Remove unnecessary index on services for usage data

- index_services_on_type_id_when_active_not_instance_not_template was
  added https://gitlab.com/gitlab-org/gitlab/-/merge_requests/27093 and
  updated https://gitlab.com/gitlab-org/gitlab/-/merge_requests/38147
  just for the usage data.
- There is no other query for template = FALSE in the codebase.
- We will maintain the partial index for (type, id).

changelogs/unreleased/268248-remove-index-service-for-usage-data.yml

+---
+title: Remove unnecessary index on services for usage data
+merge_request: 45655
+author:
+type: other

db/post_migrate/20201020102551_remove_index_service_for_usage_data.rb

+# frozen_string_literal: true
+
+class RemoveIndexServiceForUsageData < ActiveRecord::Migration[6.0]
+  include Gitlab::Database::MigrationHelpers
+
+  DOWNTIME = false
+  INDEX_NAME = 'index_services_on_type_id_when_active_not_instance_not_template'
+
+  disable_ddl_transaction!
+
+  def up
+    remove_concurrent_index_by_name :services, INDEX_NAME
+  end
+
+  def down
+    add_concurrent_index :services, [:type, :id], where: 'active = TRUE AND instance = FALSE AND template = FALSE', name: INDEX_NAME
+  end
+end

db/schema_migrations/20201020102551

+ba16ad5a51494f436dc47ffb924f94ce7795bfd3b9061ca58d1c8dda238245e9
\ No newline at end of file

db/structure.sql

@@ -21536,8 +21536,6 @@ CREATE UNIQUE INDEX index_services_on_type_and_template_partial ON services USIN
 
 CREATE INDEX index_services_on_type_id_when_active_and_project_id_not_null ON services USING btree (type, id) WHERE ((active = true) AND (project_id IS NOT NULL));
 
-CREATE INDEX index_services_on_type_id_when_active_not_instance_not_template ON services USING btree (type, id) WHERE ((active = true) AND (instance = false) AND (template = false));
-
 CREATE UNIQUE INDEX index_services_on_unique_group_id_and_type ON services USING btree (group_id, type);
 
 CREATE UNIQUE INDEX index_shards_on_name ON shards USING btree (name);