On Fri, Jul 10, 2009 at 08:50:29AM -0400, Wietse Venema wrote: > Jakub Nadolny: > > > One SMTP client process was delivering message DF7C21811E53, and > > > that process hangs. > > > > > > THIS IS WHY YOU SEE THE 'DF7C21811E53: SKIPPED, > > > STILL BEING DELIVERED' MESSAGE IN THE LOGFILE. > > > > > > Normally, a watchdog timer will terminate such a process, and the > > > master will log a warning when that happens. The time limit is > > > specified with (main.cf:daemon_timeout, and is 1800s or five hours. > > > > Thank you again. After 4.5 hour message was at last delivered. I would like > > to > > know for the future (as such cases are not so rare): > > 4.5 hours for a 4254293-byte message, that's 260 bytes/second. > This can happen with a slow connection, and with a connection that > is manipulated by a traffic shaping system. > > > 1. What can I do if again SMTP client process will hang? > > Given that the mail arrived after several hours, it seems that the > warning message "still being delivered" was correct, and that the > process was in fact not hanging. > > You can use any number of process inspection tools to see where > a process is. Some examples are: > > # strace -p pid > ... > ^C > # gdb /path/to/smtp pid > (gdb) where > ... > (gdb) detach > > > 3. Does it have connection with Send-Q > 80000 as displayed in netstat as I > > mentioned before? > > You are sending a megabyte file, and some portion of that will be > in the local TCP send queue. If the receiving side reads your data > very slowly, then Postfix network write operations will never time > out, but they will take more time than usual. > > You can check this with tcpdump. The symptoms are a relatively > small TCP window size and a low packet rate. Slow data rates are > a feature of traffic-shaping tools that can be installed in front > of a receiving MTA. Of course slow data rates can also have other > causes. > > tcpdump host xx and port yy > > Postfix is happy as long as it can send a non-zero number of bytes > every $smtp_data_xfer_timeout seconds (180s by default). This limits > the theoretical data rate to 1/180 byte/s. In practice the watchdog > timer will kill the SMTP client.
Thanks a lot! That are great tips to be used. I wish every software has such a good author support as yours. Best Regards, Jakub
