On Apr17, 2013, at 12:22 , Amit Kapila <amit.kap...@huawei.com> wrote: > Do you mean to say that as an error has occurred, so it would not be able to > flush received WAL, which could result in loss of WAL? > I think even if error occurs, it will call flush in WalRcvDie(), before > terminating WALReceiver.
Hm, true, but for that to prevent the problem the inner processing loop needs to always read up to EOF before it exits and we attempt to send a reply. Which I don't think it necessarily does. Assume, that the master sends a chunk of data, waits a bit, and finally sends the shutdown record and exits. The slave might then receive the first chunk, and it might trigger sending a reply. At the time the reply is sent, the master has already sent the shutdown record and closed the connection, and we'll thus fail to reply and abort. Since the shutdown record has never been read from the socket, XLogWalRcvFlush won't flush it, and the slave ends up behind the master. Also, since XLogWalRcvProcessMsg responds to keep-alives messages, we might also error out of the inner processing loop if the server closes the socket after sending a keepalive but before we attempt to respond. Fixing this on the receive side alone seems quite messy and fragile. So instead, I think we should let the master send a shutdown message after it has sent everything it wants to send, and wait for the client to acknowledge it before shutting down the socket. If the client fails to respond, we could log a fat WARNING. best regards, Florian Pflug -- Sent via pgsql-hackers mailing list (email@example.com) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers