Improve migration for Multipple issue assignee feature

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Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• API support added
• Tests
  • Added for this feature/bug
  • All builds are passing
• Conform by the merge request performance guides
• Conform by the style guides
• Branch has no merge conflicts with master (if it does - rebase it please)
• Squashed related commits together

What are the relevant issue numbers?

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• df8c545c - Improve migration for Multipple issue assignee feature

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unmarked as a Work In Progress

mentioned in issue gitlab-com/infrastructure#1803 (closed)

@yorickpeterse We're creating table with create table AS which basically does not let us to adjust the schema

OK, we can alter the table in a post-migration

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• 7ec034b2 - Improve migration for Multipple issue assignee feature

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• 7ec034b2...43befaf2 - 16 commits from branch master
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resolved all discussions

mentioned in merge request !11406 (closed)

@vsizov I can't quite make it out based on the migration names, but are we 100% the order is still correct with some of them having been renamed? Other than that I have some picky comments, but nothing too serious.

added ~874211 ~149423 database labels

changed milestone to %9.2

@selfup @timothyandrew Just in case you're not aware of this (I think the two of you are), but once this MR is merged this should be picked into the RC and released.

@yorickpeterse I have not renamed any migration, this is how the diff is shown.

mentioned in issue #32372 (closed)

resolved all discussions

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approved this merge request

marked the checklist item Changelog entry added, if necessary as completed

marked the checklist item Documentation created/updated as completed

marked the checklist item API support added as completed

marked the checklist item API support added as incomplete

marked the checklist item Conform by the merge request performance guides as completed

marked the checklist item Conform by the style guides as completed

marked the checklist item Branch has no merge conflicts with master (if it does - rebase it please) as completed

marked the checklist item Squashed related commits together as completed

Rollback for MySQL is broken

Mysql2::Error: Error on rename of './gitlabhq_development/#sql-ac69_26' to './gitlabhq_development/issue_assignees' (errno: 150 - Foreign key constraint is incorrectly formed): DROP INDEX `index_issue_assignees_on_issue_id_and_user_id` ON `issue_assignees`/Users/valery/.rvm/gems/ruby-2.3.3/gems/activerecord-4.2.8/lib/active_record/connection_adapters/abstract_mysql_adapter.rb:309:in `query'

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• 793b9a5c - Improve migration for Multipple issue assignee feature

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OK, it's ready to go.

approved this merge request

enabled an automatic merge when the pipeline for 793b9a5c succeeds

merged

mentioned in commit c7a7fc17

mentioned in commit 5e69a4b9

Picked into 9-2-stable, will go into 9.2.0-rc3.

This was picked a while ago. Sorry for the late update :P