Create profile_updates_per_user

This table tracks which users should receive profile updates. It is intended as a write-heavy, cheap-read mechanism.

At profile update time, the homeserver determines all the users that should receive the update. At the point of /sync, we then quickly read this table and check for any relevant updates for the syncing user.

The timestamp field will be used to cull the table over time (so it doesn't grow indefinitely).

synapse/storage/schema/main/delta/95/01_profile_updates.sql

@@ -33,3 +33,17 @@ CREATE TABLE profile_updates (
 
 CREATE INDEX profile_updates_by_user ON profile_updates (user_id, stream_id);
 CREATE INDEX profile_updates_by_field ON profile_updates (field_name, stream_id);
+
+-- Track which local users should receive each profile update.
+CREATE TABLE profile_updates_per_user (
+  stream_id BIGINT NOT NULL,
+
+  -- The full user ID of the local user that should receive the profile update.
+  user_id TEXT NOT NULL,
+
+  -- Unix timestamp. Used to determine when to cull rows (to prevent the table
+  -- from growing indefinitely).
+  inserted_ts BIGINT NOT NULL
+);
+
+CREATE INDEX profile_updates_per_user_by_user_stream ON profile_updates_per_user (user_id, stream_id);