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Store Promise<Response> instead of Response for HTTP API transactions 

This fixes a race whereby:
 - User hits an endpoint.
 - No cached transaction so executes main code.
 - User hits same endpoint.
 - No cache transaction so executes main code.
 - Main code finishes executing and caches response and returns.
 - Main code finishes executing and caches response and returns.

 This race is common in the wild when Synapse is struggling under load.
 This commit fixes the race by:
  - User hits an endpoint.
  - Caches the promise to execute the main code and executes main code.
  - User hits same endpoint.
  - Yields on the same promise as the first request.
  - Main code finishes executing and returns, unblocking both requests.
This commit is contained in:
Kegan Dougal 2016-11-10 14:49:26 +00:00
parent 6cc4fcf25c
commit 2771447c29
4 changed files with 68 additions and 88 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

4
synapse/rest/client/v1/base.py
View File

@ -18,7 +18,7 @@
from synapse.http.servlet import RestServlet
from synapse.api.urls import CLIENT_PREFIX
from .transactions import HttpTransactionStore
from .transactions import HttpTransactionCache
import re
import logging
@ -59,4 +59,4 @@ class ClientV1RestServlet(RestServlet):
self.hs = hs
self.builder_factory = hs.get_event_builder_factory()
self.auth = hs.get_v1auth()
self.txns = HttpTransactionStore()
self.txns = HttpTransactionCache()

82
synapse/rest/client/v1/room.py
View File

@ -56,15 +56,15 @@ class RoomCreateRestServlet(ClientV1RestServlet):
@defer.inlineCallbacks
def on_PUT(self, request, txn_id):
try:
defer.returnValue(
self.txns.get_client_transaction(request, txn_id)
)
res_deferred = self.txns.get_client_transaction(request, txn_id)
res = yield res_deferred
defer.returnValue(res)
except KeyError:
pass
response = yield self.on_POST(request)
self.txns.store_client_transaction(request, txn_id, response)
res_deferred = self.on_POST(request)
self.txns.store_client_transaction(request, txn_id, res_deferred)
response = yield res_deferred
defer.returnValue(response)
@defer.inlineCallbacks
@ -217,15 +217,15 @@ class RoomSendEventRestServlet(ClientV1RestServlet):
@defer.inlineCallbacks
def on_PUT(self, request, room_id, event_type, txn_id):
try:
defer.returnValue(
self.txns.get_client_transaction(request, txn_id)
)
res_deferred = self.txns.get_client_transaction(request, txn_id)
res = yield res_deferred
defer.returnValue(res)
except KeyError:
pass
response = yield self.on_POST(request, room_id, event_type, txn_id)
self.txns.store_client_transaction(request, txn_id, response)
res_deferred = self.on_POST(request, room_id, event_type, txn_id)
self.txns.store_client_transaction(request, txn_id, res_deferred)
response = yield res_deferred
defer.returnValue(response)
@ -286,15 +286,15 @@ class JoinRoomAliasServlet(ClientV1RestServlet):
@defer.inlineCallbacks
def on_PUT(self, request, room_identifier, txn_id):
try:
defer.returnValue(
self.txns.get_client_transaction(request, txn_id)
)
res_deferred = self.txns.get_client_transaction(request, txn_id)
res = yield res_deferred
defer.returnValue(res)
except KeyError:
pass
response = yield self.on_POST(request, room_identifier, txn_id)
self.txns.store_client_transaction(request, txn_id, response)
res_deferred = self.on_POST(request, room_identifier, txn_id)
self.txns.store_client_transaction(request, txn_id, res_deferred)
response = yield res_deferred
defer.returnValue(response)
@ -540,17 +540,15 @@ class RoomForgetRestServlet(ClientV1RestServlet):
@defer.inlineCallbacks
def on_PUT(self, request, room_id, txn_id):
try:
defer.returnValue(
self.txns.get_client_transaction(request, txn_id)
)
res_deferred = self.txns.get_client_transaction(request, txn_id)
res = yield res_deferred
defer.returnValue(res)
except KeyError:
pass
response = yield self.on_POST(
request, room_id, txn_id
)
self.txns.store_client_transaction(request, txn_id, response)
res_deferred = self.on_POST(request, room_id, txn_id)
self.txns.store_client_transaction(request, txn_id, res_deferred)
response = yield res_deferred
defer.returnValue(response)
@ -626,17 +624,15 @@ class RoomMembershipRestServlet(ClientV1RestServlet):
@defer.inlineCallbacks
def on_PUT(self, request, room_id, membership_action, txn_id):
try:
defer.returnValue(
self.txns.get_client_transaction(request, txn_id)
)
res_deferred = self.txns.get_client_transaction(request, txn_id)
res = yield res_deferred
defer.returnValue(res)
except KeyError:
pass
response = yield self.on_POST(
request, room_id, membership_action, txn_id
)
self.txns.store_client_transaction(request, txn_id, response)
res_deferred = self.on_POST(request, room_id, membership_action, txn_id)
self.txns.store_client_transaction(request, txn_id, res_deferred)
response = yield res_deferred
defer.returnValue(response)
@ -672,15 +668,15 @@ class RoomRedactEventRestServlet(ClientV1RestServlet):
@defer.inlineCallbacks
def on_PUT(self, request, room_id, event_id, txn_id):
try:
defer.returnValue(
self.txns.get_client_transaction(request, txn_id)
)
res_deferred = self.txns.get_client_transaction(request, txn_id)
res = yield res_deferred
defer.returnValue(res)
except KeyError:
pass
response = yield self.on_POST(request, room_id, event_id, txn_id)
self.txns.store_client_transaction(request, txn_id, response)
res_deferred = self.on_POST(request, room_id, event_id, txn_id)
self.txns.store_client_transaction(request, txn_id, res_deferred)
response = yield res_deferred
defer.returnValue(response)

