Backout unneeded changes.

synapse/storage/engines/_base.py

@@ -58,18 +58,6 @@ class BaseDatabaseEngine(Generic[ConnectionType, CursorType], metaclass=abc.ABCM
         """Do we support the `RETURNING` clause in insert/update/delete?"""
         ...
 
-    @property
-    @abc.abstractmethod
-    def supports_select_distinct_on(self) -> bool:
-        """Do we support the `DISTINCT ON` clause in SELECT?"""
-        ...
-
-    @property
-    @abc.abstractmethod
-    def supports_sequences(self) -> bool:
-        """Do we support the `CREATE SEQUENCE` clause?"""
-        ...
-
     @abc.abstractmethod
     def check_database(
         self, db_conn: ConnectionType, allow_outdated_version: bool = False

synapse/storage/engines/postgres.py

@@ -189,16 +189,6 @@ class PostgresEngine(
         """Do we support the `RETURNING` clause in insert/update/delete?"""
         return True
 
-    @property
-    def supports_select_distinct_on(self) -> bool:
-        """Do we support the `DISTINCT ON` clause in SELECT?"""
-        return True
-
-    @property
-    def supports_sequences(self) -> bool:
-        """Do we support the `CREATE SEQUENCE` clause?"""
-        return True
-
     def is_connection_closed(self, conn: ConnectionType) -> bool:
         return bool(conn.closed)
 

synapse/storage/engines/sqlite.py

@@ -65,16 +65,6 @@ class Sqlite3Engine(BaseDatabaseEngine[sqlite3.Connection, sqlite3.Cursor]):
         """Do we support the `RETURNING` clause in insert/update/delete?"""
         return sqlite3.sqlite_version_info >= (3, 35, 0)
 
-    @property
-    def supports_select_distinct_on(self) -> bool:
-        """Do we support the `DISTINCT ON` clause in SELECT?"""
-        return False
-
-    @property
-    def supports_sequences(self) -> bool:
-        """Do we support the `CREATE SEQUENCE` clause?"""
-        return False
-
     def check_database(
         self, db_conn: sqlite3.Connection, allow_outdated_version: bool = False
     ) -> None:

synapse/storage/schema/main/delta/56/unique_user_filter_index.py

@@ -2,7 +2,7 @@ import logging
 from io import StringIO
 
 from synapse.storage.database import LoggingTransaction
-from synapse.storage.engines import BaseDatabaseEngine
+from synapse.storage.engines import BaseDatabaseEngine, PostgresEngine
 from synapse.storage.prepare_database import execute_statements_from_stream
 
 logger = logging.getLogger(__name__)
@@ -18,7 +18,7 @@ This migration updates the user_filters table as follows:
 
 
 def run_create(cur: LoggingTransaction, database_engine: BaseDatabaseEngine) -> None:
-    if database_engine.supports_select_distinct_on:
+    if isinstance(database_engine, PostgresEngine):
         select_clause = """
             SELECT DISTINCT ON (user_id, filter_id) user_id, filter_id, filter_json
             FROM user_filters

synapse/storage/schema/main/delta/69/01as_txn_seq.py

@@ -18,11 +18,11 @@ Adds a postgres SEQUENCE for generating application service transaction IDs.
 """
 
 from synapse.storage.database import LoggingTransaction
-from synapse.storage.engines import BaseDatabaseEngine, PsycopgEngine
+from synapse.storage.engines import BaseDatabaseEngine, PostgresEngine, PsycopgEngine
 
 
 def run_create(cur: LoggingTransaction, database_engine: BaseDatabaseEngine) -> None:
-    if database_engine.supports_sequences:
+    if isinstance(database_engine, PostgresEngine):
         # If we already have some AS TXNs we want to start from the current
         # maximum value. There are two potential places this is stored - the
         # actual TXNs themselves *and* the AS state table. At time of migration