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 thePGA_AGGREGATE_TARGET
initialization parameter using the PGA advice views