ashb commented on a change in pull request #19842:
URL: https://github.com/apache/airflow/pull/19842#discussion_r758379886
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File path: airflow/utils/db.py
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@@ -986,3 +988,49 @@ def check(session=None):
"""
session.execute('select 1 as is_alive;')
log.info("Connection successful.")
+
+
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+class DBLocks(enum.IntEnum):
+ """
+ Cross-db Identifiers for advisory global database locks.
+
+ Postgres uses int64 lock ids so we use the integer value, MySQL uses
names, so we use the ``_name_``
+ field.
+ """
+
+ MIGRATIONS = enum.auto()
+ SCHEDULER_CRITICAL_SECTION = enum.auto()
+
+ def __str__(self):
+ return f"airflow_{self._name_}"
+
+
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+def create_global_lock(session, lock: DBLocks, lock_timeout=1800):
+ """Contextmanager that will create and teardown a global db lock."""
+ conn = session.connection()
+ dialect = conn.dialect
+ try:
+ if dialect.name == 'postgresql':
+ conn.execute(text('SET LOCK_TIMEOUT to :timeout'),
timeout=lock_timeout)
+ conn.execute(text('SELECT pg_advisory_lock(:id)'), id=lock.value)
+ elif dialect.name == 'mysql' and dialect.server_version_info >= (5, 6):
+ conn.execute(text("SELECT GET_LOCK(:id, :timeout)"), id=str(lock),
timeout=lock_timeout)
+ elif dialect.name == 'mssql':
+ # TODO: make locking works for MSSQL
+ pass
+
+ yield None
+ finally:
+ # The session may have been "closed" (which is fine, the lock lasts
more than a transaction) -- ensure
+ # we get a usable connection
+ conn = session.connection()
Review comment:
This is the problem and the cause of the failures -- if we close the
connection we can't unlock someone else's lock.
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