Revert "Add experimental support for sharding event persister. (#8170)" (#8242)

* Revert "Add experimental support for sharding event persister. (#8170)"

This reverts commit 82c1ee1c22a87b9e6e3179947014b0f11c0a1ac3.

* Changelog

7 files changed, 26 insertions, 100 deletions

diff --git a/synapse/storage/databases/__init__.py b/synapse/storage/databases/__init__.py
index c73d54fb67..0ac854aee2 100644
--- a/synapse/storage/databases/__init__.py
+++ b/synapse/storage/databases/__init__.py
@@ -68,7 +68,7 @@ class Databases(object):
 
                     # If we're on a process that can persist events also
                     # instantiate a `PersistEventsStore`
-                    if hs.get_instance_name() in hs.config.worker.writers.events:
+                    if hs.config.worker.writers.events == hs.get_instance_name():
                         persist_events = PersistEventsStore(hs, database, main)
 
                 if "state" in database_config.databases:
diff --git a/synapse/storage/databases/main/event_federation.py b/synapse/storage/databases/main/event_federation.py
index 4c3c162acf..0b69aa6a94 100644
--- a/synapse/storage/databases/main/event_federation.py
+++ b/synapse/storage/databases/main/event_federation.py
@@ -438,7 +438,7 @@ class EventFederationWorkerStore(EventsWorkerStore, SignatureWorkerStore, SQLBas
         """
 
         if stream_ordering <= self.stream_ordering_month_ago:
-            raise StoreError(400, "stream_ordering too old %s" % (stream_ordering,))
+            raise StoreError(400, "stream_ordering too old")
 
         sql = """
                 SELECT event_id FROM stream_ordering_to_exterm
diff --git a/synapse/storage/databases/main/events.py b/synapse/storage/databases/main/events.py
index b94fe7ac17..b3d27a2ee7 100644
--- a/synapse/storage/databases/main/events.py
+++ b/synapse/storage/databases/main/events.py
@@ -97,7 +97,6 @@ class PersistEventsStore:
         self.store = main_data_store
         self.database_engine = db.engine
         self._clock = hs.get_clock()
-        self._instance_name = hs.get_instance_name()
 
         self._ephemeral_messages_enabled = hs.config.enable_ephemeral_messages
         self.is_mine_id = hs.is_mine_id
@@ -109,7 +108,7 @@ class PersistEventsStore:
 
         # This should only exist on instances that are configured to write
         assert (
-            hs.get_instance_name() in hs.config.worker.writers.events
+            hs.config.worker.writers.events == hs.get_instance_name()
         ), "Can only instantiate EventsStore on master"
 
     async def _persist_events_and_state_updates(
@@ -801,7 +800,6 @@ class PersistEventsStore:
             table="events",
             values=[
                 {
-                    "instance_name": self._instance_name,
                     "stream_ordering": event.internal_metadata.stream_ordering,
                     "topological_ordering": event.depth,
                     "depth": event.depth,
diff --git a/synapse/storage/databases/main/events_worker.py b/synapse/storage/databases/main/events_worker.py
index 17f5997b89..a7a73cc3d8 100644
--- a/synapse/storage/databases/main/events_worker.py
+++ b/synapse/storage/databases/main/events_worker.py
@@ -42,8 +42,7 @@ from synapse.replication.tcp.streams import BackfillStream
 from synapse.replication.tcp.streams.events import EventsStream
 from synapse.storage._base import SQLBaseStore, db_to_json, make_in_list_sql_clause
 from synapse.storage.database import DatabasePool
-from synapse.storage.engines import PostgresEngine
-from synapse.storage.util.id_generators import MultiWriterIdGenerator, StreamIdGenerator
+from synapse.storage.util.id_generators import StreamIdGenerator
 from synapse.types import Collection, get_domain_from_id
 from synapse.util.caches.descriptors import Cache, cached
 from synapse.util.iterutils import batch_iter
@@ -79,54 +78,27 @@ class EventsWorkerStore(SQLBaseStore):
     def __init__(self, database: DatabasePool, db_conn, hs):
         super(EventsWorkerStore, self).__init__(database, db_conn, hs)
 
