[Bug 598282] Re: command-not-found slow for its task

[rgrig]

On Fri, Jul 22, 2011 at 3:03 AM, Zygmunt Krynicki
<zygmunt.krynicki at canonical.com> wrote:
> While I appreciate your enthusiasm and desire to fix this I have a few

Actually, I don't have much of either. But thanks for your appreciation.
:)

> 1) Unless I missed something your implementation always reads the
whole database file, I would rather avoid that.

That's actually what makes it fast, so you should not avoid it. With
non-SSD one seek takes roughly the same amount of time as reading
sequentially a few MB; with SSD, it's fast anyway. GDBM has to
optimize behind the scenes to also read and cache the whole thing. (If
it doesn't, then that's what is slow.)

> 2) The similar result search you employed is much weaker than the one
used by current implementation, you do not look for any permutations of
the input string, just for substrings.

Look again.

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https://bugs.launchpad.net/bugs/598282

Title:
  command-not-found slow for its task

Status in “command-not-found” package in Ubuntu:
  Confirmed

Bug description:
  Binary package hint: command-not-found

  Considering command-not-found has a relatively simple job. It seems
  that it is horribly over-engineered for its task. And as such, we have
  runtimes such as this:

  
  $ time sl
  The program 'sl' is currently not installed.  You can install it by typing:
  sudo apt-get install sl

  real	0m1.715s
  user	0m0.680s
  sys	0m0.228s

  
  $ time sl
  The program 'sl' is currently not installed.  You can install it by typing:
  sudo apt-get install sl

  real	0m0.759s
  user	0m0.592s
  sys	0m0.116s


  
  A little over a year ago I wrote a replacement script, that I've numerously lost, found, updated and forgotten about. It is about 250 LOC, and kept with one thing in mind, KISS. What surprises me most though is not the simplicity in comparison, but that it is 14x faster at executing it's job.
  That script can be found here: http://ubuntuforums.org/showpost.php?p=7116396&postcount=1
  And this is how well it runs in comparison.

  
  $ time sl
  The program 'sl' is currently not installed.  You can install it by typing:
  sudo apt-get install sl

  real	0m0.079s
  user	0m0.036s
  sys	0m0.016s

  
  $ time sl
  The program 'sl' is currently not installed.  You can install it by typing:
  sudo apt-get install sl

  real	0m0.062s
  user	0m0.044s
  sys	0m0.016s

  
  You would be forgiven in thinking I used a compiled application to get such low times, but it is not, I tell you that now.

  So the ultimate question is, why punish users? I think some act needs
  to be gotten together to clamp down on the speed demons in this
  application. As IMO, it is in an unacceptable state.

  Regards

  ProblemType: Bug
  DistroRelease: Ubuntu 10.04
  Package: command-not-found 0.2.40ubuntu5
  ProcVersionSignature: Ubuntu 2.6.32-22.36-generic 2.6.32.11+drm33.2
  Uname: Linux 2.6.32-22-generic i686
  Architecture: i386
  Date: Thu Jun 24 22:33:33 2010
  PackageArchitecture: all
  ProcEnviron:
   LANG=en_GB.utf8
   SHELL=/bin/bash
  SourcePackage: command-not-found

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