RailsConf slides

Posted by Nick Sieger Sat, 31 May 2008 23:42:00 GMT

If you already saw my JavaOne slides, these aren’t too different, but I think they’re better and prettier, too.

JRuby at RailsConf

Get them here.

Update. The slides are pretty lean on explanation. Just in case you’re confused, the narrative goes like this:

  • What’s your deployment nirvana look like? (various existing options)
  • With JRuby, you can deploy Rails applications in a single operating system process instead of many.
  • However, there are a few configuration changes needed to accomodate JRuby. (Steps for converting existing apps, configuration code snippets.)
  • Now, JRuby-Rack helps with the configuration, because all of the logging/session/public path re-jiggering is taken care of for you. It’s now bundled with Warbler as of version 0.9.9.
  • Performance is good and getting better. You can scale up the number of requests you can handle really easily just by setting the number of runtimes to create inside Warbler’s config/warble.rb file.
  • Lots of new stuff is happening right now to make Rails better. JRuby will be able to leverage these changes and become an even more desirable deployment platform. Stay tuned!

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JRuby Hackfest at RailsConf

Posted by Nick Sieger Thu, 22 May 2008 15:40:00 GMT

Thanks to our friends at LinkedIn, Joyent and Sun, we’re having a hackfest at McMenamins/Kennedy School on Thursday evening, May 29, starting at 6:30pm, complete with food and beverages!

Do stop by and hang out with us! Leave a comment over at Charlie’s announcement if you’re interested in joining us.


Kennedy School
Local: (503) 249-3983
Elsewhere: (888) 249-3983

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JavaOne slides

Posted by Nick Sieger Thu, 08 May 2008 22:02:39 GMT

For those of you interested in the content of my talk at JavaOne this morning, here are the slides.

(They’re not quite the version I used in the talk -- just the readable, context-free, usable bits.)

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Introducing JRuby-Rack

Posted by Nick Sieger Thu, 08 May 2008 17:31:00 GMT

Continuing in the spirit of Conference-Driven Development, I’m happy to announce the first public release of JRuby-Rack! You can use it to run Rails, Merb, or any Rack-compatible application inside a Java application server.

Also released today is Warbler 0.9.9, which has been updated to bundle JRuby-Rack.

In addition to providing as seamless a connection as possible between the servlet environment and Rack, JRuby-Rack (along with Warbler) is also bridging the gap between Ruby and Java web development. Some of the things it does are:

  • Makes the Java servlet context and servlet request available to Ruby through special variables in the Rack environment
  • Servlet request attributes from Java are passed through and available in the Rack environment. Request attributes can override Rack variables such as PATH_INFO, QUERY_STRING etc.
  • Configures Rails deployment options such as page caching directories and session handling automatically and optimally for the servlet environment.

I’ve also included the beginnings of some extensions that should help integrate Rails with existing Java web frameworks, servlets, JSPs, and other code. For example, you can invoke a Rails request from within a JSP with a tag:

<jruby-rack:rails path="/projects/activity" params="layout=none"/>

You can set servlet and session attributes and forward to other servlets and JSPs from your Rails controllers:

class DemoController < ApplicationController
  def index
    servlet_request["hello"] = "world!"
    session["rails"] = "Visible to java!"
    forward_to "/attributes.jsp"

and read them from within the servlet or JSP:

  <dt><tt>servlet_request["hello"] | request.getAttribute("hello")</tt></dt>
  <dd><%= request.getAttribute("hello") %></dd>
  <dt><tt>session["rails"] | session.getAttribute("rails")</tt></dt>
  <dd><%= session.getAttribute("rails") %></dd>

This is just the beginning of this kind of integration, and I’m interested where people take it. I think this provides a nifty way to start integrating Rails bits into existing applications or reuse existing Java web application code.

I’ve tagged the release with an 0.9 version number. I believe the bits are ready for serious use, but could use some help pounding out a few more bugs before calling it 1.0. So jruby -S gem install warbler today, try it out, and bring plenty of feedback to the JRuby user list!

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Spring and Summer Gigs

Posted by Nick Sieger Fri, 18 Apr 2008 17:25:16 GMT

Just a quick note on some upcoming gigs. I’ll be speaking next month at both JavaOne and RailsConf, giving an update on the JRuby deployment situation, which by the way is rapidly improving! Despite my proposal for a hands-on tutorial on JRuby deployment not getting accepted for RailsConf, I’ve been asked to fill one of the Sun-sponsored talk slots again. So, much like RailsConf EU last fall, if you come listen I promise you will not get a heavy sales pitch from me! Do stop by, I may even have a couple goodies in store for you.

