[Bug 1874272] Re: Stage "searching for obsolete software" takes a very long time (30 minutes)

[Gregory P Smith]

Judging by the 100% cpu utilization and entries in /var/log/dist-
upgrade/apt.log... as an outside observer black box guess: is this thing
loading the parsing the entire package dependency graph repeatedly once
per potential package?

88% complete after 30 minutes of CPU time...

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https://bugs.launchpad.net/bugs/1874272

Title:
  Stage "searching for obsolete software" takes a very long time (30
  minutes)

Status in ubuntu-release-upgrader package in Ubuntu:
  Confirmed
Status in ubuntu-release-upgrader source package in Focal:
  Confirmed

Bug description:
  Test Case:
  1. Fresh Bionic installation from 18.04.4 + all updates applied
  2. Run: update-manager -d
  3. Proceed with the upgrade.

  Actual Result:
  Everything goes well but the stage "Searching for obsolete software" takes a very long time.

  ProblemType: Bug
  DistroRelease: Ubuntu 20.04
  Package: ubuntu-release-upgrader-core 1:20.04.18
  ProcVersionSignature: Ubuntu 5.4.0-26.30-generic 5.4.30
  Uname: Linux 5.4.0-26-generic x86_64
  ApportVersion: 2.20.11-0ubuntu27
  Architecture: amd64
  CasperMD5CheckResult: skip
  CrashDB: ubuntu
  CurrentDesktop: ubuntu:GNOME
  Date: Wed Apr 22 10:34:19 2020
  InstallationDate: Installed on 2020-04-20 (2 days ago)
  InstallationMedia: Ubuntu 18.04.4 LTS "Bionic Beaver" - Release amd64 (20200203.1)
  PackageArchitecture: all
  ProcEnviron:
   TERM=xterm-256color
   PATH=(custom, no user)
   XDG_RUNTIME_DIR=<set>
   LANG=en_US.UTF-8
   SHELL=/bin/bash
  SourcePackage: ubuntu-release-upgrader
  Symptom: ubuntu-release-upgrader
  UpgradeStatus: Upgraded to focal on 2020-04-22 (0 days ago)
  VarLogDistupgradeTermlog:

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