-        if isinstance(database.engine, PostgresEngine):
-            # If we're using Postgres than we can use `MultiWriterIdGenerator`
-            # regardless of whether this process writes to the streams or not.
-            self._stream_id_gen = MultiWriterIdGenerator(
-                db_conn=db_conn,
-                db=database,
-                instance_name=hs.get_instance_name(),
-                table="events",
-                instance_column="instance_name",
-                id_column="stream_ordering",
-                sequence_name="events_stream_seq",
+        if hs.config.worker.writers.events == hs.get_instance_name():
+            # We are the process in charge of generating stream ids for events,
+            # so instantiate ID generators based on the database
+            self._stream_id_gen = StreamIdGenerator(
+                db_conn, "events", "stream_ordering",
             )
-            self._backfill_id_gen = MultiWriterIdGenerator(
-                db_conn=db_conn,
-                db=database,
-                instance_name=hs.get_instance_name(),
-                table="events",
-                instance_column="instance_name",
-                id_column="stream_ordering",
-                sequence_name="events_backfill_stream_seq",
-                positive=False,
+            self._backfill_id_gen = StreamIdGenerator(
+                db_conn,
+                "events",
+                "stream_ordering",
+                step=-1,
+                extra_tables=[("ex_outlier_stream", "event_stream_ordering")],
             )
         else:
-            # We shouldn't be running in worker mode with SQLite, but its useful
-            # to support it for unit tests.
-            #
-            # If this process is the writer than we need to use
-            # `StreamIdGenerator`, otherwise we use `SlavedIdTracker` which gets
-            # updated over replication. (Multiple writers are not supported for
-            # SQLite).
-            if hs.get_instance_name() in hs.config.worker.writers.events:
-                self._stream_id_gen = StreamIdGenerator(
-                    db_conn, "events", "stream_ordering",
-                )
-                self._backfill_id_gen = StreamIdGenerator(
-                    db_conn,
-                    "events",
-                    "stream_ordering",
-                    step=-1,
-                    extra_tables=[("ex_outlier_stream", "event_stream_ordering")],
-                )
-            else:
-                self._stream_id_gen = SlavedIdTracker(
-                    db_conn, "events", "stream_ordering"
-                )
-                self._backfill_id_gen = SlavedIdTracker(
-                    db_conn, "events", "stream_ordering", step=-1
-                )
+            # Another process is in charge of persisting events and generating
+            # stream IDs: rely on the replication streams to let us know which
+            # IDs we can process.
+            self._stream_id_gen = SlavedIdTracker(db_conn, "events", "stream_ordering")
+            self._backfill_id_gen = SlavedIdTracker(
+                db_conn, "events", "stream_ordering", step=-1
+            )
 
         self._get_event_cache = Cache(
             "*getEvent*",
diff --git a/synapse/storage/databases/main/schema/delta/58/14events_instance_name.sql b/synapse/storage/databases/main/schema/delta/58/14events_instance_name.sql
deleted file mode 100644
index 98ff76d709..0000000000
--- a/synapse/storage/databases/main/schema/delta/58/14events_instance_name.sql
+++ /dev/null
@@ -1,16 +0,0 @@
-/* Copyright 2020 The Matrix.org Foundation C.I.C.
- *
- * 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.
- */
-
-ALTER TABLE events ADD COLUMN instance_name TEXT;
diff --git a/synapse/storage/databases/main/schema/delta/58/14events_instance_name.sql.postgres b/synapse/storage/databases/main/schema/delta/58/14events_instance_name.sql.postgres
deleted file mode 100644
index 97c1e6a0c5..0000000000
--- a/synapse/storage/databases/main/schema/delta/58/14events_instance_name.sql.postgres
+++ /dev/null
@@ -1,26 +0,0 @@
-/* Copyright 2020 The Matrix.org Foundation C.I.C.
- *
- * 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.
- */
-
-CREATE SEQUENCE IF NOT EXISTS events_stream_seq;
-
-SELECT setval('events_stream_seq', (
-    SELECT COALESCE(MAX(stream_ordering), 1) FROM events
-));
-
-CREATE SEQUENCE IF NOT EXISTS events_backfill_stream_seq;
-
-SELECT setval('events_backfill_stream_seq', (
-    SELECT COALESCE(-MIN(stream_ordering), 1) FROM events
-));
diff --git a/synapse/storage/util/id_generators.py b/synapse/storage/util/id_generators.py
index 8fd21c2bf8..9f3d23f0a5 100644
--- a/synapse/storage/util/id_generators.py
+++ b/synapse/storage/util/id_generators.py
@@ -231,12 +231,8 @@ class MultiWriterIdGenerator:
         # gaps should be relatively rare it's still worth doing the book keeping
         # that allows us to skip forwards when there are gapless runs of
         # positions.
-        #
-        # We start at 1 here as a) the first generated stream ID will be 2, and
-        # b) other parts of the code assume that stream IDs are strictly greater
-        # than 0.
         self._persisted_upto_position = (
-            min(self._current_positions.values()) if self._current_positions else 1
+            min(self._current_positions.values()) if self._current_positions else 0
         )
         self._known_persisted_positions = []  # type: List[int]
 
@@ -366,7 +362,9 @@ class MultiWriterIdGenerator:
         equal to it have been successfully persisted.
         """
 
-        return self.get_persisted_upto_position()
+        # Currently we don't support this operation, as it's not obvious how to
+        # condense the stream positions of multiple writers into a single int.
+        raise NotImplementedError()
 
     def get_current_token_for_writer(self, instance_name: str) -> int:
         """Returns the position of the given writer.