I also feel privileged to be speaking at RubyFringe this summer, where I haven’t yet determined exactly what I’ll be talking about (although it will probably have some connection to JRuby).

Hope to see you at one of these upcoming events!

Update: We just re-jiggered the schedule of 3 JRuby-related talks at JavaOne, including mine, so that they flow better from beginning to end of the week. My talk is now on Thursday morning instead of Wednesday morning. In addition, Charlie and Tom’s is on Tuesday, and Ola’s is on Wednesday. If you’re attending JavaOne and are interested in JRuby-related talks, please make sure you log into Schedule Builder and re-check your schedule.

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ImageVoodoo 0.1 Released

Posted by Nick Sieger Thu, 27 Mar 2008 21:39:23 GMT

Introducing ImageVoodoo

I just pushed out the first release of ImageVoodoo, a nifty little image manipulation library conceived as a quick hack by Tom. It’s a play-on-words of ImageScience, of course, the quick, lightweight imaging library for Ruby. To get it,

jruby -S gem install image_voodoo

What’s cool about ImageVoodoo (other than the name) is that we were able to make it API-compatible with ImageScience. In fact, ImageVoodoo’s image_science.rb simply looks like this:

require 'image_voodoo'
# HA HA...let the pin-pricking begin
ImageScience = ImageVoodoo

So, you can use it pretty much anywhere you might use ImageScience, and it should just work. At work, we’re using it with attachment_fu, and it works great. ImageVoodoo even steals and uses ImageScience’s unit tests (which all run successfully, too). Speed-wise, it’s about twice as slow as ImageScience running on MatzRuby, but still plenty fast enough for most cases.

But we wouldn’t be having fun unless we embraced and extended a little bit, right? So I added a couple of extra features you might find useful.


Since ImageVoodoo is just leveraging the Java Platform’s imaging libraries, image rendering can be easily tied into a simple preview frame. This code:

ImageVoodoo.with_image("samples/checkerboard.jpg") do |img|

Will pop up a little frame like this:


The code that displays the preview frame is nice and compact, and shows off how nicely you can write clean swing GUI code using JRuby’s java integration features.

class ImageVoodoo
  class JImagePanel < javax.swing.JPanel
    def initialize(image, x, y)
      @image, @x, @y = image, x, y
    def paintComponent(graphics)
      graphics.drawImage(@image, @x, @y, nil)

  class WindowClosed
    def initialize(block = nil)
      @block = block || proc { java.lang.System.exit(0) }
    def method_missing(meth,*args); end
    def windowClosing(event); @block.call; end

  def preview(&block)
    frame = javax.swing.JFrame.new("Preview")
    frame.add_window_listener WindowClosed.new(block)
    frame.set_bounds 0, 0, width + 20, height + 40
    frame.add JImagePanel.new(@src, 10, 10)
    frame.visible = true


As I was fixing a bug in ImageVoodoo’s file saving I whipped up a little command-line utility to aid debugging. It allows you to string along several image manipulation actions on a single command-line. For example,

jruby -S image_voodoo --push --resize 50x50 --preview --save t1.jpg \
  --pop --resize 40x40 --preview --save t2.jpg \
  --pop --resize 30x30 --preview --save t3.jpg image.jpg

This will resize image.jpg into three smaller images, t[1-3].jpg, but will pop up a preview frame at each step of the way. Simply close the preview frame to continue to the next action, or quit out of the application to abort.


And so, another functional area, image manipulation, becomes as easy on JRuby as it is on MatzRuby. Now that fancy social networking application you’ve been working on should have one less reason to be able to run unmodified on JRuby!

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Monkey-patching is Part of the DIY Culture

Posted by Nick Sieger Fri, 14 Mar 2008 00:07:00 GMT

Recently there was a long (122 posts!) thread on Ruby-talk started by Avdi Grimm (based on a post he made on his blog). He took a risk by titling the post “Monkey-patching is Destroying Ruby,” which got a lot of attention but probably ruffled a few too many feathers before he had a chance to justify his argument.

I don’t disagree with Avdi’s main point, which is that monkey-patching isn’t always the best tool for the job. But I contend that it’s still a basic part of the Ruby programming culture, like it or not. I believe the reason for this is that monkey-patching is an extremely empowering technique. It’s part and parcel of the hacker/DIY culture.

