On Nov 16, 2007 12:36 PM, Sebastian Hagedorn <Hagedorn@xxxxxxxxxxxx> wrote:I just had a discussion with a colleague regarding this. He made two observations: 1. In the absence of the SO_KEEPALIVE option it is entirely possible that a TCP connection remains ESTABLISHED even when the other side has gone.I said that socket should timeout, but this is true only when the protocol (TCP here) require a response (usualy AK here) or at connection establishement.
Right.
On the contrary it should stay open indefinitely util something happens. Router doing NAT can drop a too old connection, because it has to maintains a NAT table and make some cleanup time to time, this where "KEEPALIVE" become usefull.
Not only there, but I think also in the case of unilaterally dropped connections.
This may not be a solution to this particular problem, but it made me wonder why Cyrus does *not* use SO_KEEPALIVE. Is there a downside to it?Cyrus has already a built-in time out, it seems a lite conflicting to actively maintains the connection until it drop it itself !
I'm not sure I understand that sentence.
This is the works of the client to actively maintains the connection, if it want it !
Yes, but what if the client is gone? I realise that *normally* the server keeps a built-in timeout, but I'm guessing that sometimes it doesn't work, perhaps because something (in prot_fill() perhaps?) blocks.
I think I will try one more approach: I reverted cyrus.conf to not use "-U 1" anymore, so that processes should be reused. I will strace one of the pop3d processes in the hope that it gets stuck. That way I should be able to see where things go wrong. If the process terminates normally I will try with another one. If that doesn't go anywhere, I guess I'll drop thisYou could try to replace imapd by a home made script, something like . mv imapd imapd_ echo exec strace -o /tmp/imapd.$$ imapd_ $* > imapd chmod imapd a+x
Thanks for the suggestion. I'll think about it, although I'm wary of doing that on a production server.
investigation. We will upgrade to RHEL 5 some time next year, so hopefully that will bring new bugs :-)Sorry but I dont understand what you are complaining about!
I'm not complaining ...
Is-it because the imap or pop client is loosing its connection and this disturb the user
No.
or just because you are getting some sleeping processes ?
If it were "some" I wouldn't worry. I'm talking hundreds of processes! I know I can kill them, in fact for the pop3d processes we run this command once a month:
ps -C pop3d -o pid,start|grep [a-z]|awk '{print $1}'|xargs kill
(It kills pop3d processes that have the month in their start time, i.e. are
more than a day old)
But for imapd processes it's not as easy to tell if they are just long-living or stuck.
Do you have a "timeout" option in your imapd.conf to force the imap/pop server to autologout ?
No. But both POP and IMAP have default timeouts. They just don't work in my case.
--
.:.Sebastian Hagedorn - RZKR-R1 (Gebäude 52), Zimmer 18.:.
Zentrum für angewandte Informatik - Universitätsweiter Service RRZK
.:.Universität zu Köln / Cologne University - ✆ +49-221-478-5587.:.
.:.:.:.Skype: shagedorn.:.:.:.Attachment:
pgpLgzm1j25Ec.pgp
Description: PGP signature
---- Cyrus Home Page: http://cyrusimap.web.cmu.edu/ Cyrus Wiki/FAQ: http://cyrusimap.web.cmu.edu/twiki List Archives/Info: http://asg.web.cmu.edu/cyrus/mailing-list.html
