I've written before about the minimal set of metrics that can serve effectively as application/service vital signs. One such set is the RED acronym, which stands for Request Rate, Request Errors, and Request Duration. (I'll write in the future about what's missing from this acronym, but it'll serve the purpose for now).
Earlier today, Baron Schwartz hosted a live webinar that took a deep look at percentiles and their role in performance monitoring. This is a tricky, engaging subject: as Baron wrote in a blog post last year, "Customers ask us for p99 (99th percentile) of metrics pretty frequently" -- but percentiles often don't work the way many people think.
You can access a recording of today's webinar here, where Baron returned to that subject and illuminated many of the finer points of percentiles, this time examining why people ought to be careful around percentiles and how people can best use them to their advantage.