Add experimental support for sharding event persister. Again. (#8294)

This is *not* ready for production yet. Caveats:

1. We should write some tests...
2. The stream token that we use for events can get stalled at the minimum position of all writers. This means that new events may not be processed and e.g. sent down sync streams if a writer isn't writing or is slow.

2 files changed, 42 insertions, 0 deletions

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
new file mode 100644
index 0000000000..98ff76d709
--- /dev/null
+++ b/synapse/storage/databases/main/schema/delta/58/14events_instance_name.sql
@@ -0,0 +1,16 @@
+/* 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
new file mode 100644
index 0000000000..97c1e6a0c5
--- /dev/null
+++ b/synapse/storage/databases/main/schema/delta/58/14events_instance_name.sql.postgres
@@ -0,0 +1,26 @@
+/* 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
+));