Merge pull request #489 from matrix-org/markjh/replication

Add a /replication API for extracting the updates that happened on synapse.

11 files changed, 583 insertions, 2 deletions

diff --git a/synapse/app/homeserver.py b/synapse/app/homeserver.py
index 2b4be7bdd0..de5ee988f1 100755
--- a/synapse/app/homeserver.py
+++ b/synapse/app/homeserver.py
@@ -63,6 +63,7 @@ from synapse.config.homeserver import HomeServerConfig
 from synapse.crypto import context_factory
 from synapse.util.logcontext import LoggingContext
 from synapse.metrics.resource import MetricsResource, METRICS_PREFIX
+from synapse.replication.resource import ReplicationResource, REPLICATION_PREFIX
 from synapse.federation.transport.server import TransportLayerServer
 
 from synapse import events
@@ -169,6 +170,9 @@ class SynapseHomeServer(HomeServer):
                 if name == "metrics" and self.get_config().enable_metrics:
                     resources[METRICS_PREFIX] = MetricsResource(self)
 
+                if name == "replication":
+                    resources[REPLICATION_PREFIX] = ReplicationResource(self)
+
         root_resource = create_resource_tree(resources)
         if tls:
             reactor.listenSSL(
diff --git a/synapse/handlers/presence.py b/synapse/handlers/presence.py
index 08e38cdd25..d98e80086e 100644
--- a/synapse/handlers/presence.py
+++ b/synapse/handlers/presence.py
@@ -774,6 +774,25 @@ class PresenceHandler(BaseHandler):
 
         defer.returnValue(observer_user.to_string() in accepted_observers)
 
+    @defer.inlineCallbacks
+    def get_all_presence_updates(self, last_id, current_id):
+        """
+        Gets a list of presence update rows from between the given stream ids.
+        Each row has:
+        - stream_id(str)
+        - user_id(str)
+        - state(str)
+        - last_active_ts(int)
+        - last_federation_update_ts(int)
+        - last_user_sync_ts(int)
+        - status_msg(int)
+        - currently_active(int)
+        """
+        # TODO(markjh): replicate the unpersisted changes.
+        # This could use the in-memory stores for recent changes.
+        rows = yield self.store.get_all_presence_updates(last_id, current_id)
+        defer.returnValue(rows)
+
 
 def should_notify(old_state, new_state):
     """Decides if a presence state change should be sent to interested parties.
diff --git a/synapse/handlers/typing.py b/synapse/handlers/typing.py
index b16d0017df..8ce27f49ec 100644
--- a/synapse/handlers/typing.py
+++ b/synapse/handlers/typing.py
@@ -25,6 +25,7 @@ from synapse.types import UserID
 import logging
 
 from collections import namedtuple
+import ujson as json
 
 logger = logging.getLogger(__name__)
 
@@ -219,6 +220,19 @@ class TypingNotificationHandler(BaseHandler):
                 "typing_key", self._latest_room_serial, rooms=[room_id]
             )
 
+    def get_all_typing_updates(self, last_id, current_id):
+        # TODO: Work out a way to do this without scanning the entire state.
+        rows = []
+        for room_id, serial in self._room_serials.items():
+            if last_id < serial and serial <= current_id:
+                typing = self._room_typing[room_id]
+                typing_bytes = json.dumps([
+                    u.to_string() for u in typing
+                ], ensure_ascii=False)
+                rows.append((serial, room_id, typing_bytes))
+        rows.sort()
+        return rows
+
 
 class TypingNotificationEventSource(object):
     def __init__(self, hs):
diff --git a/synapse/notifier.py b/synapse/notifier.py
index 560866b26e..3c36a20868 100644
--- a/synapse/notifier.py
+++ b/synapse/notifier.py
@@ -159,6 +159,8 @@ class Notifier(object):
             self.remove_expired_streams, self.UNUSED_STREAM_EXPIRY_MS
         )
 
+        self.replication_deferred = ObservableDeferred(defer.Deferred())
+
         # This is not a very cheap test to perform, but it's only executed
         # when rendering the metrics page, which is likely once per minute at
         # most when scraping it.
@@ -207,6 +209,8 @@ class Notifier(object):
             ))
             self._notify_pending_new_room_events(max_room_stream_id)
 
