在Oracle中有一个事件叫Heartbeat，这个词在很多地方被提及，并且有着不同的含义(比如RAC中)，我们这里要讨论的是CKPT的Heartbeat机制。
Oracle通过CKPT进程每3秒将Heartbeat写入控制文件，以减少故障时的恢复时间(这个我们后面再详细阐述)。
我们可以通过如下方法验证这个过程。
1.首先在系统级启用10046时间跟踪
并重新启动数据库使之生效
[oracle@jumper oracle]$ sqlplus "/ as sysdba"SQL*Plus: Release 9.2.0.4.0 - Production on Thu Jan 19 09:24:04 2006Copyright (c) 1982, 2002, Oracle Corporation. All rights reserved.Connected to:Oracle9i Enterprise Edition Release 9.2.0.4.0 - ProductionWith the Partitioning optionJServer Release 9.2.0.4.0 - Production
SQL> alter system set event='10046 trace name context forever,level 12' scope=spfile;System altered.
SQL> shutdown immediate;Database closed.Database dismounted.ORACLE instance shut down.SQL> startup
ORACLE instance started.
Total System Global Area 114365800 bytesFixed Size
451944 bytesVariable Size
50331648 bytesDatabase Buffers
62914560 bytesRedo Buffers
667648 bytesDatabase mounted.
Database opened.
SQL> exit
Disconnected from Oracle9i Enterprise Edition Release 9.2.0.4.0 - ProductionWith the Partitioning optionJServer Release 9.2.0.4.0 - Production
2.检查bdump目录下生成的跟踪文件
目录在$ORACLE_HOME/admin/$ORACLE_SID/bdump目录下，每个后台进程都会生成一个跟踪文件。
[oracle@jumper bdump]$ ls
20050424_alert_conner.log conner_arc0_2569.trc conner_dbw0_2559.trc conner_reco_2567.trcalert_conner.log conner_arc1_2571.trc conner_lgwr_2561.trc conner_smon_2565.trca.sql conner_ckpt_2563.trc conner_pmon_2557.trc
3.检查CKPT进程的跟踪文件
我们可以很容易的发现CKPT进程每3秒都对控制文件进行一次写入
[oracle@jumper bdump]$ tail -f conner_ckpt_2563.trc
WAIT #0: nam='rdbms ipc message' ela= 2994710 p1=300 p2=0 p3=0
WAIT #0: nam='control file parallel write' ela= 2442 p1=3 p2=3 p3=3
WAIT #0: nam='rdbms ipc message' ela= 2995171 p1=300 p2=0 p3=0
WAIT #0: nam='control file parallel write' ela= 2586 p1=3 p2=3 p3=3
WAIT #0: nam='rdbms ipc message' ela= 2994962 p1=300 p2=0 p3=0
WAIT #0: nam='control file parallel write' ela= 2582 p1=3 p2=3 p3=3
WAIT #0: nam='rdbms ipc message' ela= 2995020 p1=300 p2=0 p3=0
WAIT #0: nam='control file parallel write' ela= 2455 p1=3 p2=3 p3=3
WAIT #0: nam='rdbms ipc message' ela= 2995188 p1=300 p2=0 p3=0
WAIT #0: nam='control file parallel write' ela= 2412 p1=3 p2=3 p3=3
WAIT #0: nam='rdbms ipc message' ela= 2995187 p1=300 p2=0 p3=0
WAIT #0: nam='control file parallel write' ela= 2463 p1=3 p2=3 p3=3
WAIT #0: nam='rdbms ipc message' ela= 2995095 p1=300 p2=0 p3=0
WAIT #0: nam='control file parallel write' ela= 2448 p1=3 p2=3 p3=3
4.检查控制文件的变更
通过2次dump控制文件，比较其trace文件输出可以比较得到不同之处，我们发现，Oracle仅仅更新了Heartbeat这个数值。
[oracle@jumper udump]$ sqlplus "/ as sysdba"SQL*Plus: Release 9.2.0.4.0 - Production on Wed Jan 18 22:44:10 2006Copyright (c) 1982, 2002, Oracle Corporation. All rights reserved.Connected to:Oracle9i Enterprise Edition Release 9.2.0.4.0 - ProductionWith the Partitioning optionJServer Release 9.2.0.4.0 - Production
SQL> alter session set events 'immediate trace name CONTROLF level 10';Session altered.
SQL> exit
Disconnected from Oracle9i Enterprise Edition Release 9.2.0.4.0 - ProductionWith the Partitioning optionJServer Release 9.2.0.4.0 - Production[oracle@jumper udump]$ sqlplus "/ as sysdba"SQL*Plus: Release 9.2.0.4.0 - Production on Wed Jan 18 22:44:18 2006Copyright (c) 1982, 2002, Oracle Corporation. All rights reserved.Connected to:Oracle9i Enterprise Edition Release 9.2.0.4.0 - ProductionWith the Partitioning optionJServer Release 9.2.0.4.0 - ProductionSQL> alter session set events 'immediate trace name CONTROLF level 10' ;Session altered.SQL> exitDisconnected from Oracle9i Enterprise Edition Release 9.2.0.4.0 - ProductionWith the Partitioning optionJServer Release 9.2.0.4.0 - Production[oracle@jumper udump]$ lsconner_ora_21896.trc conner_ora_21898.trc[oracle@jumper udump]$ diff conner_ora_21896.trc conner_ora_21898.trc 1c1< /opt/oracle/admin/conner/udump/conner_ora_21896.trc---> /opt/oracle/admin/conner/udump/conner_ora_21898.trc14c14< Unix process pid: 21896, image: (TNS V1-V3)---> Unix process pid: 21898, image: (TNS V1-V3)16c16< *** SESSION ID9.813) 2006-01-18 22:44:14.314---> *** SESSION ID9.815) 2006-01-18 22:44:21.56963c63< heartbeat: 579991793 mount id: 3191936000---> heartbeat: 579991796 mount id: 3191936000 [oracle@jumper udump]$
Steve曾经这样描述CKPT Heartbeat:
In 8.0.5 a heartbeat mechanism was included in CKPT's timeout action (every 3 seconds) to update the checkpoint progress record for the thread in the controlfile.
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