Setting TCP keepalive for Cyrus daemons

[Paul M Fleming]

Shouldn't these client connections already be handled by the poptimeout & 
timeout options?  unless you have it set to zero... 

We have had problems within the murder (old code had several spots where
murder front <-> back communications could deadlock)..

On Sat, 13 Feb 2010, Bron Gondwana wrote:

> On Fri, Feb 12, 2010 at 09:45:02AM -0600, Gary Mills wrote:
> > I've been noticing idle pop3d processes on our Cyrus front end server
> > for some time.  These should be transient.  One that was several days
> > old had an established TCP connection to a wireless client that had
> > disappeared.  Presumably the client never closed the connection.
> > 
> > Setting TCP keepalive on the file descriptor should permit the kernel
> > to close the connection in this situation.  Does this sound
> > reasonable?  Perhaps it's already been addressed in a later Cyrus
> > version.  We're running cyrus-imapd-2.3.8.
> > 
> > I'm willing to add a `keepalive' option to Cyrus master along with the
> > setsockopt() system call to enable that setting.  This option could be
> > added to the cyrus.conf file for any services that could benefit from
> > it. Would this be a reasonable addition to Cyrus?
> 
> This is something I've been wanting to look in to as well.  If a machine
> crashes, it can leave sync_clients hanging for ever, thinking they are
> still talking to the replica - meaning that they hold the lock and
> replication doesn't start back up.  Quite annoying.
> 
> Is there any reason to make it an option rather than just always having
> it on?  Or at least not to make it the default.  If it's a good idea, it
> SHOULD be the default.  I'm strongly against having hundreds of lines of
> config file required to get the sanest defaults!
> 
> Hmm... oh:
> 
> http://tools.ietf.org/html/rfc1122#page-101
> 
>             Implementors MAY include "keep-alives" in their TCP
>             implementations, although this practice is not universally
>             accepted.  If keep-alives are included, the application MUST
>             be able to turn them on or off for each TCP connection, and
>             they MUST default to off.
> 
>             Keep-alive packets MUST only be sent when no data or
>             acknowledgement packets have been received for the
>             connection within an interval.  This interval MUST be
>             configurable and MUST default to no less than two hours.
> 
> Sounds like it does need to be configurable!  Also, the defaults are
> crazy high amounts for a local reliable network.  I think I'd prefer
> about 5 minutes than 2 hours!
> 
> Bron.
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