Oracle教程 2023-04-05

Oracle 视图 DBA_HIST_MTTR_TARGET_ADVICE 官方解释，作用，如何使用详细说明

本站中文解释

Oracle视图DBA_HIST_MTTR_TARGET_ADVICE被定义为一个用户可以查看的数据库内容，它提供了关于衡量数据库平均维护时间和建议的优化目标的信息。这个视图包含八列：SNAP_ID，DBID，TARGET_MTTR，TARGET_MTTRADVICE，AVG_MTTR，AVG_EXTRA_MTTR，AVG_EXTRA_TIME，DBTIME，和 TAKE_RATE。这些列允许用户查看平均维护时间，平均额外维护时间，平均数据库操作时间，以及衡量优化建议的目标MTTR时长。

要使用DBA_HIST_MTTR_TARGET_ADVICE视图，用户可以创建一个查询，用于从视图中获取特定的数据。以下是查询的一个示例：

SELECT SNAP_ID, DBID, TARGET_MTTR, TARGET_MTTRADVICE, AVG_MTTR, AVG_EXTRA_MTTR, AVG_EXTRA_TIME, DBTIME, TAKE_RATE
FROM DBA_HIST_MTTR_TARGET_ADVICE
WHERE DBID=my_dbid_number;

上面的查询将检索有关指定数据库的所有信息，这些信息将允许用户进行MTTR的分析，进而提出优化建议。

官方英文解释

DBA_HIST_MTTR_TARGET_ADVICE displays historical predictions of the number of physical I/O requests for the MTTR corresponding to each row.

The data also includes a physical I/O factor, which is the ratio of the number of estimated I/O requests to the number of I/O requests actually performed by the current MTTR setting during the measurement interval. This view contains snapshots of V$MTTR_TARGET_ADVICE.

Column	Datatype	NULL	Description
`SNAP_ID`	`NUMBER`	`NOT NULL`	Unique snapshot ID
`DBID`	`NUMBER`	`NOT NULL`	Database ID for the snapshot
`INSTANCE_NUMBER`	`NUMBER`	`NOT NULL`	Instance number for the snapshot
`MTTR_TARGET_FOR_ESTIMATE`	`NUMBER`		MTTR setting being simulated (equal to the current MTTR setting if this is the first row of the view)
`ADVICE_STATUS`	`VARCHAR2(5)`		Current status of MTTR simulation: `ON SET` `READY SET` `OFF`
`DIRTY_LIMIT`	`NUMBER`		Dirty buffer limit derived from the MTTR being simulated
`ESTD_CACHE_WRITES`	`NUMBER`		Estimated number of cache physical writes under the MTTR
`ESTD_CACHE_WRITE_FACTOR`	`NUMBER`		Estimated cache physical write ratio under the MTTR. It is the ratio of the estimated number of cache writes to the number of cache writes under the current MTTR setting.
`ESTD_TOTAL_WRITES`	`NUMBER`		Estimated total number of physical writes under the MTTR
`ESTD_TOTAL_WRITE_FACTOR`	`NUMBER`		Estimated total physical write ratio under the MTTR. It is the ratio of the estimated total number of physical writes to the total number of physical writes under the current MTTR setting.
`ESTD_TOTAL_IOS`	`NUMBER`		Estimated total number of I/O requests under the MTTR
`ESTD_TOTAL_IO_FACTOR`	`NUMBER`		Estimated total I/O ratio under the MTTR. It is the ratio of the estimated total number of I/O requests to the total number of I/O requests under the current MTTR setting.
`CON_DBID`	`NUMBER`		The database ID of the PDB for the sampled session
`CON_ID`	`NUMBER`		The ID of the container that `CON_DBID` identifies. Possible values include: `0`: This value is used for rows containing data that pertain to the entire CDB. This value is also used for rows in non-CDBs. `1`: This value is used for rows containing data that pertain to only the root n: Where n is the applicable container ID for the rows containing data

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