Stop populating events.content

This field is no longer read from, so we should stop populating it. Once we're
happy that this doesn't break everything, and a rollback is unlikely, we can
think about dropping the column.

synapse/storage/events.py

@@ -1189,7 +1189,6 @@ class EventsStore(EventsWorkerStore):
                     "type": event.type,
                     "processed": True,
                     "outlier": event.internal_metadata.is_outlier(),
-                    "content": encode_json(event.content).decode("UTF-8"),
                     "origin_server_ts": int(event.origin_server_ts),
                     "received_ts": self._clock.time_msec(),
                     "sender": event.sender,

synapse/storage/schema/delta/50/make_event_content_nullable.py

@@ -0,0 +1,93 @@
+# -*- coding: utf-8 -*-
+# Copyright 2018 New Vector 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.
+
+"""
+We want to stop populating 'event.content', so we need to make it nullable.
+
+If this has to be rolled back, then the following should populate the missing data:
+
+Postgres:
+
+    UPDATE events SET content=(ej.json::json)->'content' FROM event_json ej
+    WHERE ej.event_id = events.event_id AND
+        stream_ordering < (
+            SELECT stream_ordering FROM events WHERE content IS NOT NULL
+            ORDER BY stream_ordering LIMIT 1
+        );
+
+    UPDATE events SET content=(ej.json::json)->'content' FROM event_json ej
+    WHERE ej.event_id = events.event_id AND
+        stream_ordering > (
+            SELECT stream_ordering FROM events WHERE content IS NOT NULL
+            ORDER BY stream_ordering DESC LIMIT 1
+        );
+
+SQLite:
+
+    UPDATE events SET content=(
+        SELECT json_extract(json,'$.content') FROM event_json ej
+        WHERE ej.event_id = events.event_id
+    )
+    WHERE
+        stream_ordering < (
+            SELECT stream_ordering FROM events WHERE content IS NOT NULL
+            ORDER BY stream_ordering LIMIT 1
+        )
+        OR stream_ordering > (
+            SELECT stream_ordering FROM events WHERE content IS NOT NULL
+            ORDER BY stream_ordering DESC LIMIT 1
+        );
+
+"""
+
+import logging
+
+from synapse.storage.engines import PostgresEngine
+
+logger = logging.getLogger(__name__)
+
+
+def run_create(cur, database_engine, *args, **kwargs):
+    if isinstance(database_engine, PostgresEngine):
+        cur.execute("""
+            ALTER TABLE events ALTER COLUMN content DROP NOT NULL;
+        """)
+        return
+
+    # sqlite is an arse about this. ref: https://www.sqlite.org/lang_altertable.html
+    cur.execute("PRAGMA schema_version")
+    (oldver,) = cur.fetchone()
+
+    cur.execute("SELECT sql FROM sqlite_master WHERE tbl_name='events' AND type='table'")
+    (oldsql,) = cur.fetchone()
+    sql = oldsql.replace("content TEXT NOT NULL", "content TEXT")
+    if sql == oldsql:
+        raise Exception("Couldn't find null constraint to drop in %s" % oldsql)
+
+    logger.info("Replacing definition of 'events' with: %s", sql)
+
+    cur.execute("PRAGMA writable_schema=ON")
+
+    cur.execute(
+        "UPDATE sqlite_master SET sql=? WHERE tbl_name='events' AND type='table'",
+        (sql, ),
+    )
+
+    cur.execute("PRAGMA schema_version=%i" % (oldver+1,))
+    cur.execute("PRAGMA writable_schema=OFF")
+
+
+def run_upgrade(*args, **kwargs):
+    pass