Cleanup: Make MONITOR_LSN_CHECKPOINT_AGE a value.

Compute MONITOR_LSN_CHECKPOINT_AGE on demand in
srv_mon_process_existing_counter().
This allows us to remove the overhead of MONITOR_SET
calls for the counter.

mysql-test/suite/innodb/r/innodb_skip_innodb_is_tables.result

@@ -198,7 +198,7 @@ log_checkpoints	recovery	0	NULL	NULL	NULL	0	NULL	NULL	NULL	NULL	NULL	NULL	NULL	0
 log_lsn_last_flush	recovery	0	NULL	NULL	NULL	0	NULL	NULL	NULL	NULL	NULL	NULL	NULL	0	value	LSN of Last flush
 log_lsn_last_checkpoint	recovery	0	NULL	NULL	NULL	0	NULL	NULL	NULL	NULL	NULL	NULL	NULL	0	value	LSN at last checkpoint
 log_lsn_current	recovery	0	NULL	NULL	NULL	0	NULL	NULL	NULL	NULL	NULL	NULL	NULL	0	value	Current LSN value
-log_lsn_checkpoint_age	recovery	0	NULL	NULL	NULL	0	NULL	NULL	NULL	NULL	NULL	NULL	NULL	0	counter	Current LSN value minus LSN at last checkpoint
+log_lsn_checkpoint_age	recovery	0	NULL	NULL	NULL	0	NULL	NULL	NULL	NULL	NULL	NULL	NULL	0	value	Current LSN value minus LSN at last checkpoint
 log_lsn_buf_pool_oldest	recovery	0	NULL	NULL	NULL	0	NULL	NULL	NULL	NULL	NULL	NULL	NULL	0	value	The oldest modified block LSN in the buffer pool
 log_max_modified_age_async	recovery	0	NULL	NULL	NULL	0	NULL	NULL	NULL	NULL	NULL	NULL	NULL	0	value	Maximum LSN difference; when exceeded, start asynchronous preflush
 log_max_modified_age_sync	recovery	0	NULL	NULL	NULL	0	NULL	NULL	NULL	NULL	NULL	NULL	NULL	0	value	Maximum LSN difference; when exceeded, start synchronous preflush

storage/innobase/include/log0log.ic

@@ -312,9 +312,6 @@ log_reserve_and_write_fast(
 
 	log_sys.lsn += len;
 
-	MONITOR_SET(MONITOR_LSN_CHECKPOINT_AGE,
-		    log_sys.lsn - log_sys.last_checkpoint_lsn);
-
 	return(log_sys.lsn);
 }
 

storage/innobase/log/log0log.cc

@@ -554,8 +554,6 @@ void log_t::create()
   buf_free= LOG_BLOCK_HDR_SIZE;
   lsn= LOG_START_LSN + LOG_BLOCK_HDR_SIZE;
 
-  MONITOR_SET(MONITOR_LSN_CHECKPOINT_AGE, lsn - last_checkpoint_lsn);
-
   log_scrub_thread_active= !srv_read_only_mode && srv_scrub_log;
   if (log_scrub_thread_active) {
     log_scrub_event= os_event_create("log_scrub_event");
@@ -1405,8 +1403,6 @@ void log_write_checkpoint_info(lsn_t end_lsn)
 	log_sys.next_checkpoint_no++;
 
 	log_sys.last_checkpoint_lsn = log_sys.next_checkpoint_lsn;
-	MONITOR_SET(MONITOR_LSN_CHECKPOINT_AGE,
-		    log_sys.lsn - log_sys.last_checkpoint_lsn);
 
 	DBUG_PRINT("ib_log", ("checkpoint ended at " LSN_PF
 			      ", flushed to " LSN_PF,

storage/innobase/log/log0recv.cc

@@ -3553,9 +3553,6 @@ recv_recovery_from_checkpoint_start(lsn_t flush_lsn)
 		fil_names_clear(log_sys.last_checkpoint_lsn, true);
 	}
 
