Wandering Thoughts archives


Some thoughts on how I still miss DTrace (and also mdb)

Although I'm generally happy with our Linux fileservers, every so often we run into an issue where I miss OmniOS's DTrace and mdb; DTrace for dynamic visibility into what the system was doing, and mdb for static inspection and tracing through kernel data structures. In theory Linux has equivalents of both of these. In practice this Linux future is unevenly distributed. It's likely that our Linux fileservers will have great visibility once we upgrade them to Ubuntu 22.04 in 2022 or 2023, but it's taking some time to get there. This is in stark contrast to Solaris, where DTrace (and mdb) were usable from the very beginnings of our ZFS fileservers, very shortly after Solaris 10 included DTrace at all.

It's my feeling that this difference is ultimately because of how Solaris was developed as a unitary whole by Sun, a single organization, in contrast to how Linux's performance and observability systems have been developed in many separated pieces by different groups. Since there was a single organization controlling all Solaris development, people within Sun were in a position to set overriding priorities and decide that DTrace was a good enough idea that it would be finished and shipped all at once in a ready to go state. Since Solaris was a unitary system, the kernel and user tools could ship together as a coordinated thing and the same people could develop both together.

(Similar things apply for mdb, which needs to move in step with the kernel.)

I do feel that the Linux approach has had some important advantages, but it's undeniable that it's been slower to produce actual results (and those results are unevenly distributed, depending on how up to date your version of Linux is and how rapidly it incorporated various things). My perception is that there's been a back and forth where people put forward needs and prototypes, the kernel adds facilities, people build tools that use and push those facilities, and the usefulness of these tools pushes the kernel forward. Some of these tools have wound up being superseded or abandoned, and the overall selection of tools (and facilities) isn't unified. Since the overall Linux system is not a unified thing under the control of one organization, no one in Linux could write an engineering white paper, build a prototype, or otherwise line up everyone behind one thing to get it done rapidly and out into the world all at once.

In a way, this is what I miss from DTrace and mdb. Solaris could move decisively, for better or worse (and to some extent Illumos still can). Not all of its decisive moves were wins (ask me what I feel about SMF), but there was a real power in its ability to make them, and DTrace is a great illustration of that.

PS: It feels possible that not making a public, supported interface between dtrace and the kernel was one of the things that allowed DTrace as a whole to be shipped early, since it reduced the number of public things that had to be carefully designed and tested. This is another area where having a unitary system helps in several ways.

solaris/DTraceStillMiss written at 23:52:33; Add Comment

The death and life of postmaster@anywhere

A decade ago I wrote The quiet death of postmaster@anywhere, where I proclaimed that the postmaster@ address was dead, killed by steadily increasing spam volume (and decreasing actual use). I was recently reminded of that entry and, a decade later, I have to sort of take back what I wrote. It's true that postmaster addresses are increasingly dead, but when they are it's not for the reasons that I thought back then.

Perhaps ten years ago our postmaster account got a bunch of spam and bounces (I can no longer remember, but what I wrote in my old entry suggests that it may have at the time). These days it doesn't; we get basically no bounces that I can see, and very little spam (and almost all of the spam is recognized and rejected immediately). It's possible that this experience is far from universal, but I can think of some reasons why it might be. And in more anecdotal data, my spam-trap SMTP server has seen only one email to its postmaster address from 2017 onward.

(One potential reason for less spam to postmaster@ addresses is an increased difficulty in sending spam and along with it, an increased professionalization of spam sending. Spamming postmaster addresses is not very productive, so if spamming resources are limited and cost spammers things I'd expect to see less of it.)

But that doesn't mean that sending email to postmaster@ addresses will do you any good these days, or even work. What I've observed from sending the occasional spam complaint is that more and more places seem to be no longer accepting email to postmaster@ and sometimes even abuse@ addresses. I doubt this is driven by spam volume; instead I rather think it's a deliberate policy choice by places, especially by large email providers. Even when email to postmaster@ 'works' for large places, it's probably not reaching the technical people who deal with the mail system, or even necessarily the abuse handling people. It's probably much more likely to drop into some sort of general support system, with the attendant low odds of getting prompt or effective attention.

Of course in one sense this is nothing new. It's been years since sending email to any well known or public address got you useful results with large places (for either spam complaints or technical problem reports). The only real difference these days is you might get an actual SMTP rejection that says your email to postmaster@ or abuse@ is not accepted, instead of your email just quietly disappearing.

But for many smaller and more modest places, I suspect that postmaster@ is still alive. It certainly is here, and even for the overall university email system.

spam/PostmasterIsDeadII written at 00:28:01; Add Comment

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