Re: US Enqueue , latch row object cache - performance issue

From: Charles Hooper <hooperc2000_at_yahoo.com>
Date: Tue, 11 Aug 2009 11:13:20 -0700 (PDT)
Message-ID: <cdc2f373-a268-4c8b-8a8c-4d6b72effece_at_s15g2000yqs.googlegroups.com>

On Aug 11, 12:35 pm, Grzegorz <grzegor..._at_interia.pl> wrote:
> Hi,
>
>    one of our 9.2.0.8 EE databse suffered from US enqueue contention.
> Scenario was:
> 1. NOSPACEERRCNT in v$undostat suddenly showed 200 with high UNX% EXP%
> columns values  (10 000 - 20 000)
> 2. v$session_wait showed about 30 session with enqueue US type waits and
> about 22 latch waits (type row cache object )
(snip)
> Best regards.
> Greg

Greg,

Take a look at Metalink Doc ID 463136.1 "POOR PERFORMANCE DUE TO HUGE WAITS ON US ENQUEUE" which applies to versions 9.0.1.4 to 9.2.0.8. Doc ID 301432.1 "Performance Slowdown During Heavy Undo Segment Onlining" states that it applies to 9.2.0.5, but the work-around is almost the same as for Doc ID 463136.1.

An advanced Metalink search for the phrase "US enqueue" finds several other related documents.

Charles Hooper
IT Manager/Oracle DBA
K&M Machine-Fabricating, Inc. Received on Tue Aug 11 2009 - 13:13:20 CDT