Change Index on user + filters to Unique

 * especially relevant since the current increment code is not atomic

synapse/storage/prepare_database.py

@@ -25,7 +25,7 @@
 
 # Remember to update this number every time a change is made to database
 # schema files, so the users will be informed on server restarts.
-SCHEMA_VERSION = 41
+SCHEMA_VERSION = 42
 
 dir_path = os.path.abspath(os.path.dirname(__file__))
 

synapse/storage/schema/delta/42/unique_user_filter_index.py

@@ -0,0 +1,39 @@
+from synapse.storage.engines import PostgresEngine
+
+import logging
+
+logger = logging.getLogger(__name__)
+
+
+def run_create(cur, database_engine, *args, **kwargs):
+    if isinstance(database_engine, PostgresEngine):
+        select_clause = '''
+        CREATE TABLE user_filters_migration AS
+            SELECT DISTINCT ON (user_id, filter_id) user_id, filter_id, filter_json
+            FROM user_filters;
+        '''
+    else:
+        select_clause = '''
+        CREATE TABLE user_filters_migration AS
+            SELECT * FROM user_filters GROUP BY user_id, filter_id;
+        '''
+    sql = '''
+        BEGIN;
+            %s
+            DROP INDEX user_filters_by_user_id_filter_id;
+            DELETE FROM user_filters;
+            INSERT INTO user_filters(user_id, filter_id, filter_json)
+                SELECT * FROM user_filters_migration;
+            DROP TABLE user_filters_migration;
+            CREATE UNIQUE INDEX user_filters_by_user_id_filter_id_unique
+                ON user_filters(user_id, filter_id);
+        END;
+    ''' % select_clause
+    if isinstance(database_engine, PostgresEngine):
+        cur.execute(sql)
+    else:
+        cur.executescript(sql)
+
+
+def run_upgrade(cur, database_engine, *args, **kwargs):
+    pass