DBA_HIST_PGA_TARGET_ADVICE displays historical predictions of how the cache hit percentage and over allocation count statistics displayed by the V$PGASTAT performance view would be impacted if the value of the PGA_AGGREGATE_TARGET parameter is changed. This view contains snapshots of V$PGA_TARGET_ADVICE.
Unique snapshot ID
Database ID for the snapshot
Instance number for the snapshot
Value of PGA_AGGREGATE_TARGET for the prediction (in bytes)
PGA_TARGET_FOR_ESTIMATE / the current value of the PGA_AGGREGATE_TARGET parameter
Indicates whether the advice is enabled (ON) or disabled (OFF) depending on the value of the STATISTICS_LEVEL parameter
Total bytes processed by all the work areas considered by this advice (in bytes)
Time (in seconds) required to process the bytes
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.
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)
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, PGA_AGGREGATE_TARGET should not be set to PGA_TARGET_FOR_ESTIMATE since Oracle will not be able to honor that target.