def obtain_transaction_lock(session: Session, lock_space: Optional[str],
lock_value: int) -> None:
"""Obtain a transaction-level advisory lock from PostgreSQL.
The lock_space arg must be either None or the name of one of the members of the
LockSpaces enum (case-insensitive). Contention for a lock will only occur when both
lock_space and lock_value have the same values.
"""
if lock_space:
try:
lock_space_value = LockSpaces[lock_space.upper()].value
except KeyError:
raise ValueError("Invalid lock space: %s" % lock_space)
session.query(func.pg_advisory_xact_lock(lock_space_value,
lock_value)).one()
else:
session.query(func.pg_advisory_xact_lock(lock_value)).one()
def lock_table(connection: Connection, target_table: Table):
"""
Lock a table using a PostgreSQL advisory lock
The OID of the table in the pg_class relation is used as lock id.
:param connection: DB connection
:param target_table: Table object
"""
logger.debug('Locking table "%s"', target_table.name)
oid = connection.execute(
select([column("oid")]).select_from(table("pg_class")).where(
(column("relname") == target_table.name))).scalar()
connection.execute(select([func.pg_advisory_xact_lock(oid)])).scalar()
def lock_table(connection: Connection, target_table: Table):
"""
Lock a table using a PostgreSQL advisory lock
The OID of the table in the pg_class relation is used as lock id.
:param connection: DB connection
:param target_table: Table object
"""
logger.debug('Locking table "%s"', target_table.name)
oid = connection.execute(select([column("oid")])
.select_from(table("pg_class"))
.where((column("relname") == target_table.name))
).scalar()
connection.execute(select([func.pg_advisory_xact_lock(oid)])).scalar()