Queries Generating High "Cell Single Block Physical Read" Wait Messages
(Doc ID 2119510.1)
Last updated on MARCH 09, 2024
Applies to:
Oracle Database Backup Service - Version N/A and laterOracle Database - Enterprise Edition - Version 11.2.0.4 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 Cloud Infrastructure - Database Service - Version N/A and later
Information in this document applies to any platform.
Symptoms
Symptoms of this issue will appear as follows:
- Trace file entries that look similar to the following:
- The "Top 10 Foreground Events by Total Wait Time" section of the AWR report shows an exceedingly high number of waits but few to no average wait time. For example:
| Event | Waits | Total Wait Time (sec) | Wait Avg(ms) | % DB time | Wait Class |
| cell single block physical read | 19,654,319 | 4847,1 | 0 | 9.7 | User I/O |
- All or most of the events in the "Top SQL with Top Events" section of the ASH report are INDEX - STORAGE FAST FULL SCAN.
Cause
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