On Thu, Jan 24, 2008 at 09:58:32AM -0800, Fletcher Cocquyt wrote: > Fellow dtracers - I am diagnosing a busy spamassassin/mailman/sendmail > system - the CPU and memory usage seems normal, but iotop shows I/O and > network are very busy (and initiating TCP connections is quite slow > sometimes (even after tuning the stack)) > > I suspect DNS latency - how can I use Dtrace to quantify latency due to DNS > lookups on this server?
Er, DNS issues don't cause TCP connections to take a long time to complete. DNS issues definitely can cause applications to take a long time to get around to initiating TCP connections. You can use snoop to find DNS requests that are going unanswered, though the "find" part is very manual. Otherwise you can do as Brendan said, and for applications using the resolver directly, you may want to use pid provider probes on res_nsend(). Applications that speak DNS without using the resolver will be more difficult to trace -- you'll have to trace calls to connect/write/read/ sendto/sendmsg/... system calls and figure out how to tell which such calls are interesting based on TCP/UDP port number 53. Nico -- _______________________________________________ dtrace-discuss mailing list dtrace-discuss@opensolaris.org
