Re: same udpate statement takes same cpu time but significant different "sequential read wait time"

Hi,

I can see both databases spend the majortiy of the time on 'db file sequential read' from the AWR. Another possiblity is that there are more disk contention on production than on the test database.

Thanks,
Qihua

On 9/30/07, Tony Adolph <tony.adolph.dba_at_gmail.com> wrote:
>
> Without too much thought, I'd say you're doing index lookups (db file
> sequential read') on one db and table scans (db file scattered read)
> on the other... are the stats up-to-date on both?
>
> Is there a particular update that's causing you a problem,...have you
> checked and compared the plans?
>
> I think I'd start there before going to the I/O system.
>
> HTH
> Tony
>
>
> On 9/30/07, qihua wu <staywithpin_at_gmail.com> wrote:
> > We have one test database another production database, the data volumn
> > nearly the small. But a single update statement takes about 2,000
> seconds on
> > test database, but 7,000 seconds on the productoin database. For the
> report
> > of OEM, both test database and production database take about 1,500
> seconds
> > on CPU. But the test database only takes 500 seconds on "sequential
> read"
> > and production database take 4,500 seconds on "sequential read".
> >
> > So I ran the following sql on the both database, and found that single
> > sequential read wait time on production is much longer than test
> database.
> > And I am wondering whether the IO subsystem in production is not as good
> as
> > test. What's your opinion on the big difference on "sequential read'?
> >
> > BTW,The unix team and SAN team are not easy to appoach, so I must gather
> > evidence to please them look into the IO subsystem. The sql result is
> only
> > from database level and they won't look at any evidence from database
> level.
> > Is there any standard unix tool that can test the "sequential read'
> speed?
> >
> > select
> > sum(a.time_waited_micro)/sum(a.total_waits)/1000000 c1,
> > sum(b.time_waited_micro)/sum(b.total_waits)/1000000 c2,
> > from
> > dba_hist_system_event a,
> > dba_hist_system_event b
> > where
> > a.snap_id = b.snap_id
> > and
> > a.event_name = 'db file scattered read'
> > and
> > b.event_name = 'db file sequential read';
> >
>

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