On Jun 21, 2010, at 5:16 PM, Eric Wong wrote: >> overloading the server or hitting memory bandwidth issues. The >> backlog is at the somaxconn default of 128, I'm still not sure if we >> will bump that up or not. > > The default backlog we try to specify is actually 1024 (same as > Mongrel). But it's always a murky value anyways, as it's > kernel/sysctl-dependent. With Unix domain sockets, some folks use > crazy values like 2048 to look better on synthetic benchmarks :)
Somewhat related -- I've been meaning to discuss the finer points of backlog tuning. I've been experimenting with the multi-server socket+TCP megaunicorn configuration from your CDT: http://rubyforge.org/pipermail/mongrel-unicorn/2009-September/000033.html Which I think is what this sentence from TUNING is talking about? "Setting a very low value for the :backlog parameter in “listen” directives can allow failover to happen more quickly if your cluster is configured for it." Our app can catch a batch of requests which will be slow (1-3s), and these can pool on one individual server in our load-balanced EC2 cluster -- exactly the case for the multi-server failover setup. I've put this into production under a healthy load (5000+ RPM) and it appears to work really well! Produces very high requests/s rates at significantly higher concurrency than without, and serves zero 502 errors (part of the goal) I currently I have the unix socket set to a backlog of 64, then failing over to a TCP listener using backlog 1024 (so that things are queued rather than 502'd) I can imagine there might be a case for keeping the TCP backlog low as well & serving errors when overloaded, rather than getting caught in an unrecoverable back-queue tarpit I'm currently failing-over to a dedicated "backup" instance, so that I could measure exactly how much traffic is being offloaded. This means my benchmarks w/o failover are 1 server, but with failover is actually 2 servers. We're reconfiguring to something more like the original diagram at which point I'll do some cluster-wide stress-tests & share data/scripts/process. BTW, this configuration needs a cool name! -jamie http://jamiedubs.com http://fffff.at _______________________________________________ Unicorn mailing list - [email protected] http://rubyforge.org/mailman/listinfo/mongrel-unicorn Do not quote signatures (like this one) or top post when replying
