MTTR advisory is disabled because FAST_START_MTTR_TARGET is not set
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查看alert日志,有MTTR advisory is disabled because FAST_START_MTTR_TARGET is not set这样的提示
配置高速缓存恢复的持续时间:FAST_START_MTTR_TARGET
快速启动故障恢复的基础是快速启动检查点的架构。而不是传统的事件驱动(也就是日志切换)检查点,这的确批量写入,快速启动检查点逐渐发生。每个DBWn进程定期写入缓冲区写入磁盘,推进检查点位置。最古老的修改过的块被写入首先要保证每一个写使检查点前进。快速启动检查点消除了与传统检查点发生大量写入和由此产生的I / O峰值。
随着快速启动故障恢复功能,FAST_START_MTTR_TARGET初始化参数,简化了恢复时间的配置从实例或系统故障。FAST_START_MTTR_TARGET指定预期的平均恢复时间(MTTR)的目标,也就是说,时间(以秒为单位)它应该启动实例并进行高速缓存恢复。一旦FAST_START_MTTR_TARGET被设置,数据库管理增量检查点写在试图满足该目标。如果你选择了一个有实用价值的FAST_START_MTTR_TARGET,你可以期望你的数据库恢复,平均而言,在几秒钟之约你所选择的号码。
注意:
如果使用时初始化参数FAST_START_MTTR_TARGET,必须禁用或删除FAST_START_IO_TARGET,LOG_CHECKPOINT_INTERVAL和LOG_CHECKPOINT_TIMEOUT
FAST_START_MTTR_TARGET最大值是3600秒(1小时)。如果设置的值超过3600,则Oracle四舍五入到3600秒。
我们可以使用下面方式设置FAST_START_MTTR_TARGET的值:
SQL>ALTER SYSTEM SET FAST_START_MTTR_TARGET=30;
当FAST_START_MTTR_TARGET参数未设置时,自动检查点调整生效。
通常,如果我们必须严格控制实例或节点恢复时间,那么我们可以设置FAST_START_MTTR_TARGET为期望时间值;如果恢复时间不需要严格控制,那么我们可以不设置FAST_START_MTTR_TARGET参数,从而启用Oracle10g的自动检查点调整特性。
SQL> show parameter fast_start_mttr
NAME TYPE VALUE
------------------------------------ ----------- ------------------------------
fast_start_mttr_target integer0
FAST_START_MTTR_TARGET的值为0,即设置为自动检测点调整
从v$instance_recovery视图,查看FAST_START_MTTR_TARGET
SQL> select RECOVERY_ESTIMATED_IOS REIOS,TARGET_MTTR TMTTR,
2 ESTIMATED_MTTR EMTTR,WRITES_MTTR WMTTR,WRITES_OTHER_SETTINGS WOSET,
3 CKPT_BLOCK_WRITES CKPTBW,WRITES_AUTOTUNE WAUTO,WRITES_FULL_THREAD_CKPT WFTCKPT
4 from v$instance_recovery;
REIOS TMTTR EMTTR WMTTR WOSET CKPTBW WAUTO WFTCKPT
---------- ---------- ---------- ---------- ---------- ---------- ---------- ----------
49407 0 68 0 0 3649819 3506125 3130700
在以上视图中,WRITES_AUTOTUNE字段值就是指由于自动调整检查点执行的写出次数,
而CKPT_BLOCK_WRITES指的则是由于检查点写出的Block的数量。
具体信息,可以参考官方文档
http://docs.oracle.com/cd/B19306_01/backup.102/b14191/rcmtunin.htm#i1015453
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