[Bug 1713219] Re: 'apt-mark showauto' and 'apt show' is slow

[Julian Andres Klode]

There is no performance issue with the file format, the parsing is not
noticeable.

There is a massive design problem in the DepCache having to visit every
dependency in the cache and do marking stuff. This worked fine for tiny
sets, but scales superlinear to package count.

That's a very long time effort thing to fix for a future ABI break, we
need to only check those dependencies we actually care about.

Out of those 0.5s, probably about .4s are spent checking dependencies.
This will decrease by factor 10-50 presumably.

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Title:
  'apt-mark showauto' and 'apt show' is slow

Status in apt package in Ubuntu:
  Triaged

Bug description:
  $ time apt-mark showauto >/dev/null

  real	0m0.587s
  user	0m0.552s
  sys	0m0.016s

  When I run the command first time, it is even much slower.

  I could do the job in fraction of a time using awk in POSIX shell
  script:

  auto_file='/var/lib/apt/extended_states'
  eval $(apt-config shell auto_file Dir::State::extended_states/f)
  awk '/^Package:/ {
  	pkg=$2
  	getline; arch=$2
  	getline
  	if($2==1) print pkg ":" arch
  }' "$auto_file" | CL_ALL=C sort -u

  real	0m0.019s
  user	0m0.008s
  sys	0m0.000s

  That prints architecture for every package and shows entries in
  slightly different order, though. And the file could be out of date
  showing packages that are not installed?!?

  Similarly

  apt show <pkg>

  is slow. (It also shows whether a package is manually or automatically
  installed.

  ProblemType: Bug
  DistroRelease: Ubuntu 14.04
  Package: apt 1.0.1ubuntu2.17
  ProcVersionSignature: Ubuntu 4.4.0-92.115~14.04.1-generic 4.4.76
  Uname: Linux 4.4.0-92-generic x86_64
  ApportVersion: 2.14.1-0ubuntu3.25
  Architecture: amd64
  CurrentDesktop: XFCE
  Date: Sat Aug 26 12:59:00 2017
  EcryptfsInUse: Yes
  InstallationDate: Installed on 2014-09-21 (1070 days ago)
  InstallationMedia: Ubuntu-Studio 14.04.1 LTS "Trusty Tahr" - Release amd64 (20140722.1)
  SourcePackage: apt
  UpgradeStatus: No upgrade log present (probably fresh install)
  modified.conffile..etc.cron.daily.apt: [modified]
  modified.conffile..etc.kernel.postinst.d.apt.auto.removal: [modified]
  mtime.conffile..etc.cron.daily.apt: 2017-05-03T10:27:27.617839
  mtime.conffile..etc.kernel.postinst.d.apt.auto.removal: 2017-06-01T14:39:39.236080

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