Debugging (Varnish)

An overview of some of the research done in the practice and pedagogy of debugging, as well as some examples of ways that Fastly has addressed issues with debugging Varnish "at scale". A video of this talk is available at https://www.infoq.com/fr/presentations/varnishcon-devon-odell-debugging

Transcript

1. Debugging (Varnish) Devon H. O’Dell | @dhobsd | Fastly | VarnishCon 2016
2. Who am I? Tech Lead, Varnish PFID @ Fastly Personal interest in performance, debugging, concurrency, and introspection. Usually confused about something.
4. Why does debugging matter?
5. The Root of the Problem
6. “Everyone knows that debugging is twice as hard as writing a program in the first place. So if you're as clever as you can be when you write it, how will you ever debug it?” (Brian Kernighan, TEOPS, 1974)
16. “The relationships between debugging success and individual factors … have not been researched… Given that debugging presents challenges for many novices, exploring the influence of self theories on student approaches to debugging appears worthwhile.”
22. sub vcl_recv { if (req.http.answer ~ “^42) { log “enlightened client”; } return vcl_fetch; }
32. Varnish Debugging Tools • varnishlog / varnishtop / varnishncsa / varnishreplay / varnishadm • vcl tracing • crash traces • gdb / lldb • perf / hwpmc
37. locking_function : 25276 threads, 2 locations: cache_foo.c:220 (8); cache_foo.c:210 (25268)
41. Thank you! Devon H. O’Dell | https://9vx.org/ | @dhobsd | https://www.fastly.com