+            self.notify_replication()
+
     def _notify_pending_new_room_events(self, max_room_stream_id):
         """Notify for the room events that were queued waiting for a previous
         event to be persisted.
@@ -276,6 +280,8 @@ class Notifier(object):
                 except:
                     logger.exception("Failed to notify listener")
 
+            self.notify_replication()
+
     @defer.inlineCallbacks
     def wait_for_events(self, user_id, timeout, callback, room_ids=None,
                         from_token=StreamToken("s0", "0", "0", "0", "0")):
@@ -479,3 +485,45 @@ class Notifier(object):
             room_streams = self.room_to_user_streams.setdefault(room_id, set())
             room_streams.add(new_user_stream)
             new_user_stream.rooms.add(room_id)
+
+    def notify_replication(self):
+        """Notify the any replication listeners that there's a new event"""
+        with PreserveLoggingContext():
+            deferred = self.replication_deferred
+            self.replication_deferred = ObservableDeferred(defer.Deferred())
+            deferred.callback(None)
+
+    @defer.inlineCallbacks
+    def wait_for_replication(self, callback, timeout):
+        """Wait for an event to happen.
+
+        :param callback:
+            Gets called whenever an event happens. If this returns a truthy
+            value then ``wait_for_replication`` returns, otherwise it waits
+            for another event.
+        :param int timeout:
+            How many milliseconds to wait for callback return a truthy value.
+        :returns:
+            A deferred that resolves with the value returned by the callback.
+        """
+        listener = _NotificationListener(None)
+
+        def timed_out():
+            listener.deferred.cancel()
+
+        timer = self.clock.call_later(timeout / 1000., timed_out)
+        while True:
+            listener.deferred = self.replication_deferred.observe()
+            result = yield callback()
+            if result:
+                break
+
+            try:
+                with PreserveLoggingContext():
+                    yield listener.deferred
+            except defer.CancelledError:
+                break
+
+        self.clock.cancel_call_later(timer, ignore_errs=True)
+
+        defer.returnValue(result)
diff --git a/synapse/replication/__init__.py b/synapse/replication/__init__.py
new file mode 100644
index 0000000000..b7df13c9ee
--- /dev/null
+++ b/synapse/replication/__init__.py
@@ -0,0 +1,14 @@
+# -*- coding: utf-8 -*-
+# Copyright 2016 OpenMarket Ltd
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
diff --git a/synapse/replication/resource.py b/synapse/replication/resource.py
new file mode 100644
index 0000000000..e0d039518d
--- /dev/null
+++ b/synapse/replication/resource.py
@@ -0,0 +1,320 @@
+# -*- coding: utf-8 -*-
+# Copyright 2015 OpenMarket Ltd
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+from synapse.http.servlet import parse_integer, parse_string
+from synapse.http.server import request_handler, finish_request
+
+from twisted.web.resource import Resource
+from twisted.web.server import NOT_DONE_YET
+from twisted.internet import defer
+
+import ujson as json
+
+import collections
+import logging
+
+logger = logging.getLogger(__name__)
+
+REPLICATION_PREFIX = "/_synapse/replication"
+
+STREAM_NAMES = (
+    ("events",),
+    ("presence",),
+    ("typing",),
+    ("receipts",),
+    ("user_account_data", "room_account_data", "tag_account_data",),
+    ("backfill",),
+)
+
+
+class ReplicationResource(Resource):
+    """
+    HTTP endpoint for extracting data from synapse.
+
+    The streams of data returned by the endpoint are controlled by the
+    parameters given to the API. To return a given stream pass a query
+    parameter with a position in the stream to return data from or the
+    special value "-1" to return data from the start of the stream.
+
+    If there is no data for any of the supplied streams after the given
+    position then the request will block until there is data for one
+    of the streams. This allows clients to long-poll this API.
+
+    The possible streams are:
+
+    * "streams": A special stream returing the positions of other streams.
+    * "events": The new events seen on the server.
+    * "presence": Presence updates.
+    * "typing": Typing updates.
+    * "receipts": Receipt updates.
+    * "user_account_data": Top-level per user account data.
+    * "room_account_data: Per room per user account data.
+    * "tag_account_data": Per room per user tags.
+    * "backfill": Old events that have been backfilled from other servers.
+
+    The API takes two additional query parameters:
+
+    * "timeout": How long to wait before returning an empty response.
+    * "limit": The maximum number of rows to return for the selected streams.
+
+    The response is a JSON object with keys for each stream with updates. Under
+    each key is a JSON object with:
+
+    * "postion": The current position of the stream.
+    * "field_names": The names of the fields in each row.
+    * "rows": The updates as an array of arrays.
+
+    There are a number of ways this API could be used:
+
+    1) To replicate the contents of the backing database to another database.
+    2) To be notified when the contents of a shared backing database changes.
+    3) To "tail" the activity happening on a server for debugging.
+
+    In the first case the client would track all of the streams and store it's
+    own copy of the data.
+
+    In the second case the client might theoretically just be able to follow
+    the "streams" stream to track where the other streams are. However in
+    practise it will probably need to get the contents of the streams in
+    order to expire the any in-memory caches. Whether it gets the contents
+    of the streams from this replication API or directly from the backing
+    store is a matter of taste.
+
+    In the third case the client would use the "streams" stream to find what
+    streams are available and their current positions. Then it can start
+    long-polling this replication API for new data on those streams.
+    """
+
+    isLeaf = True
+
+    def __init__(self, hs):
+        Resource.__init__(self)  # Resource is old-style, so no super()
+
+        self.version_string = hs.version_string
+        self.store = hs.get_datastore()
+        self.sources = hs.get_event_sources()
+        self.presence_handler = hs.get_handlers().presence_handler
+        self.typing_handler = hs.get_handlers().typing_notification_handler
+        self.notifier = hs.notifier
+
+    def render_GET(self, request):
+        self._async_render_GET(request)
+        return NOT_DONE_YET
+
+    @defer.inlineCallbacks
+    def current_replication_token(self):
+        stream_token = yield self.sources.get_current_token()
+        backfill_token = yield self.store.get_current_backfill_token()
+
+        defer.returnValue(_ReplicationToken(
+            stream_token.room_stream_id,
+            int(stream_token.presence_key),
+            int(stream_token.typing_key),
+            int(stream_token.receipt_key),
+            int(stream_token.account_data_key),
+            backfill_token,
+        ))
+
+    @request_handler
+    @defer.inlineCallbacks
+    def _async_render_GET(self, request):
+        limit = parse_integer(request, "limit", 100)
+        timeout = parse_integer(request, "timeout", 10 * 1000)
+
+        request.setHeader(b"Content-Type", b"application/json")
