ashb commented on a change in pull request #10956:
URL: https://github.com/apache/airflow/pull/10956#discussion_r499878674
##########
File path: airflow/utils/sqlalchemy.py
##########
@@ -141,3 +142,107 @@ def skip_locked(session: Session) -> Dict[str, Any]:
return {'skip_locked': True}
else:
return {}
+
+
+def nowait(session: Session) -> Dict[str, Any]:
+ """
+ Return kwargs for passing to `with_for_update()` suitable for the current
DB engine version.
+
+ We do this as we document the fact that on DB engines that don't support
this construct, we do not
+ support/recommend running HA scheduler. If a user ignores this and tries
anyway everything will still
+ work, just slightly slower in some circumstances.
+
+ Specifically don't emit NOWAIT for MySQL < 8, or MariaDB, neither of which
support this construct
+
+ See https://jira.mariadb.org/browse/MDEV-13115
+ """
+ dialect = session.bind.dialect
+
+ if dialect.name != "mysql" or dialect.supports_for_update_of:
+ return {'nowait': True}
+ else:
+ return {}
+
+
+def nulls_first(col, session: Session) -> Dict[str, Any]:
+ """
+ Adds a nullsfirst construct to the column ordering. Currently only
Postgres supports it.
+ In MySQL & Sqlite NULL values are considered lower than any non-NULL
value, therefore, NULL values
+ appear first when the order is ASC (ascending)
+ """
+ if session.bind.dialect.name == "postgresql":
+ return nullsfirst(col)
+ else:
+ return col
+
+
+USE_ROW_LEVEL_LOCKING: bool = conf.getboolean('scheduler',
'use_row_level_locking', fallback=True)
+
+
+def with_for_update(query, **kwargs):
Review comment:
Done in
https://github.com/apache/airflow/pull/10956/commits/8f357fdf4630df47d4639706516733e0587480dd
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