Adjust indexes on GitLab.com

Relates to https://gitlab.com/gitlab-org/gitlab/-/issues/296760

changelogs/unreleased/ab-index-rename.yml

+---
+title: Rename indexes to remove inconsistencies
+merge_request: 51011
+author:
+type: other

db/migrate/20210106191305_rename_indexes_on_git_lab_com.rb

+# frozen_string_literal: true
+
+# This migration aligns an existing database schema with what we actually expect
+# and fixes inconsistencies with index names and similar issues.
+#
+# This is intended for GitLab.com, but can be run on any instance.
+class RenameIndexesOnGitLabCom < ActiveRecord::Migration[6.0]
+  include Gitlab::Database::MigrationHelpers
+
+  DOWNTIME = false
+
+  disable_ddl_transaction!
+
+  def up
+    rename_index_if_exists :ldap_group_links, 'ldap_groups_pkey', 'ldap_group_links_pkey'
+
+    # Removes unique constraint, add unique index instead
+    replace_unique_constraint_with_index :emails, :email, 'emails_email_key', 'index_emails_on_email'
+    replace_unique_constraint_with_index :users, :confirmation_token, 'users_confirmation_token_key', 'index_users_on_confirmation_token'
+    replace_unique_constraint_with_index :users, :reset_password_token, 'users_reset_password_token_key', 'index_users_on_reset_password_token'
+    replace_unique_constraint_with_index :users, :email, 'users_email_key', 'index_users_on_email'
+
+    upgrade_to_primary_key(:schema_migrations, :version, 'schema_migrations_version_key', 'schema_migrations_pkey')
+  end
+
+  def down
+    # no-op
+  end
+
+  private
+
+  def replace_unique_constraint_with_index(table, columns, old_name, new_name)
+    return unless index_exists_by_name?(table, old_name)
+
+    add_concurrent_index table, columns, unique: true, name: new_name
+    execute "ALTER TABLE #{quote_table_name(table)} DROP CONSTRAINT #{quote_table_name(old_name)}"
+  end
+
+  def rename_index_if_exists(table, old_name, new_name)
+    return unless index_exists_by_name?(table, old_name)
+    return if index_exists_by_name?(table, new_name)
+
+    with_lock_retries do
+      rename_index table, old_name, new_name
+    end
+  end
+
+  def upgrade_to_primary_key(table, column, old_name, new_name)
+    return unless index_exists_by_name?(table, old_name)
+    return if index_exists_by_name?(table, new_name)
+
+    return if primary_key(table)
+
+    execute "ALTER TABLE #{quote_table_name(table)} ADD CONSTRAINT #{new_name} PRIMARY KEY (#{column})"
+    execute "ALTER TABLE #{quote_table_name(table)} DROP CONSTRAINT #{old_name}"
+  end
+end

db/schema_migrations/20210106191305

+938977d6379e484a53857304c339a024c32d8b71c2175574a72314e461d67e3b
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