+        writer = _Writer(request)
+
+        @defer.inlineCallbacks
+        def replicate():
+            current_token = yield self.current_replication_token()
+            logger.info("Replicating up to %r", current_token)
+
+            yield self.account_data(writer, current_token, limit)
+            yield self.events(writer, current_token, limit)
+            yield self.presence(writer, current_token)  # TODO: implement limit
+            yield self.typing(writer, current_token)  # TODO: implement limit
+            yield self.receipts(writer, current_token, limit)
+            self.streams(writer, current_token)
+
+            logger.info("Replicated %d rows", writer.total)
+            defer.returnValue(writer.total)
+
+        yield self.notifier.wait_for_replication(replicate, timeout)
+
+        writer.finish()
+
+    def streams(self, writer, current_token):
+        request_token = parse_string(writer.request, "streams")
+
+        streams = []
+
+        if request_token is not None:
+            if request_token == "-1":
+                for names, position in zip(STREAM_NAMES, current_token):
+                    streams.extend((name, position) for name in names)
+            else:
+                items = zip(
+                    STREAM_NAMES,
+                    current_token,
+                    _ReplicationToken(request_token)
+                )
+                for names, current_id, last_id in items:
+                    if last_id < current_id:
+                        streams.extend((name, current_id) for name in names)
+
+            if streams:
+                writer.write_header_and_rows(
+                    "streams", streams, ("name", "position"),
+                    position=str(current_token)
+                )
+
+    @defer.inlineCallbacks
+    def events(self, writer, current_token, limit):
+        request_events = parse_integer(writer.request, "events")
+        request_backfill = parse_integer(writer.request, "backfill")
+
+        if request_events is not None or request_backfill is not None:
+            if request_events is None:
+                request_events = current_token.events
+            if request_backfill is None:
+                request_backfill = current_token.backfill
+            events_rows, backfill_rows = yield self.store.get_all_new_events(
+                request_backfill, request_events,
+                current_token.backfill, current_token.events,
+                limit
+            )
+            writer.write_header_and_rows(
+                "events", events_rows, ("position", "internal", "json")
+            )
+            writer.write_header_and_rows(
+                "backfill", backfill_rows, ("position", "internal", "json")
+            )
+
+    @defer.inlineCallbacks
+    def presence(self, writer, current_token):
+        current_position = current_token.presence
+
+        request_presence = parse_integer(writer.request, "presence")
+
+        if request_presence is not None:
+            presence_rows = yield self.presence_handler.get_all_presence_updates(
+                request_presence, current_position
+            )
+            writer.write_header_and_rows("presence", presence_rows, (
+                "position", "user_id", "state", "last_active_ts",
+                "last_federation_update_ts", "last_user_sync_ts",
+                "status_msg", "currently_active",
+            ))
+
+    @defer.inlineCallbacks
+    def typing(self, writer, current_token):
+        current_position = current_token.presence
+
+        request_typing = parse_integer(writer.request, "typing")
+
+        if request_typing is not None:
+            typing_rows = yield self.typing_handler.get_all_typing_updates(
+                request_typing, current_position
+            )
+            writer.write_header_and_rows("typing", typing_rows, (
+                "position", "room_id", "typing"
+            ))
+
+    @defer.inlineCallbacks
+    def receipts(self, writer, current_token, limit):
+        current_position = current_token.receipts
+
+        request_receipts = parse_integer(writer.request, "receipts")
+
+        if request_receipts is not None:
+            receipts_rows = yield self.store.get_all_updated_receipts(
+                request_receipts, current_position, limit
+            )
+            writer.write_header_and_rows("receipts", receipts_rows, (
+                "position", "room_id", "receipt_type", "user_id", "event_id", "data"
+            ))
+
+    @defer.inlineCallbacks
+    def account_data(self, writer, current_token, limit):
+        current_position = current_token.account_data
+
+        user_account_data = parse_integer(writer.request, "user_account_data")
+        room_account_data = parse_integer(writer.request, "room_account_data")
+        tag_account_data = parse_integer(writer.request, "tag_account_data")
+
+        if user_account_data is not None or room_account_data is not None:
+            if user_account_data is None:
+                user_account_data = current_position
+            if room_account_data is None:
+                room_account_data = current_position
+            user_rows, room_rows = yield self.store.get_all_updated_account_data(
+                user_account_data, room_account_data, current_position, limit
+            )
+            writer.write_header_and_rows("user_account_data", user_rows, (
+                "position", "user_id", "type", "content"
+            ))
+            writer.write_header_and_rows("room_account_data", room_rows, (
+                "position", "user_id", "room_id", "type", "content"
+            ))
+
+        if tag_account_data is not None:
+            tag_rows = yield self.store.get_all_updated_tags(
+                tag_account_data, current_position, limit
+            )
+            writer.write_header_and_rows("tag_account_data", tag_rows, (
+                "position", "user_id", "room_id", "tags"
+            ))
+
+
+class _Writer(object):
+    """Writes the streams as a JSON object as the response to the request"""
+    def __init__(self, request):
+        self.streams = {}
+        self.request = request
+        self.total = 0
+
+    def write_header_and_rows(self, name, rows, fields, position=None):
+        if not rows:
+            return
+
+        if position is None:
+            position = rows[-1][0]
+
+        self.streams[name] = {
+            "position": str(position),
+            "field_names": fields,
+            "rows": rows,
+        }
+
+        self.total += len(rows)
+
+    def finish(self):
+        self.request.write(json.dumps(self.streams, ensure_ascii=False))
+        finish_request(self.request)
+
+
+class _ReplicationToken(collections.namedtuple("_ReplicationToken", (
+    "events", "presence", "typing", "receipts", "account_data", "backfill",
+))):
+    __slots__ = []
+
+    def __new__(cls, *args):
+        if len(args) == 1:
+            return cls(*(int(value) for value in args[0].split("_")))
+        else:
+            return super(_ReplicationToken, cls).__new__(cls, *args)
+
+    def __str__(self):
+        return "_".join(str(value) for value in self)
diff --git a/synapse/storage/account_data.py b/synapse/storage/account_data.py
index 21a3240d9d..faddefe219 100644
--- a/synapse/storage/account_data.py
+++ b/synapse/storage/account_data.py
@@ -83,8 +83,40 @@ class AccountDataStore(SQLBaseStore):
             "get_account_data_for_room", get_account_data_for_room_txn
         )
 
