Fixed Objects Statistics (GATHER_FIXED_OBJECTS_STATS) Considerations
(Doc ID 798257.1)
Last updated on MAY 26, 2020
Applies to:Oracle Database Cloud Exadata Service - Version N/A and later
Oracle Database Cloud Schema Service - Version N/A and later
Gen 1 Exadata Cloud at Customer (Oracle Exadata Database Cloud Machine) - Version N/A and later
Oracle Database Exadata Express Cloud Service - Version N/A and later
Oracle Database Cloud Service - Version N/A and later
Information in this document applies to any platform.
- Missing or bad statistics on the X$ / fixed tables can lead to performance degradation or hangs. Various X$ views are protected by latches and as a result can be very expensive to query in large / busy systems.
- Most commonly this issue is seen on the underlying X$ tables for DBA_EXTENTS, V$ACCESS, V$RMAN_BACKUP_JOB_DETAILS, and V$RMAN_STATUS, but any fixed table protected through latching can experience this.
- Another commonly seen symptom is extreme TEMP space usage driven by poor plans against the fixed tables.
- RMAN, Data Guard, Streams, and Grid Control make heavy usage of the fixed tables through the DBA/V$ views and so can often bear the brunt of performance issues.
- These are not an exhaustive list of symptoms. Any item using X$ views and getting bad plans may be experiencing poor plans because of missing or bad statistics.
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