Re: "latch: cache buffers chains" wait in NON-RAC Benchmark Runs
- From: "Brian MacLean" <bpmaclean.oracle@xxxxxxxxx>
- To: VIVEK_SHARMA@xxxxxxxxxxx
- Date: Fri, 15 Feb 2008 08:09:46 -0700
See
http://www.dba-oracle.com/t_high_cache_buffer_chain_waits_contention.htm
and the text below is from
http://www.quest-pipelines.com/newsletter-v5/Resolving_Oracle_Latch_Contention.pdf
*
Avoiding Hot Blocks
*
Cache buffers chains latch contention is one of the most intractable types
of latch contention.
There are a couple of things you can do at the application level to reduce
the severity of this type of contention.
Firstly, identify the blocks that are "hot." Metalink note 163424.1, "How to
Identify a Hot
Block Within The Database" describes how to do this. Having identified the
identity of the hot block, you will most likely find that it is an index
root or branch block. If this is the case, there are two application design
changes that may help.
1) Consider partitioning the table and using local indexes. This might allow
you to spread the heat amongst multiple indexes (you will probably want to
use a hash partition to ensure an even spread of load amongst the
partitions).
2) Consider converting the table to a hash cluster keyed on the columns of
the index. This allows the index to be bypassed completely and may also
result in some other performance improvements. However, hash clusters are
suitable only for tables of relatively static size, and determining an
optimal setting for the SIZE and HASHKEYS storage parameters are essential.
On 2/14/08, VIVEK_SHARMA <VIVEK_SHARMA@xxxxxxxxxxx> wrote:
>
>
> Folks
>
> In a Benchmark Run, 512 concurrent BATCH Processes using Dedicated
> Sessions (NON-MTS) showing the following Waits:-
>
> How is the "latch: cache buffers chains" wait to be addressed?
>
> Should "_write_clones" be set to "0"
> Current default value is "3"
>
> Will share the Statspack Report, as needed.
>
> Config:-
> Oracle 10.2.0.3 ( NON-RAC )
> Solaris 10
>
> Cheers
>
> Vivek
>
> Statspack Report :-
>
> Elapsed: 19.23 (mins)
>
> Top 5 Timed Events Avg
> %Total
> ~~~~~~~~~~~~~~~~~~
> wait Call
> Event Waits Time (s)
> (ms) Time
> ----------------------------------------- ------------ ----------- ------
> ------
> CPU
> time 28,932
> 27.2
> latch: cache buffers chains 379,062 18,092
> 48 17.0
> db file scattered read
> 134,021 17,649 132 16.6
> db file sequential read 155,494 13,199
> 85 12.4
> SQL*Net break/reset to
> client 4,314,656 10,430 2 9.8
> -------------------------------------------------------------
> ^LHost CPU (CPUs: 120)
> ~~~~~~~~ Load Average
> Begin End User System Idle WIO
> WCPU
> ------- ------- ------- ------- ------- -------
> --------
> 1.55 6.65
> 40.30 30.85 28.84 0.00 77.42
>
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