Your database instance is functional for the past one month. The Automatic Workload Repository (AWR) snapshot retention is set to 7 and the STATISTICS_LEVEL initialization parameter is set to…

The in-memory ASH buffer holds only the most recent hour of session samples, and while AWR persists a subset of ASH data, ASH reports target near-real-time diagnosis rather than structured historical investigation of a prior-day incident.

The AWR Compare Periods report compares two distinct time periods - such as the problematic 7-9 PM window against a normal reference period - highlighting statistical differences that reveal the source of degradation.

ADDM automatically analyzes AWR snapshot data for a specified historical range and produces ranked bottleneck findings with recommendations; since AWR retains 7 days of snapshots, the previous day's 7-9 PM window is fully available for ADDM analysis.

The AWR Compare Period report requires two separate time ranges to produce meaningful comparative output; specifying only a single period (7 PM to 9 PM of the previous day) without a second baseline period yields no comparative diagnostic value.