2013/12/6 Kohei KaiGai <kai...@kaigai.gr.jp>: > What will happen if sender tries to send a large chunk that needs to > be split into multiple sub-chunks and receiver concurrently detaches > itself from the queue during the writes by sender? > It seems to me the sender gets SHM_MQ_DETACHED and only > earlier half of the chunk still remains on the queue even though > its total length was already in the message queue. > It may eventually lead infinite loop on the receiver side when another > receiver appeared again later, then read incomplete chunk. > Does it a feasible scenario? If so, it might be a solution to prohibit > enqueuing something without receiver, and reset queue when a new > receiver is attached. > Doesn't it an intended usage to attach a peer process on a message queue that had once detached, does it? If so, it may be a solution to put ereport() on shm_mq_set_receiver() and shm_mq_set_sender() to prohibit to assign a process on the message queue with mq_detached = true. It will make the situation simplified.
Regarding to the test-shm-mq-v1.patch, setup_background_workers() tries to launch nworkers of background worker processes, however, may fail during the launching if max_worker_processes is not enough. Is it a situation to attach the BGWORKER_EPHEMERAL flag when your patch gets committed, isn't it? I think it is waste of efforts to add error handling here instead of the core support to be added, however, it makes sense to put a source code comment not to forget to add this flag when it came. Also, test_shm_mq_setup() waits for completion of starting up of background worker processes. I'm uncertain whether it is really needed, because this shared memory message queue allows to send byte stream without receiver, and also blocks until byte stream will come from the peer to be set later. This module is designed for test purpose, so I think it makes more sense if test condition is more corner case. Thanks, -- KaiGai Kohei <kai...@kaigai.gr.jp> -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
