CKPT相关知识
更新时间：2014年4月12日 7:59:39
★ 发生CKPT场景
1. Consistent database shutdown，如： shutdown IMMEDIATE
2. Online Redo log 切换时
3. ALTER SYSTEM CHECKPOINT
4. ALTER DATABASE BEGIN BACKUP
5. Tablespace and data file checkpoints（Tablespace and data file checkpoints，including making a tablespace read-only or taking it offline normal, shrinking a data file, or executing ALTER TABLESPACE BEGIN BACKUP）
6. DBWn每三秒检查一次是否有有需要写入的数据
7. DBWn writes dirty buffers，causing CKPT to write the checkpoint position to the control file, but not to the data file headers.
8. Other types of checkpoints include instance and media recovery checkpoints and checkpoints when schema objects are dropped or truncated
★ CKPT
发生CKPT后，将会修改Control File及Data File Header
★ 相关文档
FAST_START_MTTR_TARGET enables you to specify the number of seconds the database takes to perform crash recovery of a single instance. When specified, FAST_START_MTTR_TARGET is overridden by LOG_CHECKPOINT_INTERVAL.
-- LOG_CHECKPOINT_INTERVAL会覆盖FAST_START_MTTR_TARGET的设定值
LOG_CHECKPOINT_INTERVAL specifies the frequency of checkpoints in terms of the number of redo log file blocks that can exist between an incremental checkpoint and the last block written to the redo log. This number refers to physical operating system blocks, not database blocks.
Regardless of this value, a checkpoint always occurs when switching from one online redo log file to another. Therefore, if the value exceeds the actual redo log file size, checkpoints occur only when switching logs. Checkpoint frequency is one of the factors that influence the time required for the database to recover from an unexpected failure.
Notes:
· Specifying a value of 0 (zero) for LOG_CHECKPOINT_INTERVAL has the same effect as setting the parameter to infinity and causes the parameter to be ignored. Only nonzero values of this parameter are considered meaningful.
· Recovery I/O can also be limited by setting the LOG_CHECKPOINT_TIMEOUT parameter or by the size specified for the smallest redo log. For information on which mechanism is controlling checkpointing behavior, query the V$INSTANCE_RECOVERY view.
★ 问题
1. 频繁checkpoint的解决
加大日志文件；
加大 FAST_START_MTTR_TARGET，最大3600 (秒)；
