fix: set default mysql isolation level to 'READ COMMITTED' (#30174)

Co-authored-by: Ville Brofeldt <33317356+villebro@users.noreply.github.com>

.gitattributes

@@ -1 +1,2 @@
 docker/**/*.sh text eol=lf
+*.svg binary

superset/config.py

@@ -196,12 +196,14 @@ SQLALCHEMY_DATABASE_URI = (
 # SQLALCHEMY_DATABASE_URI = 'mysql://myapp@localhost/myapp'
 # SQLALCHEMY_DATABASE_URI = 'postgresql://root:password@localhost/myapp'
 
-# The default MySQL isolation level is REPEATABLE READ whereas the default PostgreSQL
-# isolation level is READ COMMITTED. All backends should use READ COMMITTED (or similar)
-# to help ensure consistent behavior.
-SQLALCHEMY_ENGINE_OPTIONS = {
-    "isolation_level": "SERIALIZABLE",  # SQLite does not support READ COMMITTED.
-}
+# This config is exposed through flask-sqlalchemy, and can be used to set your metadata
+# database connection settings. You can use this to set arbitrary connection settings
+# that may be specific to the database engine you are using.
+# Note that you can use this to set the isolation level of your database, as in
+# `SQLALCHEMY_ENGINE_OPTIONS = {"isolation_level": "READ COMMITTED"}`
+# Also note that we recommend READ COMMITTED for regular operation.
+# Find out more here https://flask-sqlalchemy.palletsprojects.com/en/3.1.x/config/
+SQLALCHEMY_ENGINE_OPTIONS = {}
 
 # In order to hook up a custom password store for all SQLALCHEMY connections
 # implement a function that takes a single argument of type 'sqla.engine.url',

superset/initialization/__init__.py

@@ -32,6 +32,7 @@ from flask_session import Session
 from werkzeug.middleware.proxy_fix import ProxyFix
 
 from superset.constants import CHANGE_ME_SECRET_KEY
+from superset.databases.utils import make_url_safe
 from superset.extensions import (
     _event_logger,
     APP_DIR,
@@ -482,12 +483,36 @@ class SupersetAppInitializer:  # pylint: disable=too-many-public-methods
         self.configure_wtf()
         self.configure_middlewares()
         self.configure_cache()
+        self.set_db_default_isolation()
 
         with self.superset_app.app_context():
             self.init_app_in_ctx()
 
         self.post_init()
 
+    def set_db_default_isolation(self) -> None:
+        # This block sets the default isolation level for mysql to READ COMMITTED if not
+        # specified in the config. You can set your isolation in the config by using
+        # SQLALCHEMY_ENGINE_OPTIONS
+        eng_options = self.config["SQLALCHEMY_ENGINE_OPTIONS"] or {}
+        isolation_level = eng_options.get("isolation_level")
+        set_isolation_level_to = None
+
+        if not isolation_level:
+            backend = make_url_safe(
+                self.config["SQLALCHEMY_DATABASE_URI"]
+            ).get_backend_name()
+            if backend in ("mysql", "postgresql"):
+                set_isolation_level_to = "READ COMMITTED"
+
+        if set_isolation_level_to:
+            logger.info(
+                "Setting database isolation level to %s",
+                set_isolation_level_to,
+            )
+            with self.superset_app.app_context():
+                db.engine.execution_options(isolation_level=set_isolation_level_to)
+
     def configure_auth_provider(self) -> None:
         machine_auth_provider_factory.init_app(self.superset_app)
 

tests/integration_tests/superset_test_config.py

@@ -59,9 +59,6 @@ if make_url(SQLALCHEMY_DATABASE_URI).get_backend_name() == "sqlite":
         "removed in a future version of Superset."
     )
 
-if make_url(SQLALCHEMY_DATABASE_URI).get_backend_name() in ("postgresql", "mysql"):
-    SQLALCHEMY_ENGINE_OPTIONS["isolation_level"] = "READ COMMITTED"  # noqa: F405
-
 # Speeding up the tests.integration_tests.
 PRESTO_POLL_INTERVAL = 0.1
 HIVE_POLL_INTERVAL = 0.1

tests/integration_tests/superset_test_config_thumbnails.py

@@ -41,9 +41,6 @@ if make_url(SQLALCHEMY_DATABASE_URI).get_backend_name() == "sqlite":
         in a future version of Superset."
     )
 
-if make_url(SQLALCHEMY_DATABASE_URI).get_backend_name() in ("postgresql", "mysql"):
-    SQLALCHEMY_ENGINE_OPTIONS["isolation_level"] = "READ COMMITTED"  # noqa: F405
-
 SQL_SELECT_AS_CTA = True
 SQL_MAX_ROW = 666