Adjust indexes for iterations and iteration cadences

Adding an index for fetching iteration cadences that require
iterations in advance to be generated

Iteration title does not need to be unique per group anymore
keeping uniqueness per cadence should be enough.

Changelog: added

db/migrate/20210527065005_add_index_for_cadence_iterations_automation.rb

+# frozen_string_literal: true
+
+class AddIndexForCadenceIterationsAutomation < ActiveRecord::Migration[6.0]
+  include Gitlab::Database::MigrationHelpers
+
+  INDEX_NAME = 'cadence_create_iterations_automation'
+
+  disable_ddl_transaction!
+
+  def up
+    return if index_exists_by_name?(:iterations_cadences, INDEX_NAME)
+
+    execute(
+      <<-SQL
+        CREATE INDEX CONCURRENTLY #{INDEX_NAME} ON iterations_cadences
+        USING BTREE(automatic, duration_in_weeks, (DATE ((COALESCE("iterations_cadences"."last_run_date", DATE('01-01-1970')) + "iterations_cadences"."duration_in_weeks" * INTERVAL '1 week')))) 
+        WHERE duration_in_weeks IS NOT NULL
+      SQL
+    )
+  end
+
+  def down
+    remove_concurrent_index_by_name :iterations_cadences, INDEX_NAME
+  end
+end

db/migrate/20210529164247_change_iterations_title_uniqueness_index.rb

+# frozen_string_literal: true
+
+class ChangeIterationsTitleUniquenessIndex < ActiveRecord::Migration[6.0]
+  include Gitlab::Database::MigrationHelpers
+
+  INDEX_NAME = 'index_sprints_on_iterations_cadence_id_and_title'
+  OLD_INDEX_NAME = 'index_sprints_on_group_id_and_title'
+
+  disable_ddl_transaction!
+
+  def up
+    add_concurrent_index :sprints, [:iterations_cadence_id, :title], name: INDEX_NAME, unique: true
+    remove_concurrent_index_by_name :sprints, OLD_INDEX_NAME
+  end
+
+  def down
+    # noop
+    # rollback would not work as we can have duplicate records once the unique `index_sprints_on_group_id_and_title` index is removed
+  end
+end

db/schema_migrations/20210527065005

+983b736defaa128f7466a784d2a06de293fa6b1cee76121e533e7966d19aad73
\ No newline at end of file

db/schema_migrations/20210529164247

+8aa9e00be5f2bc6076f4a42a479aff4318b9e4d3da48798117fec67df7158db4
\ No newline at end of file

db/structure.sql

@@ -22305,6 +22305,8 @@ CREATE INDEX approval_mr_rule_index_merge_request_id ON approval_merge_request_r
 
 CREATE UNIQUE INDEX bulk_import_trackers_uniq_relation_by_entity ON bulk_import_trackers USING btree (bulk_import_entity_id, relation);
 
+CREATE INDEX cadence_create_iterations_automation ON iterations_cadences USING btree (automatic, duration_in_weeks, date((COALESCE(last_run_date, '1970-01-01'::date) + ((duration_in_weeks)::double precision * '7 days'::interval)))) WHERE (duration_in_weeks IS NOT NULL);
+
 CREATE INDEX ci_builds_gitlab_monitor_metrics ON ci_builds USING btree (status, created_at, project_id) WHERE ((type)::text = 'Ci::Build'::text);
 
 CREATE INDEX code_owner_approval_required ON protected_branches USING btree (project_id, code_owner_approval_required) WHERE (code_owner_approval_required = true);
@@ -24647,7 +24649,7 @@ CREATE INDEX index_sprints_on_due_date ON sprints USING btree (due_date);
 
 CREATE INDEX index_sprints_on_group_id ON sprints USING btree (group_id);
 
-CREATE UNIQUE INDEX index_sprints_on_group_id_and_title ON sprints USING btree (group_id, title) WHERE (group_id IS NOT NULL);
+CREATE UNIQUE INDEX index_sprints_on_iterations_cadence_id_and_title ON sprints USING btree (iterations_cadence_id, title);
 
 CREATE UNIQUE INDEX index_sprints_on_project_id_and_iid ON sprints USING btree (project_id, iid);