Drop unused mirror_data index

changelogs/unreleased/326009-remove-unused-index.yml

+---
+title: Drop unused mirror_data index
+merge_request: 58349
+author:
+type: performance

db/migrate/20210401134455_remove_index_mirror_data_on_next_execution_and_retry_count.rb

+# frozen_string_literal: true
+
+# See https://docs.gitlab.com/ee/development/migration_style_guide.html
+# for more information on how to write migrations for GitLab.
+
+class RemoveIndexMirrorDataOnNextExecutionAndRetryCount < ActiveRecord::Migration[6.0]
+  include Gitlab::Database::MigrationHelpers
+
+  disable_ddl_transaction!
+
+  DOWNTIME = false
+
+  INDEX_NAME = 'index_mirror_data_on_next_execution_and_retry_count'
+
+  def up
+    remove_concurrent_index(
+      :project_mirror_data,
+      %i[next_execution_timestamp retry_count],
+      name: INDEX_NAME
+    )
+  end
+
+  def down
+    add_concurrent_index(
+      :project_mirror_data,
+      %i[next_execution_timestamp retry_count],
+      name: INDEX_NAME
+    )
+  end
+end

db/schema_migrations/20210401134455

+3420d83bf8a1f44e69960849efa25525883f17a2776ae3ce28db855cd550ca8e
\ No newline at end of file

db/structure.sql

@@ -23140,8 +23140,6 @@ CREATE INDEX index_milestones_on_title_trigram ON milestones USING gin (title gi
 
 CREATE INDEX index_mirror_data_non_scheduled_or_started ON project_mirror_data USING btree (next_execution_timestamp, retry_count) WHERE ((status)::text <> ALL ('{scheduled,started}'::text[]));
 
-CREATE INDEX index_mirror_data_on_next_execution_and_retry_count ON project_mirror_data USING btree (next_execution_timestamp, retry_count);
-
 CREATE UNIQUE INDEX index_mr_blocks_on_blocking_and_blocked_mr_ids ON merge_request_blocks USING btree (blocking_merge_request_id, blocked_merge_request_id);
 
 CREATE INDEX index_mr_cleanup_schedules_timestamps ON merge_request_cleanup_schedules USING btree (scheduled_at) WHERE (completed_at IS NULL);