Well, we certainly thought it was a big deal! We were really trying to address this issue of writing stable scripts -- allowing for stable, powerful tooling without ossifying the underlying system. I'm really pleased with the work we did there -- but it's unquestionably one of the more esoteric aspects of DTrace.

Something of a funny story that this brings to mind: the taxonomy we have here is actually the interface taxonomy from what was Sun's Platform Software Architecture Review Committee (PSARC), which itself borrowed it from Sun's larger Software Development Framework (SDF). We had to get DTrace reviewed by PSARC, which we weren't necessarily looking forward to -- in part because of big developments like this one. To get past our PSARC review, we adopted several strategies, one of which was to separate out DTrace from its instrumentation providers as separate cases before the committee. When we first presented DTrace to PSARC, committee members wanted to fixate on instrumentation methodology -- and it was very helpful to be able to defer these fixations to later cases (after having let members pontificate and chew up some of the clock, of course). The other technique that we developed (which was devastatingly effective) was to distract the committee with issues that were irrelevant but amenable to debate. When a debate emerged among the committee members (and PSARC being more or less a debating society, this was practically guaranteed), we would effectively feed both sides of the debate -- and in the end, run out the clock on something we didn't care about. All of this worked exceedingly well -- and DTrace itself (one of the largest cases that had ever appeared before PSARC) was approved with essentially no modifications.

Shortly after the DTrace case was approved, we started bringing forward cases on instrumentation providers. With each case, we presented the stability matrix of that particular provider; on the first such case, I remember vividly one committee member asking: "what the hell is this and when do we review it?!" We explained that it was the stability matrix -- as explained at length in the case that they had in fact already approved. They realized in an instant that they had fixated on a dinghy of nomenclature while we had slipped behind them an ocean liner of semantics -- and it was glorious.