		session->resend(msgId, msCanWait, forceContainer);
-	});
+	QMutexLocker lock(&_ownerMutex);
+	if (_owner) {
+		_owner->resend(msgId, msCanWait, forceContainer);
+	}
 }
 
-void SessionData::queueResendMany(
-		QVector<mtpMsgId> msgIds,
-		crl::time msCanWait,
-		bool forceContainer) {
-	withSession([=](not_null<Session*> session) {
-		for (const auto msgId : msgIds) {
-			session->resend(msgId, msCanWait, forceContainer);
-		}
-	});
+void SessionData::resendAll() {
+	QMutexLocker lock(&_ownerMutex);
+	if (_owner) {
+		_owner->resendAll();
+	}
 }
 
 bool SessionData::connectionInited() const {
@@ -437,7 +460,6 @@ bool Session::sharedDc() const {
 }
 
 void Session::checkRequestsByTimer() {
-	QVector<mtpMsgId> resendingIds;
 	QVector<mtpMsgId> removingIds; // remove very old (10 minutes) containers and resend requests
 	QVector<mtpMsgId> stateRequestIds;
 
@@ -450,14 +472,9 @@ void Session::checkRequestsByTimer() {
 			auto &req = i.value();
 			if (req->msDate > 0) {
 				if (req->msDate + kCheckResendTimeout < ms) { // need to resend or check state
-					if (req.messageSize() < kResendThreshold) { // resend
-						resendingIds.reserve(haveSentCount);
-						resendingIds.push_back(i.key());
-					} else {
-						req->msDate = ms;
-						stateRequestIds.reserve(haveSentCount);
-						stateRequestIds.push_back(i.key());
-					}
+					req->msDate = ms;
+					stateRequestIds.reserve(haveSentCount);
+					stateRequestIds.push_back(i.key());
 				}
 			} else if (base::unixtime::now()
 					> int32(i.key() >> 32) + kContainerLives) {
@@ -477,12 +494,6 @@ void Session::checkRequestsByTimer() {
 		}
 		sendAnything(kCheckResendWaiting);
 	}
-	if (!resendingIds.isEmpty()) {
-		for (uint32 i = 0, l = resendingIds.size(); i < l; ++i) {
-			DEBUG_LOG(("MTP Info: resending request %1").arg(resendingIds[i]));
-			resend(resendingIds[i], kCheckResendWaiting);
-		}
-	}
 	if (!removingIds.isEmpty()) {
 		auto clearCallbacks = std::vector<RPCCallbackClear>();
 		{
@@ -586,40 +597,35 @@ QString Session::transport() const {
 	return _connection ? _connection->transport() : QString();
 }
 
-mtpRequestId Session::resend(
+void Session::resend(
 		mtpMsgId msgId,
 		crl::time msCanWait,
 		bool forceContainer) {
-	SecureRequest request;
-	{
-		QWriteLocker locker(_data->haveSentMutex());
-		auto &haveSent = _data->haveSentMap();
+	auto lock = QWriteLocker(_data->haveSentMutex());
+	auto &haveSent = _data->haveSentMap();
 
-		auto i = haveSent.find(msgId);
-		if (i == haveSent.end()) {
-			return 0;
-		}
-
-		request = i.value();
-		haveSent.erase(i);
+	auto i = haveSent.find(msgId);
+	if (i == haveSent.end()) {
+		return;
 	}
-	if (request.isSentContainer()) { // for container just resend all messages we can
+	auto request = i.value();
+	haveSent.erase(i);
+	lock.unlock();
+
+	// For container just resend all messages we can.
+	if (request.isSentContainer()) {
 		DEBUG_LOG(("Message Info: resending container from haveSent, msgId %1").arg(msgId));
 		const mtpMsgId *ids = (const mtpMsgId *)(request->constData() + 8);
 		for (uint32 i = 0, l = (request->size() - 8) >> 1; i < l; ++i) {
 			resend(ids[i], 10, true);
 		}
-		return 0xFFFFFFFF;
 	} else if (!request.isStateRequest()) {
 		request->msDate = forceContainer ? 0 : crl::now();
-		sendPrepared(request, msCanWait, false);
 		{
 			QWriteLocker locker(_data->toResendMutex());
 			_data->toResendMap().insert(msgId, request->requestId);
 		}
-		return request->requestId;
-	} else {
-		return 0;
+		sendPrepared(request, msCanWait, false);
 	}
 }
 
