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v$db_cache_advice学习

原创 Linux操作系统 作者:shilei1 时间:2012-04-08 04:41:54 0 删除 编辑

v$db_cache_size用于判断buffer_cache的大小是否合理,它受参数db_cache_advice参数影响,当db_chace_advice为on是测试打开了buffer_cache的欧诺个级信息的收集,供dba做出buffer_cache的调优工作。

V$DB_CACHE_ADVICEcontains rows that predict the number of physical reads for the cache size corresponding to each row. The rows also compute a "physical read factor," which is the ratio of the number of estimated reads to the number of reads actually performed by the real buffer cache during the measurement interval.

ColumnDatatypeDescription
IDNUMBERBuffer pool identifier (ranges from 1 to 8)
NAMEVARCHAR2(20)Buffer pool name
BLOCK_SIZENUMBERBlock size in bytes for buffers in this pool. Possible values: the standard block size, the power of 2 non-standard block sizes,2048,4096,8192,16384,32768.
ADVICE_STATUSVARCHAR2(3)Status of the advisory.ONindicates it is currently running;OFFindicates it is disabled (in this case the estimates are historical and calculated when last enabled).
SIZE_FOR_ESTIMATENUMBERCache size for prediction (in megabytes)
SIZE_FACTORNUMBERSize factor with respect to the current cache size
BUFFERS_FOR_ESTIMATENUMBERCache size for prediction (in terms of buffers)
ESTD_PHYSICAL_READ_FACTORNUMBERPhysical read factor for this cache size, which is the ratio of the number of estimated physical reads to the number of reads in the real cache. If there are no physical reads in the real cache, the value of this column is null.
ESTD_PHYSICAL_READSNUMBEREstimated number of physical reads for this cache size
ESTD_PHYSICAL_READ_TIMENUMBEREstimated disk read time
ESTD_PCT_OF_DB_TIME_FOR_READSNUMBEREstimated disk time as a percentage of the total time
ESTD_CLUSTER_READSNUMBEREstimated total number of blocks foreground processes read from the global cache (Real Application Clusters only)
ESTD_CLUSTER_READ_TIMENUMBEREstimated total amount of time, in seconds, foreground processes read from global cache (Real Application Clusters only)

1、ID为buffer_pool组成部分的标识,例如keep_pool为1,recycle_pool为2等。

2、advice_status用于判断advisor是否打开,on表示打开,off表示关闭。

3、size_for_estimate表示为预估的缓冲值的大小,单位是mb。

4、size_factor表示为预估的值与真实值的比较值。

5、ESTD_PHYSICAL_READ_FACTOR表示当buffer cache为size_for_estimate大小时,预估的物理读的次数与当前实际的物理读的次数的比值,如果当前物理读为0的话,则此值为null。

6、ESTD_PHYSICAL_READS表示当缓冲池的大小为size_for_estimate时,需要的物理读的大小。

7、estd_physical_read_time表示当缓冲池的大小为size_for_estimate是需要的物理读的时间。

8、estd_pct_of_db_time_for_reads表示为当缓冲池为size_for_estimate是物理读所消耗时间的百分比。

9、estd_cluster_reads表示为读取的数据块的总数。对rac有效

10、estd_cluster_read_time表示读取花费的总时间。对rac有效

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