diff --git a/scripts/port_to_maria.py b/scripts/port_to_maria.py
index 6e0adf703..b14cca891 100644
--- a/scripts/port_to_maria.py
+++ b/scripts/port_to_maria.py
@@ -51,16 +51,52 @@ UNICODE_COLUMNS = {
 }
 
 
+APPEND_ONLY_TABLES = [
+    "event_content_hashes",
+    "event_reference_hashes",
+    "event_signatures",
+    "event_edge_hashes",
+    "events",
+    "event_json",
+    "state_events",
+    "room_memberships",
+    "feedback",
+    "topics",
+    "room_names",
+    "rooms",
+    "local_media_repository",
+    "local_media_repository_thumbnails",
+    "remote_media_cache",
+    "remote_media_cache_thumbnails",
+    "redactions",
+    "event_edges",
+    "event_auth",
+    "received_transactions",
+    "sent_transactions",
+    "transaction_id_to_pdu",
+    "users",
+    "state_groups",
+    "state_groups_state",
+    "event_to_state_groups",
+    "rejections",
+]
+
+
 class Store(object):
     def __init__(self, db_pool, engine):
         self.db_pool = db_pool
-        self.engine = engine
+        self.database_engine = engine
 
     _simple_insert_txn = SQLBaseStore.__dict__["_simple_insert_txn"]
     _simple_insert = SQLBaseStore.__dict__["_simple_insert"]
 
     _simple_select_onecol_txn = SQLBaseStore.__dict__["_simple_select_onecol_txn"]
     _simple_select_onecol = SQLBaseStore.__dict__["_simple_select_onecol"]
+    _simple_select_one_onecol = SQLBaseStore.__dict__["_simple_select_one_onecol"]
+    _simple_select_one_onecol_txn = SQLBaseStore.__dict__["_simple_select_one_onecol_txn"]
+
+    _simple_update_one = SQLBaseStore.__dict__["_simple_update_one"]
+    _simple_update_one_txn = SQLBaseStore.__dict__["_simple_update_one_txn"]
 
     _execute_and_decode = SQLBaseStore.__dict__["_execute_and_decode"]
 
@@ -73,11 +109,11 @@ class Store(object):
                     try:
                         txn = conn.cursor()
                         return func(
-                            LoggingTransaction(txn, desc, self.engine),
+                            LoggingTransaction(txn, desc, self.database_engine),
                             *args, **kwargs
                         )
-                    except self.engine.module.DatabaseError as e:
-                        if self.engine.is_deadlock(e):
+                    except self.database_engine.module.DatabaseError as e:
+                        if self.database_engine.is_deadlock(e):
                             logger.warn("[TXN DEADLOCK] {%s} %d/%d", desc, i, N)
                             if i < N:
                                 i += 1
@@ -117,16 +153,50 @@ def chunks(n):
 
 @defer.inlineCallbacks
 def handle_table(table, sqlite_store, mysql_store):
-    N = 1000
+    if table in APPEND_ONLY_TABLES:
+        # It's safe to just carry on inserting.
+        next_chunk = yield mysql_store._simple_select_one_onecol(
+            table="port_from_sqlite3",
+            keyvalues={"table_name": table},
+            retcol="rowid",
+            allow_none=True,
+        )
+
+        if next_chunk is None:
+            yield mysql_store._simple_insert(
+                table="port_from_sqlite3",
+                values={"table_name": table, "rowid": 0}
+            )
+
+            next_chunk = 0
+    else:
+        def delete_all(txn):
+            txn.execute(
+                "DELETE FROM port_from_sqlite3 WHERE table_name = %s",
+                (table,)
+            )
+            txn.execute("DELETE FROM %s" % (table,))
+            mysql_store._simple_insert_txn(
+                txn,
+                table="port_from_sqlite3",
+                values={"table_name": table, "rowid": 0}
+            )
+
+        yield mysql_store.runInteraction(
+            "delete_non_append_only", delete_all
+        )
+
+        next_chunk = 0
+
+    N = 5000
 
     select = "SELECT rowid, * FROM %s WHERE rowid >= ? ORDER BY rowid LIMIT ?" % (table,)
 
     uni_col_names = UNICODE_COLUMNS.get(table, [])
 
     def conv_uni(c):
-        return sqlite_store.engine.load_unicode(c)
+        return sqlite_store.database_engine.load_unicode(c)
 
-    next_chunk = 0
     while True:
         def r(txn):
             txn.execute(select, (next_chunk, N,))
@@ -145,7 +215,7 @@ def handle_table(table, sqlite_store, mysql_store):
 
             for i, row in enumerate(rows):
                 rows[i] = tuple(
-                    mysql_store.engine.encode_parameter(
+                    mysql_store.database_engine.encode_parameter(
                         conv_uni(col) if j in uni_cols else col
                     )
                     for j, col in enumerate(row)
@@ -153,6 +223,12 @@ def handle_table(table, sqlite_store, mysql_store):
                 )
 
             yield mysql_store.insert_many(table, headers[1:], rows)
+
+            yield mysql_store._simple_update_one(
+                table="port_from_sqlite3",
+                keyvalues={"table_name": table},
+                updatevalues={"rowid": next_chunk},
+            )
         else:
             return
 
@@ -208,6 +284,22 @@ def main(sqlite_config, mysql_config):
 
         logger.info("Found %d tables", len(tables))
 
+        def create_port_table(txn):
+            try:
+                txn.execute(
+                    "CREATE TABLE port_from_sqlite3 ("
+                    " `table_name` varchar(100) NOT NULL UNIQUE,"
+                    " `rowid` bigint unsigned NOT NULL"
+                    ")"
+                )
+            except mysql_engine.module.DatabaseError as e:
+                if e.errno != mysql_engine.module.errorcode.ER_TABLE_EXISTS_ERROR:
+                    raise
+
+        yield mysql_store.runInteraction(
+            "create_port_table", create_port_table
+        )
+
         # Process tables.
         yield defer.gatherResults(
             [