-    def get_updated_account_data_for_user(self, user_id, stream_id, room_ids=None):
-        """Get all the client account_data for a that's changed.
+    def get_all_updated_account_data(self, last_global_id, last_room_id,
+                                     current_id, limit):
+        """Get all the client account_data that has changed on the server
+        Args:
+            last_global_id(int): The position to fetch from for top level data
+            last_room_id(int): The position to fetch from for per room data
+            current_id(int): The position to fetch up to.
+        Returns:
+            A deferred pair of lists of tuples of stream_id int, user_id string,
+            room_id string, type string, and content string.
+        """
+        def get_updated_account_data_txn(txn):
+            sql = (
+                "SELECT stream_id, user_id, account_data_type, content"
+                " FROM account_data WHERE ? < stream_id AND stream_id <= ?"
+                " ORDER BY stream_id ASC LIMIT ?"
+            )
+            txn.execute(sql, (last_global_id, current_id, limit))
+            global_results = txn.fetchall()
+
+            sql = (
+                "SELECT stream_id, user_id, room_id, account_data_type, content"
+                " FROM room_account_data WHERE ? < stream_id AND stream_id <= ?"
+                " ORDER BY stream_id ASC LIMIT ?"
+            )
+            txn.execute(sql, (last_room_id, current_id, limit))
+            room_results = txn.fetchall()
+            return (global_results, room_results)
+        return self.runInteraction(
+            "get_all_updated_account_data_txn", get_updated_account_data_txn
+        )
+
+    def get_updated_account_data_for_user(self, user_id, stream_id):
+        """Get all the client account_data for a that's changed for a user
 
