Re: zonelimit issues...

At Tue, 22 Apr 2008 06:35:38 -0700,
Chris Pratt wrote:


On Apr 21, 2008, at 12:43 AM, gnn@xxxxxxxxxxx wrote:

...snip

Well there are plenty of us motivated to get at these issues. Can you
do me a favor and characterize your traffic a bit? Is it mostly TCP,

The traffic that seems to take us out is TCP port 80. I'll make a
generalized guess but it does seem to follow. We freeze on one of
two dramatically heavy use days for our industry (Sunday and Monday
evening). The hang will actually occur on Monday or Tuesday
following these days if sufficient traffic hits us. It has not
always followed this pattern but most frequently. There is always a
high presence of high frequency attacks of various sorts. For
example referer spam posts which hit us hard on our busy
evenings. So it is TCP and I would presume we usually have the
establishment of many useless sessions that could cause us to bump
up against limits and cause exhaustion coupled with our real traffic
peaks.


Interesting, but with TCP it should be easier to tune this, in
particular because TCP has backoff once a packet drops. I gather you
are using facilities, like accept filters, that make it easy to drop
less useful traffic?

This thread has given me several things to try and I'm adjusting (e.g.,
nmbclusters) upward to see what happens.

Sounds good. Using netstat -m and netstat -an are a good way to watch
this issue. -m is the number of mbufs/clusters in use and -an will
show you all sockets, but what you want to check on s the number of
bytes in the recv and send socket buffers, which are the 2nd and 3rd
columns.

I should also mention that this system has the natural limitations
on it's traffic ceiling of two T1s on two NICs and a 3rd LAN NIC
fielding continuous round-robin mysql replication and rsync style
mirroring. It uses two bge interfaces and one server type em
interface. It's always troubled me that the zonelimit issues have
always been associated with higher volume circuits (in what I've
read). But since our issue is very directly related to traffic
levels and seem to occur at times where my monitors show us way over
committed on the two outward facing T1s, I'm still going to proceed
with the adjustments and see if it increases our survivability.

Since zonelimit is a state reached when your system is out of
resources it makes sense that the higher the traffic the sooner you'll
reach it.

Thanks for your time on this.


No problem, it's what I like to do :-)

Best,
George
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