Anyone who has had an experience in a less-flexible language or caught in a hard place trying to debug a closed-source library can appreciate how liberating it is to take matters into your own hands, fix your own problem, and to be able to do it without modifying the original library source. It’s a revelatory experience that makes you never want to go back to inflexible programming environments ever again. There’s also nothing wrong with monkey-patching a library you don’t control as long as you freeze all the code you’re using before making a working patch -- if your patch works and you don’t change or upgrade anything, you’re not likely to encounter any problems.

Of course all monkey-patches are not created equal. Some are certainly more onerous than others. Let me give you an example I ran into myself recently, which raises some questions for which I don’t yet have the answer myself.

The most prolific Rick Olson’s popular plugin attachment_fu uses Ruby’s tempfile library. It has a legitimate need to extend Tempfile to preserve the file extension on tempfiles, so that image conversion routines can use the file extension to help identify the format. How it accomplishes this, however, is not very pretty. Here’s the original Ruby code (as of Ruby 1.8.6 p111):

def make_tmpname(basename, n)
  sprintf('%s.%d.%d', basename, $$, n)
private :make_tmpname

Seems like about as reasonable a place as any to hook in, right? But the method is marked private -- I’m guessing the original implementor (according to svn blame, it appears to be Akira Tanaka) probably did not intend for the method to be replaced. But, hey, it’s Ruby, right? So away attachment_fu goes:

Tempfile.class_eval do
  # overwrite so tempfiles use the extension of the basename.  important for rmagick and image science
  def make_tmpname(basename, n)
    ext = nil
    sprintf("%s%d-%d%s", basename.to_s.gsub(/\.\w+$/) { |s| ext = s; '' }, $$, n, ext)

As far as monkey-patches go, this isn’t too bad. There is no code copied from the original implementation, and it’s a fairly focused and compact method. The fact that it’s private is a bit of a smell, though. But, it works, and we forget about it happily (if we even knew it existed in the first place), and hope that tempfile.rb never changes.

Well, in my case, it did. MenTaLguY has been working on more robust, thread-safe versions of the standard libraries. And he changed the arity of make_tmpname:

@@sequence_number = 0
@@sequence_mutex = Mutex.new
def make_tmpname(basename)
    File.open("/dev/urandom", "rb") do |random|
    # insecure fallback
    sequence_number = @@sequence_mutex.synchronize { @@sequence_number += 1 }

Resulting in:

Read error: #<RuntimeError: cannot generate tempfile `': wrong number of arguments(1 for 2)>
/Users/nicksieger/Projects/jruby/trunk/jruby/lib/ruby/1.8/tempfile.rb:39:in `initialize'
/Users/nicksieger/Projects/jruby/trunk/jruby/lib/ruby/gems/1.8/gems/mongrel-1.1.3-java/lib/mongrel/http_request.rb:47:in `new'
/Users/nicksieger/Projects/jruby/trunk/jruby/lib/ruby/gems/1.8/gems/mongrel-1.1.3-java/lib/mongrel/http_request.rb:47:in `initialize'
/Users/nicksieger/Projects/jruby/trunk/jruby/lib/ruby/gems/1.8/gems/mongrel-1.1.3-java/lib/mongrel.rb:149:in `new'
/Users/nicksieger/Projects/jruby/trunk/jruby/lib/ruby/gems/1.8/gems/mongrel-1.1.3-java/lib/mongrel.rb:149:in `process_client'
/Users/nicksieger/Projects/jruby/trunk/jruby/lib/ruby/gems/1.8/gems/mongrel-1.1.3-java/lib/mongrel.rb:285:in `run'

So, it took me a while before it occurred to me that something in my project might be overriding make_tmpname. But even after I found it, notified MenTaLguY, and he fixed it, it still left me wondering: who’s in the wrong here? Akira-san, for not making a better way to hook into make_tmpname, Rick for monkey-patching it, or MenTaLguY for changing the method arity in his rewrite? I can’t really point the blame at any of them.

There are certainly more egregious and offensive monkey-patches than this example (and I include myself in that camp). In any case though, I could live with just about any monkey-patch if I had better debugging tools. For example, it would be great if you could ask Ruby to track and retain references to all methods, including those that get replaced, along with the source locations where each was defined. Another possibility might be a before_method_added hook that could let you track method replacements as they’re about to happen (and maybe even veto method redefinitions!).