52
synapse/rest/client/v1/transactions.py
View File

@ -22,57 +22,35 @@ from synapse.api.auth import get_access_token_from_request
logger = logging.getLogger(__name__)
# FIXME: elsewhere we use FooStore to indicate something in the storage layer...
class HttpTransactionStore(object):
class HttpTransactionCache(object):
def __init__(self):
# { key : (txn_id, response) }
# { key : (txn_id, response_deferred) }
self.transactions = {}
def get_response(self, key, txn_id):
"""Retrieve a response for this request.
Args:
key (str): A transaction-independent key for this request. Usually
this is a combination of the path (without the transaction id)
and the user's access token.
txn_id (str): The transaction ID for this request
Returns:
A tuple of (HTTP response code, response content) or None.
"""
def _get_response(self, key, txn_id):
try:
logger.debug("get_response TxnId: %s", txn_id)
(last_txn_id, response) = self.transactions[key]
(last_txn_id, response_deferred) = self.transactions[key]
if txn_id == last_txn_id:
logger.info("get_response: Returning a response for %s", txn_id)
return response
return response_deferred
except KeyError:
pass
return None
def store_response(self, key, txn_id, response):
"""Stores an HTTP response tuple.
def _store_response(self, key, txn_id, response_deferred):
self.transactions[key] = (txn_id, response_deferred)
Args:
key (str): A transaction-independent key for this request. Usually
this is a combination of the path (without the transaction id)
and the user's access token.
txn_id (str): The transaction ID for this request.
response (tuple): A tuple of (HTTP response code, response content)
"""
logger.debug("store_response TxnId: %s", txn_id)
self.transactions[key] = (txn_id, response)
def store_client_transaction(self, request, txn_id, response):
"""Stores the request/response pair of an HTTP transaction.
def store_client_transaction(self, request, txn_id, response_deferred):
"""Stores the request/Promise<response> pair of an HTTP transaction.
Args:
request (twisted.web.http.Request): The twisted HTTP request. This
request must have the transaction ID as the last path segment.
response (tuple): A tuple of (response code, response dict)
response_deferred (Promise<tuple>): A tuple of (response code, response dict)
txn_id (str): The transaction ID for this request.
"""
self.store_response(self._get_key(request), txn_id, response)
self._store_response(self._get_key(request), txn_id, response_deferred)
def get_client_transaction(self, request, txn_id):
"""Retrieves a stored response if there was one.
@ -82,14 +60,14 @@ class HttpTransactionStore(object):
request must have the transaction ID as the last path segment.
txn_id (str): The transaction ID for this request.
Returns:
The response tuple.
Promise: Resolves to the response tuple.
Raises:
KeyError if the transaction was not found.
"""
response = self.get_response(self._get_key(request), txn_id)
if response is None:
response_deferred = self._get_response(self._get_key(request), txn_id)
if response_deferred is None:
raise KeyError("Transaction not found.")
return response
return response_deferred
def _get_key(self, request):
token = get_access_token_from_request(request)

18
synapse/rest/client/v2_alpha/sendtodevice.py
View File

@ -19,7 +19,7 @@ from twisted.internet import defer
from synapse.http import servlet
from synapse.http.servlet import parse_json_object_from_request
from synapse.rest.client.v1.transactions import HttpTransactionStore
from synapse.rest.client.v1.transactions import HttpTransactionCache
from ._base import client_v2_patterns
@ -40,18 +40,25 @@ class SendToDeviceRestServlet(servlet.RestServlet):
super(SendToDeviceRestServlet, self).__init__()
self.hs = hs
self.auth = hs.get_auth()
self.txns = HttpTransactionStore()
self.txns = HttpTransactionCache()
self.device_message_handler = hs.get_device_message_handler()
@defer.inlineCallbacks
def on_PUT(self, request, message_type, txn_id):
try:
defer.returnValue(
self.txns.get_client_transaction(request, txn_id)
)
res_deferred = self.txns.get_client_transaction(request, txn_id)
res = yield res_deferred
defer.returnValue(res)
except KeyError:
pass
res_deferred = self._put(request, message_type, txn_id)
self.txns.store_client_transaction(request, txn_id, res_deferred)
res = yield res_deferred
defer.returnValue(res)
@defer.inlineCallbacks
def _put(self, request, message_type, txn_id):
requester = yield self.auth.get_user_by_req(request)
content = parse_json_object_from_request(request)
@ -63,7 +70,6 @@ class SendToDeviceRestServlet(servlet.RestServlet):
)
response = (200, {})
self.txns.store_client_transaction(request, txn_id, response)
defer.returnValue(response)