@@ -636,8 +642,11 @@ void Session::resendAll() {
 		}
 	}
 	for (uint32 i = 0, l = toResend.size(); i < l; ++i) {
-		resend(toResend[i], 10, true);
+		resend(toResend[i], -1, true);
 	}
+	InvokeQueued(this, [=] {
+		sendAnything();
+	});
 }
 
 void Session::sendPrepared(
@@ -657,8 +666,11 @@ void Session::sendPrepared(
 	}
 
 	DEBUG_LOG(("MTP Info: added, requestId %1").arg(request->requestId));
-
-	sendAnything(msCanWait);
+	if (msCanWait >= 0) {
+		InvokeQueued(this, [=] {
+			sendAnything(msCanWait);
+		});
+	}
 }
 
 bool Session::acquireKeyCreation() {
diff --git a/Telegram/SourceFiles/mtproto/session.h b/Telegram/SourceFiles/mtproto/session.h
index 7432bec33..b3034dcc8 100644
--- a/Telegram/SourceFiles/mtproto/session.h
+++ b/Telegram/SourceFiles/mtproto/session.h
@@ -140,16 +140,8 @@ public:
 	SessionData(not_null<Session*> creator) : _owner(creator) {
 	}
 
-	void setCurrentKeyId(uint64 keyId);
-	void setSessionId(uint64 sessionId) {
-		DEBUG_LOG(("MTP Info: setting server_session: %1").arg(sessionId));
-
-		QWriteLocker locker(&_lock);
-		if (_sessionId != sessionId) {
-			_sessionId = sessionId;
-			_messagesSent = 0;
-		}
-	}
+	bool setCurrentKeyId(uint64 keyId);
+	void changeSessionId();
 	[[nodiscard]] uint64 getSessionId() const {
 		QReadLocker locker(&_lock);
 		return _sessionId;
@@ -254,12 +246,8 @@ public:
 		return _owner;
 	}
 
-	uint32 nextRequestSeqNumber(bool needAck = true) {
-		QWriteLocker locker(&_lock);
-		auto result = _messagesSent;
-		_messagesSent += (needAck ? 1 : 0);
-		return result * 2 + (needAck ? 1 : 0);
-	}
+	[[nodiscard]] bool markSessionAsStarted();
+	[[nodiscard]] uint32 nextRequestSeqNumber(bool needAck);
 
 	void clearForNewKey(not_null<Instance*> instance);
 
@@ -267,18 +255,9 @@ public:
 	void queueTryToReceive();
 	void queueNeedToResumeAndSend();
 	void queueConnectionStateChange(int newState);
-	void queueResendAll();
 	void queueResetDone();
 	void queueSendAnything(crl::time msCanWait = 0);
 	void queueSendMsgsStateInfo(quint64 msgId, QByteArray data);
-	void queueResend(
-		mtpMsgId msgId,
-		crl::time msCanWait,
-		bool forceContainer);
-	void queueResendMany(
-		QVector<mtpMsgId> msgIds,
-		crl::time msCanWait,
-		bool forceContainer);
 
 	[[nodiscard]] bool connectionInited() const;
 	[[nodiscard]] AuthKeyPtr getPersistentKey() const;
@@ -289,10 +268,17 @@ public:
 		const AuthKeyPtr &persistentKey);
 	void releaseKeyCreationOnFail();
 	void destroyTemporaryKey(uint64 keyId);
+	void resend(
+		mtpMsgId msgId,
+		crl::time msCanWait,
+		bool forceContainer);
+	void resendAll();
 
 	void detach();
 
 private:
+	void changeSessionIdLocked();
+
 	template <typename Callback>
 	void withSession(Callback &&callback);
 
@@ -300,6 +286,7 @@ private:
 	uint64 _sessionId = 0;
 	uint64 _salt = 0;
 	uint32 _messagesSent = 0;
+	bool _sessionMarkedAsStarted = false;
 
 	Session *_owner = nullptr;
 	mutable QMutex _ownerMutex;
@@ -355,6 +342,18 @@ public:
 	[[nodiscard]] AuthKeyPtr getPersistentKey() const;
 	[[nodiscard]] AuthKeyPtr getTemporaryKey() const;
 	[[nodiscard]] bool connectionInited() const;
+	void resend(
+		mtpMsgId msgId,
+		crl::time msCanWait = 0,
+		bool forceContainer = false);
+	void resendAll();
+
+	// Thread-safe.
+	// Nulls msgId and seqNo in request, if newRequest = true.
+	void sendPrepared(
+		const SecureRequest &request,
+		crl::time msCanWait = 0,
+		bool newRequest = true);
 
 	// Connection thread.
 	[[nodiscard]] bool acquireKeyCreation();
@@ -374,23 +373,12 @@ public:
 
 	void sendDcKeyCheck(const AuthKeyPtr &key);
 
-	// Nulls msgId and seqNo in request, if newRequest = true.
-	void sendPrepared(
-		const SecureRequest &request,
-		crl::time msCanWait = 0,
-		bool newRequest = true);
-
 	void tryToReceive();
 	void needToResumeAndSend();
 	void connectionStateChange(int newState);
-	void resendAll(); // After connection restart.
 	void resetDone();
 	void sendAnything(crl::time msCanWait = 0);
 	void sendMsgsStateInfo(quint64 msgId, QByteArray data);
-	mtpRequestId resend(
-		mtpMsgId msgId,
-		crl::time msCanWait = 0,
-		bool forceContainer = false);
 
 signals:
 	void authKeyChanged();