These are the types of tools that an enterprising Ruby programmer could look at adding to any one of the existing Ruby implementations. Both JRuby and Rubinius are becoming test beds for bleeding edge features that could help advance the state of the art. So pitch in and help make monkey-patching less painful!

Postscript: This post coming to you from the Illinois interstate courtesy of Curt and his 3G EVDO wi-fi hub!

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JRuby and the Permanent Generation

Posted by Nick Sieger Thu, 21 Feb 2008 05:52:44 GMT

One of the aspects we have to work around building and improving a dynamic language implementation on the Java Virtual Machine is the way the JVM loads and executes bytecode. In order for JRuby to take advantage of the Hotspot just-in-time (JIT) compiler, JRuby needs to generate Java bytecode at runtime, during execution of Ruby code. If that bytecode gets executed often enough and meets certain other rather mysterious conditions, Hotspot will turn it into machine code.

Unfortunately the VM was originally designed to run one language well, and that’s Java. The only way to get bytecode loaded into the JVM is through the Java class loader. With Java, most if not all the code is compiled to bytecode ahead of time and the VM assumes (and optimizes) for the fact that classes will not be shuffled around in memory. Partly due to these assumptions, the JVM stores bytecode along with other class metadata in a separate heap called the “permanent generation”, or just “permgen”. (I’m guessing the name “permanent” was used because originally objects in this heap were probably not garbage collected).

However, because JRuby needs to provide the amount of dynamism that a Ruby programmer would expect (open classes; modules included; methods added/removed at any time), a Ruby class does not cleanly map one-to-one with a Java class. Instead, it’s easier to think of Ruby classes as method-bags. As a result, JRuby creates a new Java class for every Ruby method that it decides to compile down to bytecode. Additionally, since Ruby methods can come and go, in order for the method to be collectible by the garbage collector, it needs to live in its own class loader.

Of course, JRuby is not the first Java program to generate classes and load them at runtime (JSPs have been doing this for ten years). But it may create more class and class loader garbage than just about any program ever run on the JVM. For small programs, generating a class per method would be no big deal, but consider a Rails application: The Rails codebase itself has thousands of methods, but it also generates plenty of new methods at runtime.

Consider a non-trivial Rails application that makes liberal usage of the Ruby standard library, and also uses a handful of plugins, and the number of methods available for JRuby to compile can easily exceed 10,000. If the average overhead of a single JRuby method class is around 8K (varying due to method size, of course), this would occupy up to 80 megabytes of permgen space. (By contrast, the JVM’s default size of the permgen space is 64 megabytes, so we’re already over the limit). Now consider that, with Goldspike we need to use multiple JRuby runtimes in order to achieve concurrent requests due to Rails’ lack of thread-safety, and the number is multiplied further. If you were to deploy 4 Rails applications each with 4 active runtimes into a single application server, you’re looking at almost 1.2 gigabytes of permgen space necessary to run your applications! (Usually, it’s common to run multiple applications in a Java application server, but with Rails applications that may need to be reconsidered.)

Because of this multiplicative cost, shortly after JRuby 1.1RC1 was released we took the somewhat drastic measure of capping the number of methods that each runtime would JIT-compile to 2048. But after a while it became obvious even with a threshold-based approach, JRuby was still wasting a ton of permgen space with duplicate copies of compiled methods. So for 1.1RC2 we introduced a JIT cache that could be set up to be shared among multiple runtimes.

The figure below shows the effect. Under consideration is a single JRuby/Rails/Goldspike application deployed in Glassfish, with varying numbers of runtimes, right after deployment (cold) and after some warmup to load more Rails code and allow JIT to reach the method threshold. JRuby trunk revision 5545 had the 2K JIT threshold, but not the sharing. Revision 5931 is right before RC2 was released, with the method cache wired up. (We also took some measures to reduce permgen consumption in those 500 revisions, so some of that is visible as well.)


The just-released Goldspike 1.5 will use this shared method cache by default, so all you’ll have to do is upgrade to receive the benefits. An easy way to do that is to install Warbler 0.9.3, an update which bundles Goldspike 1.5 and JRuby 1.1RC2.

These kind of techniques to reduce JRuby’s permgen overhead are only going to go so far when the underlying VM still isn’t expecting to be abused in this way. That’s why we’re looking forward to a JRuby that will be able to take advantage of proposed future enhancements like anonymous classes/method handles as part of John Rose’s Da Vinci Machine project. For more information along those lines, head over to Charlie’s discussion of what comes next.

