High US - contention enqueue / rowcache lock while trying to online a NEW undo segment
(Doc ID 1577753.1)
Last updated on FEBRUARY 20, 2025
Applies to:
Oracle Database - Enterprise Edition - Version 10.2.0.4 to 11.1.0.7 [Release 10.2 to 11.1]Oracle Database Cloud Schema Service - Version N/A and later
Oracle Database Exadata Cloud Machine - Version N/A and later
Oracle Cloud Infrastructure - Database Service - Version N/A and later
Oracle Database Backup Service - Version N/A and later
Information in this document applies to any platform.
Symptoms
High US - contention enqueue , latch: row cache objects and rowcache locks may be seen while trying to online a new undo segment.
When transaction concurrency increases sharply (e.g. following a connection storm or high DML activity), Automatic UNDO Management (AUM) may need to bring online existing undo segments, or create additional undo segments.
The process of creating additional undo segments or onlining existing undo segments appears to be slower in 11.1.0.6 than in 10.2.0.3 .
The Test Case Done for the Bug Investigation creates 1782 undo segments in first run on freshly created db and onlines 1782 undo segments in second run .
The Following are the Test Case results , which shows slight increase in the Database Time , slight increase in US enqueue while onlining ,
and Huge increase in latch: row cache objects wait time in both scenarios (creating or onlining undo segments)
| Wait Event time create undo segments | 10.2.0.3 | 11.1.0.6 |
|---|---|---|
| DB time | 5538 | 6375 |
| DB CPU | 164 | 151 |
| US - contention | 4636 | 2587 |
| row cache objects latch | 96 | 3434 |
| row cache lock wait time | 569 | 169 |
| latch free wait time | 58 | 118 |
| Wait Event time onlining undo segments | 10.2.0.3 | 11.1.0.6 |
|---|---|---|
| DB time | 2019 | 2190 |
| DB CPU | 58 | 53 |
| US - contention | 1141 | 1532 |
| row cache objects latch | 98 | 226 |
| row cache lock | 667 | 313 |
| latch free | 28 | 178 |
Cause
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In this Document
| Symptoms |
| Cause |
| Solution |
| References |