Great deck! In particular, for the incredible magic on slide 14, a debt of thanks is owed to John Levon[1] and to whomever has maintained that work and brought it forward.
On slide 28, the presentation asks "What is 'Speculative Tracing'?" It's unclear if that's a rhetorical question, but just to answer it here: speculative tracing is a DTrace facility that allows for data to be traced speculatively, and only committed to the trace buffer if and when some other (later) condition is met.[2] My original inspiration for this was a case that we had back in the day at Sun on the Performance and Application Engineering (PAE) team, when Yufei Zhu (now at Facebook) described a case she had in which one out of every 10,000 mmap()'s was failing with EINVAL -- and it was really tough to use DTrace when she was only interested in its output 0.01% of the time. For Yufei's (motivating) example, speculative tracing offered a way of capturing all of the necessary data on every mmap request, but only emitting that data when the entire operation was found to have failed. Speculative tracing is one of those you-don't-need-it-until-you-need-it features of DTrace (to which I would certainly add anonymous tracing) -- but when you need it, it's a lifesaver, and I have it used it as recently as last week to nail a particularly nasty bug that very much needed it.[3]
On slide 28, the presentation asks "What is 'Speculative Tracing'?" It's unclear if that's a rhetorical question, but just to answer it here: speculative tracing is a DTrace facility that allows for data to be traced speculatively, and only committed to the trace buffer if and when some other (later) condition is met.[2] My original inspiration for this was a case that we had back in the day at Sun on the Performance and Application Engineering (PAE) team, when Yufei Zhu (now at Facebook) described a case she had in which one out of every 10,000 mmap()'s was failing with EINVAL -- and it was really tough to use DTrace when she was only interested in its output 0.01% of the time. For Yufei's (motivating) example, speculative tracing offered a way of capturing all of the necessary data on every mmap request, but only emitting that data when the entire operation was found to have failed. Speculative tracing is one of those you-don't-need-it-until-you-need-it features of DTrace (to which I would certainly add anonymous tracing) -- but when you need it, it's a lifesaver, and I have it used it as recently as last week to nail a particularly nasty bug that very much needed it.[3]
[1] https://blogs.oracle.com/levon/entry/python_and_dtrace_in_bu...
[2] http://dtrace.org/guide/chp-spec.html
[3] https://twitter.com/bcantrill/status/769225926726918144