Remove TMP index for emails table

changelogs/unreleased/remove-tmp-emails-index.yml

+---
+title: Remove tmp_index_for_email_unconfirmation_migration index in the emails table
+merge_request: 50981
+author:
+type: other

db/migrate/20210106153021_drop_tmp_index_on_emails.rb

+# frozen_string_literal: true
+
+class DropTmpIndexOnEmails < ActiveRecord::Migration[6.0]
+  include Gitlab::Database::MigrationHelpers
+
+  DOWNTIME = false
+  EMAIL_INDEX_NAME = 'tmp_index_for_email_unconfirmation_migration'
+
+  disable_ddl_transaction!
+
+  def up
+    Gitlab::BackgroundMigration.steal('WrongfullyConfirmedEmailUnconfirmer')
+
+    remove_concurrent_index_by_name(:emails, EMAIL_INDEX_NAME)
+  end
+
+  def down
+    add_concurrent_index(:emails, :id, where: 'confirmed_at IS NOT NULL', name: EMAIL_INDEX_NAME)
+  end
+end

db/schema_migrations/20210106153021

+71e005116082a59e40194fe5f9a500e31d67a011500d12aeecd59cb64d611848
\ No newline at end of file

db/structure.sql

@@ -23105,8 +23105,6 @@ CREATE INDEX temporary_index_vulnerabilities_on_id ON vulnerabilities USING btre
 
 CREATE UNIQUE INDEX term_agreements_unique_index ON term_agreements USING btree (user_id, term_id);
 
-CREATE INDEX tmp_index_for_email_unconfirmation_migration ON emails USING btree (id) WHERE (confirmed_at IS NOT NULL);
-
 CREATE INDEX tmp_index_on_vulnerabilities_non_dismissed ON vulnerabilities USING btree (id) WHERE (state <> 2);
 
 CREATE UNIQUE INDEX unique_merge_request_metrics_by_merge_request_id ON merge_request_metrics USING btree (merge_request_id);