Graceful degradation in overload conditions
wes at umich.edu
Sat Apr 4 13:19:05 EDT 2009
On 04 Apr 2009, at 09:19, Gary Mills wrote:
> What about imapd and pop3d daemons, which also consume resources?
> Are limits a good idea here too? Users will complain to the help
> desk when those limits are reached, of course. Can the msg/shutdown
> file be used to control imapd processes in a nicer manner?
I typically set the lmtpd limits very low, i.e., just above
provisioned demand, because, as you say, inbound mail can queue.
Setting imapd & popd limits at somewhat higher than peek demand
causes a fairly user friendly service degradation: mail delivery more
or less stops, mail reading can continue, but that too will stop
before load is so bad that nothing can be done. I also tend to
actively monitor server load, so in extreme situations I can, e.g.,
stop or severely limit mail delivery or other lesser services to
favor more important services. At some point, tho, you just need to
add more capacity.
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