Stream ordering and out of order insertions.

Handle the fact that events can be persisted out of order, and so to get
the "current max" stream token becomes non trivial - as we need to make
sure that *all* stream tokens less than the current max have also
successfully been persisted.

synapse/storage/_base.py

@@ -22,6 +22,8 @@ from synapse.util.logcontext import PreserveLoggingContext, LoggingContext
 from synapse.util.lrucache import LruCache
 import synapse.metrics
 
+from util.id_generators import IdGenerator, StreamIdGenerator
+
 from twisted.internet import defer
 
 from collections import namedtuple, OrderedDict
@@ -29,7 +31,6 @@ import functools
 import simplejson as json
 import sys
 import time
-import threading
 
 
 logger = logging.getLogger(__name__)
@@ -232,46 +233,6 @@ class PerformanceCounters(object):
         return top_n_counters
 
 
-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 SQLBaseStore(object):
     _TXN_ID = 0
 
@@ -297,7 +258,7 @@ class SQLBaseStore(object):
         # Pretend the getEventCache is just another named cache
         caches_by_name["*getEvent*"] = self._get_event_cache
 
-        self._stream_id_gen = IdGenerator("events", "stream_ordering", self)
+        self._stream_id_gen = StreamIdGenerator()
         self._transaction_id_gen = IdGenerator("sent_transactions", "id", self)
         self._state_groups_id_gen = IdGenerator("state_groups", "id", self)
         self._access_tokens_id_gen = IdGenerator("access_tokens", "id", self)
@@ -363,7 +324,6 @@ class SQLBaseStore(object):
                                 *args, **kwargs
                             )
                         except self.database_engine.module.DatabaseError as e:
-                            logger.warn("[TXN DEADLOCK] {%s} %r, %r", name, e.errno, e.sqlstate)
                             if self.database_engine.is_deadlock(e):
                                 logger.warn("[TXN DEADLOCK] {%s} %d/%d", name, i, N)
                                 if i < N:

synapse/storage/events.py

@@ -52,7 +52,6 @@ class EventsStore(SQLBaseStore):
                 is_new_state=is_new_state,
                 current_state=current_state,
             )
-            self.get_room_events_max_id.invalidate()
         except _RollbackButIsFineException:
             pass
 
@@ -97,7 +96,13 @@ class EventsStore(SQLBaseStore):
         self._get_event_cache.pop(event.event_id)
 
         if stream_ordering is None:
-            stream_ordering = self._stream_id_gen.get_next_txn(txn)
+            with self._stream_id_gen.get_next_txn(txn) as stream_ordering:
+                return self._persist_event_txn(
+                    txn, event, context, backfilled,
+                    stream_ordering=stream_ordering,
+                    is_new_state=is_new_state,
+                    current_state=current_state,
+                )
 
         # We purposefully do this first since if we include a `current_state`
         # key, we *want* to update the `current_state_events` table

synapse/storage/stream.py

@@ -413,12 +413,10 @@ class StreamStore(SQLBaseStore):
             "get_recent_events_for_room", get_recent_events_for_room_txn
         )
 
-    @cached(num_args=0)
+    @defer.inlineCallbacks
     def get_room_events_max_id(self):
-        return self.runInteraction(
+        token = yield self._stream_id_gen.get_max_token(self)
-            "get_room_events_max_id",
+        defer.returnValue("s%d" % (token,))
-            self._get_room_events_max_id_txn
-        )
 
     @defer.inlineCallbacks
     def _get_min_token(self):
@@ -433,21 +431,6 @@ class StreamStore(SQLBaseStore):
 
         defer.returnValue(self.min_token)
 
-    def _get_room_events_max_id_txn(self, txn):
-        txn.execute(
-            "SELECT MAX(stream_ordering) as m FROM events"
-        )
-
-        res = self.cursor_to_dict(txn)
-
-        logger.debug("get_room_events_max_id: %s", res)
-
-        if not res or not res[0] or not res[0]["m"]:
-            return "s0"
-
-        key = res[0]["m"]
-        return "s%d" % (key,)
-
     @staticmethod
     def _set_before_and_after(events, rows):
         for event, row in zip(events, rows):

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.

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