3 files changed, 12 insertions, 5 deletions
diff --git a/synapse/storage/engines/_base.py b/synapse/storage/engines/_base.py
index bc9ca3a53c..0363cdc038 100644
--- a/synapse/storage/engines/_base.py
+++ b/synapse/storage/engines/_base.py
@@ -133,8 +133,9 @@ class BaseDatabaseEngine(Generic[ConnectionType, CursorType], metaclass=abc.ABCM
 
         This is not provided by DBAPI2, and so needs engine-specific support.
 
-        Some database engines may automatically COMMIT the ongoing transaction both
-        before and after executing the script.
+        Any ongoing transaction is committed before executing the script in its own
+        transaction. The script transaction is left open and it is the responsibility of
+        the caller to commit it.
         """
         ...
 
diff --git a/synapse/storage/engines/postgres.py b/synapse/storage/engines/postgres.py
index f9f562ea45..b350f57ccb 100644
--- a/synapse/storage/engines/postgres.py
+++ b/synapse/storage/engines/postgres.py
@@ -220,5 +220,9 @@ class PostgresEngine(
         """Execute a chunk of SQL containing multiple semicolon-delimited statements.
 
         Psycopg2 seems happy to do this in DBAPI2's `execute()` function.
+
+        For consistency with SQLite, any ongoing transaction is committed before
+        executing the script in its own transaction. The script transaction is
+        left open and it is the responsibility of the caller to commit it.
         """
-        cursor.execute(script)
+        cursor.execute(f"COMMIT; BEGIN TRANSACTION; {script}")
diff --git a/synapse/storage/engines/sqlite.py b/synapse/storage/engines/sqlite.py
index 2f7df85ce4..28751e89a5 100644
--- a/synapse/storage/engines/sqlite.py
+++ b/synapse/storage/engines/sqlite.py
@@ -135,14 +135,16 @@ class Sqlite3Engine(BaseDatabaseEngine[sqlite3.Connection, sqlite3.Cursor]):
         > than one statement with it, it will raise a Warning. Use executescript() if
         > you want to execute multiple SQL statements with one call.
 
-        The script is wrapped in transaction control statemnets, since the docs for
+        The script is prefixed with a `BEGIN TRANSACTION`, since the docs for
         `executescript` warn:
 
         > If there is a pending transaction, an implicit COMMIT statement is executed
         > first. No other implicit transaction control is performed; any transaction
         > control must be added to sql_script.
         """
-        cursor.executescript(f"BEGIN TRANSACTION;\n{script}\nCOMMIT;")
+        # The implementation of `executescript` can be found at
+        # https://github.com/python/cpython/blob/3.11/Modules/_sqlite/cursor.c#L1035.
+        cursor.executescript(f"BEGIN TRANSACTION; {script}")
 
 
 # Following functions taken from: https://github.com/coleifer/peewee