diff --git a/synapse/storage/util/__init__.py b/synapse/storage/util/__init__.py
new file mode 100644
index 0000000000..c488b10d3c
--- /dev/null
+++ b/synapse/storage/util/__init__.py
@@ -0,0 +1,14 @@
+# -*- coding: utf-8 -*-
+# Copyright 2014, 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.
diff --git a/synapse/storage/util/id_generators.py b/synapse/storage/util/id_generators.py
new file mode 100644
index 0000000000..8f419323a7
--- /dev/null
+++ b/synapse/storage/util/id_generators.py
@@ -0,0 +1,126 @@
+# -*- coding: utf-8 -*-
+# Copyright 2014, 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 twisted.internet import defer
+
+from collections import deque
+import contextlib
+import threading
+
+
+class IdGenerator(object):
+ def __init__(self, table, column, store):
+ self.table = table
+ self.column = column
+ self.store = store
+ self._lock = threading.Lock()
+ self._next_id = None
+
+ @defer.inlineCallbacks
+ def get_next(self):
+ with self._lock:
+ if not self._next_id:
+ res = yield self.store._execute_and_decode(
+ "IdGenerator_%s" % (self.table,),
+ "SELECT MAX(%s) as mx FROM %s" % (self.column, self.table,)
+ )
+
+ self._next_id = (res and res[0] and res[0]["mx"]) or 1
+
+ i = self._next_id
+ self._next_id += 1
+ defer.returnValue(i)
+
+ def get_next_txn(self, txn):
+ with self._lock:
+ if self._next_id:
+ i = self._next_id
+ self._next_id += 1
+ return i
+ else:
+ txn.execute(
+ "SELECT MAX(%s) FROM %s" % (self.column, self.table,)
+ )
+
+ val, = txn.fetchone()
+ self._next_id = val or 2
+
+ return 1
+
+
+class StreamIdGenerator(object):
+ """Used to generate new stream ids when persisting events while keeping
+ track of which transactions have been completed.
+
+ This allows us to get the "current" stream id, i.e. the stream id such that
+ all ids less than or equal to it have completed. This handles the fact that
+ persistence of events can complete out of order.
+
+ Usage:
+ with stream_id_gen.get_next_txn(txn) as stream_id:
+ # ... persist event ...
+ """
+ def __init__(self):
+ self._lock = threading.Lock()
+
+ self._current_max = None
+ self._unfinished_ids = deque()
+
+ def get_next_txn(self, txn):
+ """
+ Usage:
+ with stream_id_gen.get_next_txn(txn) as stream_id:
+ # ... persist event ...
+ """
+ with self._lock:
+ if not self._current_max:
+ self._compute_current_max(txn)
+
+ self._current_max += 1
+ next_id = self._current_max
+
+ self._unfinished_ids.append(next_id)
+
+ @contextlib.contextmanager
+ def manager():
+ yield next_id
+ with self._lock:
+ self._unfinished_ids.remove(next_id)
+
+ return manager()
+
+ def get_max_token(self, store):
+ """Returns the maximum stream id such that all stream ids less than or
+ equal to it have been successfully persisted.
+ """
+ with self._lock:
+ if self._unfinished_ids:
+ return self._unfinished_ids[0] - 1
+
+ if not self._current_max:
+ return store.runInteraction(
+ "_compute_current_max",
+ self._compute_current_max,
+ )
+
+ return self._current_max
+
+ def _compute_current_max(self, txn):
+ txn.execute("SELECT MAX(stream_ordering) FROM events")
+ val, = txn.fetchone()
+
+ self._current_max = int(val) if val else 1
+
+ return self._current_max
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