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"LATCH: UNDO GLOBAL DATA" In The Top Wait Events (Doc ID 1451536.1)

Last updated on JULY 03, 2023

Applies to:

Oracle Database - Enterprise Edition - Version 11.1.0.6 and later
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 Exadata Express Cloud Service - Version N/A and later
Information in this document applies to any platform.Symptoms

An AWR report shows the following statistics:

  • The "Top 5 Timed Foreground Events" section shows "latch: undo global data" waits:
    EventWaitsTime(s)Avg wait (ms)% DB timeWait Class
    latch: undo global data 5,257,419 112,705 21 61.26 Other
    enq: US - contention 3,190,797 49,454 15 26.88 Other
    DB CPU   14,686   7.98  
    buffer busy waits 926,370 3,912 4 2.13 Concurrency
    log file sync 1,515,418 1,760 1 0.96 Commit
  • The "Latch Miss Sources" section shows "ktusm_stealext_2":
    Latch NameWhereNoWait MissesSleepsWaiter Sleeps
    undo global data ktusm_stealext_2 0 5,369,570 4,676,871
    undo global data ktusmupst: KSLBEGIN 0 134,048 368,708
    undo global data ktusm_stealext: KSLBEGIN 0 98,480 103,560
    undo global data ktuGetRetentionDuration 0 76,472 86,911
    undo global data ktusmasp: ktugd_tuux 0 58,548 125,526
    undo global data ktudba: KSLBEGIN 0 14,221 349,885
  • The undo related instance parameters are set as follows:
    • _undo_autotune = false
    • undo_management = auto
    • undo_retention = 10800

Cause

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