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Oracle® Database Reference 10g Release 2 (10.2) Part Number B14237-02 |
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# V$PGA_TARGET_ADVICE

`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_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.

See Also: Oracle Database Performance Tuning Guide for information on tuning the `PGA_AGGREGATE_TARGET` initialization parameter using the PGA advice views