Add index for selecting active agent tokens

Changelog: added

db/post_migrate/20220111023852_index_cluster_agent_tokens_on_status.rb

+# frozen_string_literal: true
+
+class IndexClusterAgentTokensOnStatus < Gitlab::Database::Migration[1.0]
+  disable_ddl_transaction!
+
+  INDEX_NAME = 'index_cluster_agent_tokens_on_agent_id_status_last_used_at'
+
+  def up
+    add_concurrent_index :cluster_agent_tokens, 'agent_id, status, last_used_at DESC NULLS LAST', name: INDEX_NAME
+  end
+
+  def down
+    remove_concurrent_index_by_name :cluster_agent_tokens, INDEX_NAME
+  end
+end

db/schema_migrations/20220111023852

+fdb6e193748f9933aa3ae60fab41960e06d4edf271048fc5f6c9c465d30a8334
\ No newline at end of file

db/structure.sql

@@ -25667,6 +25667,8 @@ CREATE UNIQUE INDEX index_ci_variables_on_project_id_and_key_and_environment_sco
 
 CREATE INDEX index_cluster_agent_tokens_on_agent_id_and_last_used_at ON cluster_agent_tokens USING btree (agent_id, last_used_at DESC NULLS LAST);
 
+CREATE INDEX index_cluster_agent_tokens_on_agent_id_status_last_used_at ON cluster_agent_tokens USING btree (agent_id, status, last_used_at DESC NULLS LAST);
+
 CREATE INDEX index_cluster_agent_tokens_on_created_by_user_id ON cluster_agent_tokens USING btree (created_by_user_id);
 
 CREATE UNIQUE INDEX index_cluster_agent_tokens_on_token_encrypted ON cluster_agent_tokens USING btree (token_encrypted);