-	MONITOR_SET(MONITOR_LSN_CHECKPOINT_AGE,
-		    log_sys.lsn - log_sys.last_checkpoint_lsn);
-
 	log_sys.next_checkpoint_no = ++checkpoint_no;
 
 	mutex_enter(&recv_sys.mutex);

storage/innobase/srv/srv0mon.cc

@@ -889,7 +889,8 @@ static monitor_info_t	innodb_counter_info[] =
 
 	{"log_lsn_checkpoint_age", "recovery",
 	 "Current LSN value minus LSN at last checkpoint",
-	 MONITOR_NONE,
+	 static_cast<monitor_type_t>(
+	 MONITOR_EXISTING | MONITOR_DISPLAY_CURRENT),
 	 MONITOR_DEFAULT_START, MONITOR_LSN_CHECKPOINT_AGE},
 
 	{"log_lsn_buf_pool_oldest", "recovery",
@@ -1993,6 +1994,13 @@ srv_mon_process_existing_counter(
 		mutex_exit(&log_sys.mutex);
 		break;
 
+	case MONITOR_LSN_CHECKPOINT_AGE:
+		mutex_enter(&log_sys.mutex);
+		value = static_cast<mon_type_t>(log_sys.lsn
+						- log_sys.last_checkpoint_lsn);
+		mutex_exit(&log_sys.mutex);
+		break;
+
 	case MONITOR_OVLD_BUF_OLDEST_LSN:
 		value = (mon_type_t) buf_pool_get_oldest_modification();
 		break;

storage/innobase/srv/srv0start.cc

@@ -341,8 +341,6 @@ static dberr_t create_log_file(lsn_t lsn, std::string& logfile0)
 	log_sys.buf_free = LOG_BLOCK_HDR_SIZE;
 	log_sys.lsn += LOG_BLOCK_HDR_SIZE;
 
-	MONITOR_SET(MONITOR_LSN_CHECKPOINT_AGE,
-		    (log_sys.lsn - log_sys.last_checkpoint_lsn));
 	log_mutex_exit();
 
 	log_make_checkpoint();

storage/rocksdb/mysql-test/rocksdb/r/innodb_i_s_tables_disabled.result

@@ -180,7 +180,7 @@ log_checkpoints	recovery	0	NULL	NULL	NULL	0	NULL	NULL	NULL	NULL	NULL	NULL	NULL	0
 log_lsn_last_flush	recovery	0	NULL	NULL	NULL	0	NULL	NULL	NULL	NULL	NULL	NULL	NULL	0	value	LSN of Last flush
 log_lsn_last_checkpoint	recovery	0	NULL	NULL	NULL	0	NULL	NULL	NULL	NULL	NULL	NULL	NULL	0	value	LSN at last checkpoint
 log_lsn_current	recovery	0	NULL	NULL	NULL	0	NULL	NULL	NULL	NULL	NULL	NULL	NULL	0	value	Current LSN value
-log_lsn_checkpoint_age	recovery	0	NULL	NULL	NULL	0	NULL	NULL	NULL	NULL	NULL	NULL	NULL	0	counter	Current LSN value minus LSN at last checkpoint
+log_lsn_checkpoint_age	recovery	0	NULL	NULL	NULL	0	NULL	NULL	NULL	NULL	NULL	NULL	NULL	0	value	Current LSN value minus LSN at last checkpoint
 log_lsn_buf_pool_oldest	recovery	0	NULL	NULL	NULL	0	NULL	NULL	NULL	NULL	NULL	NULL	NULL	0	value	The oldest modified block LSN in the buffer pool
 log_max_modified_age_async	recovery	0	NULL	NULL	NULL	0	NULL	NULL	NULL	NULL	NULL	NULL	NULL	0	value	Maximum LSN difference; when exceeded, start asynchronous preflush
 log_max_modified_age_sync	recovery	0	NULL	NULL	NULL	0	NULL	NULL	NULL	NULL	NULL	NULL	NULL	0	value	Maximum LSN difference; when exceeded, start synchronous preflush