v$db_cache_advice學習

shilei1發表於2012-04-08

v$db_cache_size用於判斷buffer_cache的大小是否合理，它受引數db_cache_advice引數影響，當db_chace_advice為on是測試開啟了buffer_cache的歐諾個級資訊的收集，供dba做出buffer_cache的調優工作。

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為buffer_pool組成部分的標識，例如keep_pool為1，recycle_pool為2等。

2、advice_status用於判斷advisor是否開啟，on表示開啟，off表示關閉。

3、size_for_estimate表示為預估的緩衝值的大小，單位是mb。

4、size_factor表示為預估的值與真實值的比較值。

5、ESTD_PHYSICAL_READ_FACTOR表示當buffer cache為size_for_estimate大小時，預估的物理讀的次數與當前實際的物理讀的次數的比值，如果當前物理讀為0的話，則此值為null。

6、ESTD_PHYSICAL_READS表示當緩衝池的大小為size_for_estimate時，需要的物理讀的大小。

7、estd_physical_read_time表示當緩衝池的大小為size_for_estimate是需要的物理讀的時間。

8、estd_pct_of_db_time_for_reads表示為當緩衝池為size_for_estimate是物理讀所消耗時間的百分比。

9、estd_cluster_reads表示為讀取的資料塊的總數。對rac有效

10、estd_cluster_read_time表示讀取花費的總時間。對rac有效

來自 “ ITPUB部落格 ” ，連結：http://blog.itpub.net/196700/viewspace-720647/，如需轉載，請註明出處，否則將追究法律責任。

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