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changelog.d/7143.bugfix

@@ -0,0 +1 @@
+Prevent `sqlite3` module from being imported even when using the postgres backend.

synapse/storage/engines/__init__.py

@@ -15,25 +15,28 @@
 import platform
 
 from ._base import BaseDatabaseEngine, IncorrectDatabaseSetup
-from .postgres import PostgresEngine
-from .sqlite import Sqlite3Engine
+
+MYPY = False
 
 
 def create_engine(database_config) -> BaseDatabaseEngine:
     name = database_config["name"]
 
-    if name == "sqlite3":
+    if name == "sqlite3" or MYPY:
         import sqlite3
+        from .sqlite import Sqlite3Engine
 
         return Sqlite3Engine(sqlite3, database_config)
 
-    if name == "psycopg2":
+    if name == "psycopg2" or MYPY:
         # pypy requires psycopg2cffi rather than psycopg2
         if platform.python_implementation() == "PyPy":
             import psycopg2cffi as psycopg2  # type: ignore
         else:
             import psycopg2  # type: ignore
 
+        from .postgres import PostgresEngine
+
         return PostgresEngine(psycopg2, database_config)
 
     raise RuntimeError("Unsupported database engine '%s'" % (name,))

synapse/storage/engines/sqlite.py

@@ -12,12 +12,15 @@
 # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 # See the License for the specific language governing permissions and
 # limitations under the License.
-import sqlite3
 import struct
 import threading
 
 from synapse.storage.engines import BaseDatabaseEngine
 
+MYPY = False
+if MYPY:
+    import sqlite3
+
 
 class Sqlite3Engine(BaseDatabaseEngine[sqlite3.Connection]):
     def __init__(self, database_module, database_config):