Solution : https://service.sap.com/sap/support/notes/1475173 (SAP Service marketplace login required)
Summary :
Oracle database instances utilizing auto-tuned undo retention under System Managed Undo (SMU) settings may experience significant waiting times due to "latch: row cache objects" and "enq: US - contention." This phenomenon is primarily observed with Oracle 10g onward. The contention typically occurs on dc_rollback_segments. To alleviate this, Oracle has introduced a fix in bug 7291739, which allows for setting a high threshold for undo retention periods through the "_highthreshold_undoretention" underscore parameter. This parameter is dynamically adjustable and caters to Oracle versions 10.2.0.5 onwards, supporting specific configurations for UNIX/LINUX and Windows systems. To prevent prolonged waits, disabling "_undo_autotune" and manually adjusting the undo_retention to reflect the estimated longest query time is advised, especially if ORA-1555 errors are encountered.
Key words :
terms 7291739 _undo_autotune _highthreshhold_undoretention spare _first_spare_parameter _sixth_spare_parameter latch enq ora-55567 reason, auto tuned undo retention period, disable auto tuning, _first_spare_parameter / _sixth_spare_parameter, row cache objects, system managed undo, alter system set, estimated maximum duration, low threshold retention, longest running query
Related Notes :
| 1475345 | Oracle 10.2.0.4 underscore spare parameter |
| 1468914 | ORA-55567 after install SAP Bundle Patch SAP_102044_201005 |
| 830576 | Parameter recommendations for Oracle 10g |
| 600141 | Oracle9i: Automatic UNDO Management |