On Mon, 10 Mar 2014, Marco wrote:
> My server is:
> Red Hat Enterprise Linux Server release 6.3 (Santiago)
> Without problems I read something like this:
>
> total used free shared buffers cached
> Mem: 8061976 7651020 410956 0 1355964 3412788
> -/+ buffers/cache: 2882268 5179708
> Swap: 4194296 32180 4162116
>
> procs -----------memory---------- ---swap-- -----io---- --system--
> -----cpu-----
> r b swpd free buff cache si so bi bo in cs us
> sy id wa st
> 2 0 32180 386880 1356476 3423712 0 0 643 327 25 18
> 10 4 81 5 0
Those numbers look okay. Obviously more memory is nice for caching disk
I/O, but you're doing fine.
> current cyrus.conf:
> SERVICES {
> # add or remove based on preferences
> imap cmd="imapd" listen="imap" prefork=5
> pop3 cmd="pop3d" listen="pop3" prefork=3
> sieve cmd="timsieved" listen="sieve" prefork=0
> lmtp cmd="lmtpd -a" listen="lmtp" prefork=0
> }
>
> I have to prevent memory issue when some oddity forces clients to make
> DOS on Cyrus. So I would like to configure the maxchild cyrus
> parameter for imap. I would like to set this value to avoid memory
> issue during normal work, having a known value of system RAM.
Here is what I'm using on a Cyrus backend with 8GB of RAM:
imap cmd="/usr/local/cyrus/bin/imapd" listen="imap" proto="tcp4" prefork=10 maxchild=4000
imaps cmd="/usr/local/cyrus/bin/imapd -s" listen="imaps" proto="tcp4" prefork=10 maxchild=1000
sieve cmd="/usr/local/cyrus/bin/timsieved" listen="sieve" proto="tcp4" prefork=0 maxchild=100
lmtp cmd="/usr/local/cyrus/bin/lmtpd" listen="lmtp" proto="tcp4" prefork=1 maxchild=100
I tuned the maxchild setting to balance our usage patterns between the
imap and imaps ports. Our highest open connection count is about 1500
total, so there is quite a bit of headroom.
> I see that an IMAPD process takes in average 22-25MB. With 8GB RAM,
> the server would swap already with less than 400 conns; it not
> happens, so this evaluation is wrong or too many conservative. I think
> that I better consider differences between RSS and SHR memory to
> tuning imapd processes number, but I'm not sure.
>
> Could you help me in this tuning? In particular I'm interested on
> relation between memory usage and maxchild imapd processes.
I'm running a Cyrus Murder cluster with separate frontends and backends,
so my numbers won't directly correlate. On a backend with about 700 imapd
processes, I have the following memory usage:
total used free shared buffers cached
Mem: 8200092 8136084 64008 0 2735124 1614016
-/+ buffers/cache: 3786944 4413148
Swap: 1951736 36544 1915192
> Meanwhile I would also tune the maxfds parameter. With lsof I measure
> about 60 opened files by each imapd process. If I have 400 imapd
> processes it means a 'ulimit -f' global system of 60*400=24000. This
> is wrong, because I currently have a 4096 limit and I never had
> problems. Maybe do I have to consider only 'Running' processes to
> compute this treshold?
My Cyrus init script does:
# Crank up the limits
ulimit -n 209702
ulimit -u 4096
ulimit -c 102400
This particular backend has:
root@cyrus-be1:~# cat /proc/sys/fs/file-nr
25696 0 819000
Again, this is with about 700 imapd processes.
Andy
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