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Screencast: RSpec and NetBeans

Posted by Nick Sieger Fri, 08 Feb 2008 15:13:16 GMT

A new screen cast is up with yours truly showing off NetBeans’ RSpec support. Additionally, I tried to make it interesting to a wider audience by really showcasing RSpec’s strengths, and trying to capture some of the red-green-refactor rhythm. NetBeans does work really well for this, but in my mind, the star of the show is RSpec.

I’m pleased with how it turned out considering I hadn’t done this sort of thing before. Special thanks to Cindy Church for putting it all together, including all the production: setup, recording, editing, even the music!

A QuickTime movie version is available as well. Check it out and let me know what you think.

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Why DTrace Makes Leopard a Must-Have Upgrade

Posted by Nick Sieger Tue, 05 Feb 2008 21:12:00 GMT

I feel like I’m actually a relative late-comer to Leopard, at least in my social circle. A lot of the folks in the Ruby community already had it installed the week after it was out, and were showing it off at RubyConf back in November. I just didn’t have a compelling reason to upgrade and disrupt my workflow at the time. Plus, mixed reports were coming out about data loss, UI nits, and other instabilities.

By the time I went out to purchase, 10.5.1 was already the version boxed in the stores, and in retrospect, it seemed worth the wait. I haven’t had a single complaint or major issue with the upgrade so far, and have been enjoying the noticeable zippiness of a freshly-installed system.

Time Machine has been a widely-publicized feature, and has been touted as one of the top reasons to upgrade. So I bought a small portable drive with some leftover holiday gift cards and set out to try it. Initially it seemed promising, except after a day or two of backups the process would stall out during the “preparing” stage. Eventually I noticed that the TM background process, backupd, was eating up 0.5GB of memory and up to 100% of one of the CPUs.

If I wasn’t a nerd making my living having my way with computers, I probably would have given up on Time Machine at this point, after a couple of hours scouring Google and the Apple discussion boards searching for similar problems. But I knew that backupd had to be doing something pathological, and I was compelled to find out what.

On Solaris systems, truss is usually the order of the day for problems like this. It literally vomits an endless listing of system calls invoked by a process into your terminal window. Except there’s no truss on OS X. Is there a replacement? Google mentioned ktrace, present on Tiger systems and earlier, but it’s gone in Leopard. Replaced by? DTrace.

Ahhh, DTrace! Another geeky Leopard-only feature. Certainly DTrace will be able to trace system calls in the same manner as truss. But being a complete DTrace newb, I had no idea where to start. So, like any lazy programmer does, I started shopping around for examples to get me started. Looking around, this article on MacTech looked promising, but didn’t have what I needed. Eventually, I ended up finding the DTrace Toolkit on the OpenSolaris site.

The DTrace Toolkit appears to be your one-stop shop for all things DTrace. If you need a kick-start reason to take a look at DTrace and get you going, this is it. In my case, lo and behold, one of the scripts included in the toolkit is called dtruss!

Many of the scripts in the toolkit are tailored towards a Solaris system, and dtruss is a prime example. It won’t quite work out of the box on Leopard, because a few of the system calls mentioned in the script are non-existent there. Changing the shebang line at the top of the script to #!/bin/bash, and repeatedly running it a few times with sudo ./dtruss -p <pid> will give you an idea of which ones; I simply commented these out until I was successfully able to trace a process.

Now, finally we can pop the stack back to my original problem with Time Machine and backupd. I launched a backup run and waited for the process to start consuming large amounts of CPU and memory. I located the PID of the process in Activity Monitor, and started tracing it with my modified dtruss script. And, sure enough, I saw the following output scrolling by endlessly in my terminal:

mmap(0x0, 0x5000, 0x3)     = 958464 0
getdirentriesattr(..., ..., ...)    = ....
munmap(0xEA000, 0x5000)    = 0 0
getxattr(..., ..., 0x0)     = -1 Err#93
getxattr(..., ..., 0x0)     = -1 Err#93
getxattr(..., ..., 0x0)     = -1 Err#93
getxattr(..., ..., 0x0)     = -1 Err#93
getxattr(..., ..., 0x0)     = -1 Err#93
getxattr(..., ..., 0x0)     = -1 Err#93
getxattr(..., ..., 0x0)     = -1 Err#93
getxattr(..., ..., 0x0)     = -1 Err#93
getxattr(..., ..., 0x0)     = -1 Err#93
getxattr(..., ..., 0x0)     = -1 Err#93
getxattr(..., ..., 0x0)     = -1 Err#93
getxattr(..., ..., 0x0)     = -1 Err#93
getxattr(..., ..., 0x0)     = -1 Err#93