         Args:
             user_id(str): The user to get the account_data for.
diff --git a/synapse/storage/events.py b/synapse/storage/events.py
index 73a152bc07..60936500d8 100644
--- a/synapse/storage/events.py
+++ b/synapse/storage/events.py
@@ -1064,3 +1064,48 @@ class EventsStore(SQLBaseStore):
             yield self._end_background_update(self.EVENT_ORIGIN_SERVER_TS_NAME)
 
         defer.returnValue(result)
+
+    def get_current_backfill_token(self):
+        """The current minimum token that backfilled events have reached"""
+
+        # TODO: Fix race with the persit_event txn by using one of the
+        # stream id managers
+        return -self.min_stream_token
+
+    def get_all_new_events(self, last_backfill_id, last_forward_id,
+                           current_backfill_id, current_forward_id, limit):
+        """Get all the new events that have arrived at the server either as
+        new events or as backfilled events"""
+        def get_all_new_events_txn(txn):
+            sql = (
+                "SELECT e.stream_ordering, ej.internal_metadata, ej.json"
+                " FROM events as e"
+                " JOIN event_json as ej"
+                " ON e.event_id = ej.event_id AND e.room_id = ej.room_id"
+                " WHERE ? < e.stream_ordering AND e.stream_ordering <= ?"
+                " ORDER BY e.stream_ordering ASC"
+                " LIMIT ?"
+            )
+            if last_forward_id != current_forward_id:
+                txn.execute(sql, (last_forward_id, current_forward_id, limit))
+                new_forward_events = txn.fetchall()
+            else:
+                new_forward_events = []
+
+            sql = (
+                "SELECT -e.stream_ordering, ej.internal_metadata, ej.json"
+                " FROM events as e"
+                " JOIN event_json as ej"
+                " ON e.event_id = ej.event_id AND e.room_id = ej.room_id"
+                " WHERE ? > e.stream_ordering AND e.stream_ordering >= ?"
+                " ORDER BY e.stream_ordering DESC"
+                " LIMIT ?"
+            )
+            if last_backfill_id != current_backfill_id:
+                txn.execute(sql, (-last_backfill_id, -current_backfill_id, limit))
+                new_backfill_events = txn.fetchall()
+            else:
+                new_backfill_events = []
+
+            return (new_forward_events, new_backfill_events)
+        return self.runInteraction("get_all_new_events", get_all_new_events_txn)
diff --git a/synapse/storage/presence.py b/synapse/storage/presence.py
index eece7f8961..4cec31e316 100644
--- a/synapse/storage/presence.py
+++ b/synapse/storage/presence.py
@@ -115,6 +115,22 @@ class PresenceStore(SQLBaseStore):
                 args
             )
 
