A uprobes addendum

While I really like systemtap and wish it, or something like it, could be integrated, this is not the most compelling use case one could come up with. 'Who has the largest ps(1) SWAP column' and 'who has most PostgreSQL connections' are not obviously related, and I can't imagine anyone thinking that the same tool should be able to answer both questions (not least since the first question can easily be answered *now*).

However, questions like 'why is my PostgreSQL backend suddenly spending most of its time doing IPC to nothing obvious' are basically impossible to answer now without killing the backend and hacking the source code, which would tend to perturb the answer because whatever perturbation of dynamic state was causing this would necessarily be lost when the process was restarted. With systemtap/dtrace annotations and a few taps in easy (even for kernel idiots like me) to figure out places in the kernel, it was trivial to answer.