Oracle教程 2023-04-02

Oracle 视图 V$PGA_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V$PGA_TARGET_ADVICE是可以用来分析查看根据你给出的PGA_TARGET_FACTOR，接着系统给出推荐的PGA设置来改善系统效率的视图。其中PGA_TARGET_FACTOR由用户设定，表明当前连接要占用PGA内存的比例；推荐的PGA_TARGET设置应该使系统最大程度的提高，操作的系统效率。

用户可以使用V$PGA_TARGET_ADVICE视图来侦测和调整PGA内存的设置，来改善Oracle数据库的性能。例如，执行以下查询来检查当前的PGA_TARGET的值：

SELECT pga_target_for_estimate, pga_target_factor, estd_pga_target_cache_miss_percentage FROM v$pga_target_advice;

执行这段代码后，会得到当前PING_TARGET的值，当前的PGA_TARGET_FACTOR，以及推荐的PGA_TARGET_CACHE_MISS_PERCENTAGE。

官方英文解释

V$PGA_TARGET_ADVICE predicts how the cache hit percentage and over allocation count statistics displayed by the V$PGASTAT performance view would be impacted if the value of the PGA_AGGREGATE_TARGET parameter is changed.

The prediction is performed for various values of the PGA_AGGREGATE_TARGET parameter, selected around its current value. The advice statistic is generated by simulating the past workload run by the instance.

The content of the view is empty if PGA_AGGREGATE_TARGET is not set. In addition, the content of this view is not updated if the STATISTICS_LEVEL parameter is set to BASIC. Base statistics for this view are reset at instance startup and when the value of the PGA_AGGREGATE_TARGET initialization parameter is dynamically modified.

Column	Datatype	Description
`PGA_TARGET_FOR_ESTIMATE`	`NUMBER`	Value of `PGA_AGGREGATE_TARGET` for this prediction (in bytes)
`PGA_TARGET_FACTOR`	`NUMBER`	`PGA_TARGET_FOR_ESTIMATE` / the current value of the `PGA_AGGREGATE_TARGET` parameter
`ADVICE_STATUS`	`VARCHAR2(3)`	Indicates whether the advice is enabled (`ON`) or disabled (`OFF`) depending on the value of the `STATISTICS_LEVEL` parameter
`BYTES_PROCESSED`	`NUMBER`	Total bytes processed by all the work areas considered by this advice (in bytes)
`ESTD_TIME`	`NUMBER`	Time (in seconds) required to process the bytes
`ESTD_EXTRA_BYTES_RW`	`NUMBER`	Estimated number of extra bytes which would be read or written if `PGA_AGGREGATE_TARGET` was set to the value of the `PGA_TARGET_FOR_ESTIMATE` column. This number is derived from the estimated number and size of work areas which would run in one-pass (or multi-pass) for that value of `PGA_AGGREGATE_TARGET`.
`ESTD_PGA_CACHE_HIT_PERCENTAGE`	`NUMBER`	Estimated value of the cache hit percentage statistic when `PGA_AGGREGATE_TARGET` equals `PGA_TARGET_FOR_ESTIMATE`. This column is derived from the above two columns and is equal to `BYTES_PROCESSED` / (`BYTES_PROCESSED` + `ESTD_EXTRA_BYTES_RW`)
`ESTD_OVERALLOC_COUNT`	`NUMBER`	Estimated number of PGA memory over-allocations if the value of `PGA_AGGREGATE_TARGET` is set to `PGA_TARGET_FOR_ESTIMATE`. A nonzero value means that `PGA_TARGET_FOR_ESTIMATE` is not large enough to run the work area workload. Hence, the DBA should not set `PGA_AGGREGATE_TARGET` to `PGA_TARGET_FOR_ESTIMATE` since Oracle will not be able to honor that target.
`CON_ID`	`NUMBER`	The ID of the container to which the data pertains. 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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