(The ellipsis were actual memory addresses, I didn’t save the output.) What was interesting is that the same chunk of memory (the first argument to getxattr) was floating by repeatedly. Looking at the man page for getxattr, the signature is:

getxattr(const char *path, const char *name, void *value,
         size_t size, u_int32_t position, int options);

So, the first argument contains the path. Now, how can I get the contents of that memory address? The answer is inside dtruss. Closer to the top of the script is this DTrace code:

/* print 3 args, arg0 as a string */
/* not on leopard -- syscall::resolvepath:return */
    /* calculate elapsed time */
    this->elapsed = timestamp - self->start;
    self->start = 0;
    this->cpu = vtimestamp - self->vstart;
    self->vstart = 0;
    self->code = errno == 0 ? "" : "Err#";

    /* print optional fields */
    OPT_printid  ? printf("%6d/%d:  ", pid, tid) : 1;
    OPT_relative ? printf("%8d ", vtimestamp/1000) : 1;
    OPT_elapsed  ? printf("%7d ", this->elapsed/1000) : 1;
    OPT_cpu      ? printf("%6d ", this->cpu/1000) : 1;

    /* print main data */
    printf("%s(\"%S\", 0x%X, 0x%X)\t\t = %d %s%d\n", probefunc,
        copyinstr(self->arg0), self->arg1, self->arg2, (int)arg0,
        self->code, (int)errno);
    OPT_stack ? ustack()    : 1;
    OPT_stack ? trace("\n") : 1;
    self->arg0 = 0;
    self->arg1 = 0;
    self->arg2 = 0;

I only had to add syscall::getxattr:return to the list of matched probes, and now I could finally inspect the path argument to getxattr:

munmap(0xEA000, 0x5000)      = 0 0
@imap.gmail.com/[Gmail]/All Mail.imapmbox/Messages/1002680.emlx\0",
0x967288D4, 0x0)         = -1 Err#93
@imap.gmail.com/[Gmail]/All Mail.imapmbox/Messages/1002681.emlx\0",
0x967288D4, 0x0)         = -1 Err#93
@imap.gmail.com/[Gmail]/All Mail.imapmbox/Messages/1002682.emlx\0",
0x967288D4, 0x0)         = -1 Err#93
@imap.gmail.com/[Gmail]/All Mail.imapmbox/Messages/1002683.emlx\0",
0x967288D4, 0x0)         = -1 Err#93
@imap.gmail.com/[Gmail]/All Mail.imapmbox/Messages/1002684.emlx\0",
0x967288D4, 0x0)         = -1 Err#93
@imap.gmail.com/[Gmail]/All Mail.imapmbox/Messages/1002685.emlx\0",
0x967288D4, 0x0)         = -1 Err#93
@imap.gmail.com/[Gmail]/All Mail.imapmbox/Messages/1002686.emlx\0",
0x967288D4, 0x0)         = -1 Err#93
@imap.gmail.com/[Gmail]/All Mail.imapmbox/Messages/1002687.emlx\0",
0x967288D4, 0x0)         = -1 Err#93

D’oh! GMail! That directory has so many files, it took over two minutes just for ls to list all 487356 of them. Hundreds of thousands of email messages, all being re-inspected by Time Machine every time some new messages are added to the directory. I’ll leave it to someone else to point fingers at what the actual problem is here (a side-effect of TM’s usage of hard links? Mail.app inefficiently storing too many messages in a single directory?), but after all this I just decided that I didn’t want a backup of my GMail messages since they’re stored on the server. So I added the directory to the list of excluded directories in TM, wiped my backup, and started over. (TM had similar problems trying to complete an incremental backup with the existing backed-up copy of my mail on the backup disk, so I decided to wipe it and start fresh.) I won’t declare the problem completely solved yet, but if it happens again, I’ll just repeat this process to find the new culprit. Hopefully I don’t end up excluding my entire home directory!

This whole process was a revelation to me -- the fact that I could pinpoint the exact problem in a piece of system software despite having few notions of the internals of that software. The next time I have a nagging issue in Leopard, DTrace will be my tool of choice in tracking it down. Let’s just hope it’s not a problem with iTunes!

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