Update issue indexes on relative position

Changes the existing index to use the correct ID order and removes a
redundant index

db/post_migrate/20210927153807_update_issues_relative_position_indexes.rb

+# frozen_string_literal: true
+
+class UpdateIssuesRelativePositionIndexes < Gitlab::Database::Migration[1.0]
+  disable_ddl_transaction!
+
+  RELATIVE_POSITION_INDEX_NAME = 'idx_issues_on_project_id_and_rel_asc_and_id'
+  RELATIVE_POSITION_STATE_INDEX_NAME = 'idx_issues_on_project_id_and_rel_position_and_state_id_and_id'
+
+  NEW_RELATIVE_POSITION_STATE_INDEX_NAME = 'idx_issues_on_project_id_and_rel_position_and_id_and_state_id'
+
+  def up
+    add_concurrent_index :issues, [:project_id, :relative_position, :id, :state_id], name: NEW_RELATIVE_POSITION_STATE_INDEX_NAME
+
+    remove_concurrent_index_by_name :issues, RELATIVE_POSITION_INDEX_NAME
+    remove_concurrent_index_by_name :issues, RELATIVE_POSITION_STATE_INDEX_NAME
+  end
+
+  def down
+    add_concurrent_index :issues, [:project_id, :relative_position, :state_id, :id], order: { id: :desc }, name: RELATIVE_POSITION_STATE_INDEX_NAME
+    add_concurrent_index :issues, [:project_id, :relative_position, :id], name: RELATIVE_POSITION_INDEX_NAME
+
+    remove_concurrent_index_by_name :issues, NEW_RELATIVE_POSITION_STATE_INDEX_NAME
+  end
+end

db/schema_migrations/20210927153807

+8e54f43a955023e422bf40476f468fbdf04f06e806b08fddf35208c65607fec3
\ No newline at end of file

db/structure.sql

@@ -24038,9 +24038,7 @@ CREATE INDEX idx_issues_on_project_id_and_created_at_and_id_and_state_id ON issu
 
 CREATE INDEX idx_issues_on_project_id_and_due_date_and_id_and_state_id ON issues USING btree (project_id, due_date, id, state_id) WHERE (due_date IS NOT NULL);
 
-CREATE INDEX idx_issues_on_project_id_and_rel_asc_and_id ON issues USING btree (project_id, relative_position, id);
-
-CREATE INDEX idx_issues_on_project_id_and_rel_position_and_state_id_and_id ON issues USING btree (project_id, relative_position, state_id, id DESC);
+CREATE INDEX idx_issues_on_project_id_and_rel_position_and_id_and_state_id ON issues USING btree (project_id, relative_position, id, state_id);
 
 CREATE INDEX idx_issues_on_project_id_and_updated_at_and_id_and_state_id ON issues USING btree (project_id, updated_at, id, state_id);