Issue with huge numbers of connections
M. Warner Losh
imp at bsdimp.com
Sun Jun 17 19:03:03 UTC 2007
In message: <46757818.5030005 at joeholden.co.uk>
Joe Holden <joe at joeholden.co.uk> writes:
: M. Warner Losh wrote:
: > Greetings,
: > I have a friend who is having problems with a service he's running.
: > He gets billions and billions of connections to this service a day.
: > Somewhere between 10^8 and 10^9 connections, he notices that his
: > servers lose the ability to accept new connections. These are TCP
: > connections.
: > This is with FreeBSD 6.1R. My first question is: does anybody know if
: > the fixes to -current/7.0 have fixed this? Is there a fix that can be
: > back ported? He's currently working around the problem by having a
: > number of different machines that reboot in a round robin fashion, but
: > would like a better solution.
: > Warner
: > _______________________________________________
: Warner, if he hasn't done so already, have you suggested tweaking the
: sysctl variables, such as:
: Tweaking those may help, or he may just be exhausting available
: resources, IIRC its limited to 65k connections per interface, someone
: correct me if I am wrong.
Here's the bug report I got:
There is still a vague problem with the FreeBSD network interface --
especially the part that handles TCP. Something strange happens after
about a week or so (after handling about 10^8 or 10^9
connections). The system becomes unreachable for TCP connections. I
have fixed this problem by having all of the FreeBSD systems reboot
automatically once a week using a cron job. I have not been able to
isolate this issue, but I suspect that there is some kind of problem
with the error handling and some resource gets depleted slowly. I
realize that this is pretty vague, but I have not been able to find
out what actually happens in this case.
I believe that each connection lasts on the order of tens or hundreds
milliseconds, given what I know about the systems in place. My earlier
rephrase omitted a few key points. I suggested that he try to use a newer
version of FreeBSD, but since these are a production system, he's hesitant to
mess with them...
Doing the math on 10^9 connections in a week translates to ~1650/s, so we'd
expect there are on the order of 100-200 connections steady state at any
time. I suspect that the peak load may be up to 100 times that, which is
still only 20000 connections. The hangs don't seem to hang at a peak, but
Given all that, I'm not sure which of the above to try.
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