[Bug 1916935] Re: Major changes in sorting method upgrade 18.04->18.04.5 due to base-files change

[Balint Reczey]

@paelzer Thank you for the triaging and the detailed explanation. Since this change slipped in too long ago I don't think it should be reverted.
I think Postresql could check if there was a change in sorting compared to the which the indices were created with, but this installation does not uses Postgresql from the archive so that would just be an unrelated improvement. Maybe Postgres already does that.

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Title:
  Major changes in sorting method upgrade 18.04->18.04.5 due to base-
  files change

Status in base-files package in Ubuntu:
  New
Status in glibc package in Ubuntu:
  Invalid
Status in postgresql-10 package in Ubuntu:
  Invalid
Status in base-files source package in Bionic:
  New

Bug description:
  I had an Ubuntu 18.04.0 with Postgres 9.6.

  Before Ubuntu upgrade following command result was:

  [code]
  vodka at ubuntu140:~$  ( echo "1-1"; echo "11" ) | LC_COLLATE=en_US.UTF-8 sort
  1-1
  11
  [/code]

  But after upgrading Ubuntu 18.04 to latest release via apt upgrade
  (18.04.5) result of the command above totally changed:

  [code]
  vodka at ubuntu140:~$ ( echo "1-1"; echo "11" ) | LC_COLLATE=en_US.UTF-8 sort
  11
  1-1
  [/code]

  Due to this our production Postgres database started work very slowly
  and we had a long downtime for REINDEX. Sorting method is very
  important for Postgres database:
  https://wiki.postgresql.org/wiki/Locale_data_changes

  Please, read "Testing collation" part.

  Is it normal behavior for Ubuntu? Why glibc totally changed within LTS
  release without 'major upgrade'? I did not expect this...

  ProblemType: Bug
  DistroRelease: Ubuntu 18.04
  Package: libc-bin 2.27-3ubuntu1.4
  ProcVersionSignature: Ubuntu 4.15.0-136.140-generic 4.15.18
  Uname: Linux 4.15.0-136-generic x86_64
  ApportVersion: 2.20.9-0ubuntu7.23
  Architecture: amd64
  Date: Thu Feb 25 13:13:03 2021
  Dependencies:
   gcc-8-base 8.4.0-1ubuntu1~18.04
   libc6 2.27-3ubuntu1.4
   libgcc1 1:8.4.0-1ubuntu1~18.04
  InstallationDate: Installed on 2021-02-25 (0 days ago)
  InstallationMedia: Ubuntu-Server 18.04 LTS "Bionic Beaver" - Release amd64 (20180426)
  SourcePackage: glibc
  UpgradeStatus: No upgrade log present (probably fresh install)

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