Re: "cache buffer chains" misses > 0 and spins & sleep[1-4] are zero, yet sleeps > 0
- From: Jared Still <jkstill@xxxxxxxxx>
- To: kutrovsky.oracle@xxxxxxxxx
- Date: Mon, 6 Jun 2005 10:11:23 -0700
Hi Chris,
For the short answer, see http://www.ixora.com.au/q+a/latches.htm.
Oracle spins then sleeps if the spin did not obtain a latch.
With a request:miss ratio of 15249:1 and 133 spins that successfully
obtained the latch, I am wondering if this is considered a performance
problem, or an academic exercise?
--
Jared Still
Certifiable Oracle DBA and Part Time Perl Evangelist
On 6/4/05, Christo Kutrovsky <kutrovsky.oracle@xxxxxxxxx> wrote:
>
> Hello all,
>
> Latch Sleep breakdown for DB: WEBP1 Instance: webp1 Snaps: 32412 -32413
> -> ordered by misses desc
>
> Get Spin &
> Latch Name Requests Misses Sleeps Sleeps 1-=
> >4
> -------------------------- -------------- ----------- -----------
> ---------=
> ---
> ...
> cache buffers chains 30,194,375 1,980 133 0/0/0/0/0
> ...
>
> I am looking at this statspack extract over 20 minutes. I have a very
> specific question.
>
> Given that I have ~2000 misses and 133 sleeps, howcome I dont have
> anything in spins and sleeps[1-4] ?
>
> Are the cache buffer chains special, i.e. there is no spinning to
> acquire them ? And if there are sleeps, last column is supposed to be
> 4 or more, yet it is still zero?
>
> Looking in v$latch:
>
> ADDR=095000D3E0
> LATCH#=0998
> LEVEL#=091
> NAME=09cache buffers chains
> GETS=09113996341015
> MISSES=09286248205
> SLEEPS=092787346
> IMMEDIATE_GETS=093233325716
> IMMEDIATE_MISSES=0912384650
> WAITERS_WOKEN=090
> WAITS_HOLDING_LATCH=092933754
> SPIN_GETS=090
> SLEEP1=090
> SLEEP2=090
> SLEEP3=090
> SLEEP4=090
> SLEEP5=090
> SLEEP6=090
> SLEEP7=090
> SLEEP8=090
> SLEEP9=090
> SLEEP10=090
> SLEEP11=090
> WAIT_TIME=090
>
>
> You can see there's a large number of gets/misses but NONE in
> spin_gets and sleeps 1-4, why is that ?
>
>
>
--
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