+    def get_all_presence_updates(self, last_id, current_id):
+        def get_all_presence_updates_txn(txn):
+            sql = (
+                "SELECT stream_id, user_id, state, last_active_ts,"
+                " last_federation_update_ts, last_user_sync_ts, status_msg,"
+                " currently_active"
+                " FROM presence_stream"
+                " WHERE ? < stream_id AND stream_id <= ?"
+            )
+            txn.execute(sql, (last_id, current_id))
+            return txn.fetchall()
+
+        return self.runInteraction(
+            "get_all_presence_updates", get_all_presence_updates_txn
+        )
+
     @defer.inlineCallbacks
     def get_presence_for_users(self, user_ids):
         rows = yield self._simple_select_many_batch(
diff --git a/synapse/storage/receipts.py b/synapse/storage/receipts.py
index cd6dca4901..dbc074d6b5 100644
--- a/synapse/storage/receipts.py
+++ b/synapse/storage/receipts.py
@@ -390,3 +390,19 @@ class ReceiptsStore(SQLBaseStore):
                 "data": json.dumps(data),
             }
         )
+
+    def get_all_updated_receipts(self, last_id, current_id, limit):
+        def get_all_updated_receipts_txn(txn):
+            sql = (
+                "SELECT stream_id, room_id, receipt_type, user_id, event_id, data"
+                " FROM receipts_linearized"
+                " WHERE ? < stream_id AND stream_id <= ?"
+                " ORDER BY stream_id ASC"
+                " LIMIT ?"
+            )
+            txn.execute(sql, (last_id, current_id, limit))
+
+            return txn.fetchall()
+        return self.runInteraction(
+            "get_all_updated_receipts", get_all_updated_receipts_txn
+        )
diff --git a/synapse/storage/tags.py b/synapse/storage/tags.py
index 1127b0bd7e..a0e6b42b30 100644
--- a/synapse/storage/tags.py
+++ b/synapse/storage/tags.py
@@ -59,6 +59,59 @@ class TagsStore(SQLBaseStore):
         return deferred
 
     @defer.inlineCallbacks
+    def get_all_updated_tags(self, last_id, current_id, limit):
+        """Get all the client tags that have changed on the server
+        Args:
+            last_id(int): The position to fetch from.
+            current_id(int): The position to fetch up to.
+        Returns:
+            A deferred list of tuples of stream_id int, user_id string,
+            room_id string, tag string and content string.
+        """
+        def get_all_updated_tags_txn(txn):
+            sql = (
+                "SELECT stream_id, user_id, room_id"
+                " FROM room_tags_revisions as r"
+                " WHERE ? < stream_id AND stream_id <= ?"
+                " ORDER BY stream_id ASC LIMIT ?"
+            )
+            txn.execute(sql, (last_id, current_id, limit))
+            return txn.fetchall()
+
+        tag_ids = yield self.runInteraction(
+            "get_all_updated_tags", get_all_updated_tags_txn
+        )
+
+        def get_tag_content(txn, tag_ids):
+            sql = (
+                "SELECT tag, content"
+                " FROM room_tags"
+                " WHERE user_id=? AND room_id=?"
+            )
+            results = []
+            for stream_id, user_id, room_id in tag_ids:
+                txn.execute(sql, (user_id, room_id))
+                tags = []
+                for tag, content in txn.fetchall():
+                    tags.append(json.dumps(tag) + ":" + content)
+                tag_json = "{" + ",".join(tags) + "}"
+                results.append((stream_id, user_id, room_id, tag_json))
+
+            return results
+
+        batch_size = 50
+        results = []
+        for i in xrange(0, len(tag_ids), batch_size):
+            tags = yield self.runInteraction(
+                "get_all_updated_tag_content",
+                get_tag_content,
+                tag_ids[i:i + batch_size],
+            )
+            results.extend(tags)
+
+        defer.returnValue(results)
+
+    @defer.inlineCallbacks
     def get_updated_tags(self, user_id, stream_id):
         """Get all the tags for the rooms where the tags have changed since the
         given version