storage.py 文件源码

def set_transaction_isolation_level(session, sqla_txn, connection):
    ''' Set appropriate transaction isolation level.

    Doomed transactions can be read-only.
    ``transaction.doom()`` must be called before the connection is used.

    Othewise assume it is a write which must be REPEATABLE READ.
    '''
    if connection.engine.url.drivername != 'postgresql':
        return

    txn = transaction.get()
    if not txn.isDoomed():
        # connection.execute("SET TRANSACTION ISOLATION LEVEL REPEATABLE READ;")
        return

    data = txn._extension
    if 'snapshot_id' in data:
        connection.execute(
            _set_transaction_snapshot,
            snapshot_id=data['snapshot_id'])
    else:
        connection.execute("SET TRANSACTION READ ONLY;")