hi,zhu chao=A3=A1
=09=09I think if the AIO is available ,then need not multiple dbwr=
. one DBWR can "use" more cpus and disk drivers . when os =
do not supports AIO ,one dbwr can only use a cpu and driver=
(even if there has more) per write. It waste the hard =
resource .
=09=09 yahoo id: feng_chunpei
msn: biti_rainy_at_hotmail.com
=A1=A1=A1=A1=A1=A1=A1=A1=A1=A1=A1=A1=A1=A1=A1=A1 biti_rainy_at_itpub.net
=A1=A1
>hi, friends:
> From time to time, I see various of notes say, in heavy=
load, you'd better use multiple dbwr even if AIO is used. I=
think AIO allows dbwr to issue new write request to the driver=
without waiting for the previous write request to complete.
> When disk itself is 100 busy, I think more dbwr won't=
help.If disk is not 100 busy, it is the oracle dbwr itself won't=
catch up, then we should use multiple dbwr. I did a performance=
test today, comparing the result of using 1 and 4 dbwr with aio=
on.
>Test Environment:
> Sun FireV880. 8*1.2GHZ CPU. 16G memory.
> Storage: HDS 9570.
> Oracle 8.1.7.4. Veritas Volume Manager 3.5. All=
datafile/redo/control/temp on raw device.
> Redo log size is 500M * 5 group.
> Shared_pool_size is 80M and data buffer is 1.2G.
>
>Build an empty database on raw device, with 25G of freespace.=
One target tablespace, extent management local uniform size 5m.
>Do a 1.2G dmp table import. No special tuning.
>
>First time: 1 dbwr. import. It took 20 minutes and 30 seconds.
>Second time: drop user, recreate user, configure 4 dbwr process,=
db_block_lru_latches=3D8.
> do import again..Time is 21Minutes and 44=
seconds.
>Third time: 1 dbwr. Drop user and recreate. The same parameter=
as test 1. (I did it as test 1, in case SAN cache was=
relatively empty, so maybe performance better).
> This time the import time is 21Minutes and 38=
seconds.
>
>There is no performance difference using 1 dbwr or 4 dbwr. I did=
a statspack, and found during peak time, there were 2500+ write=
per second. And according to the test, one dbwr can handle it=
efficiently. From solaris iostat -xn result, I saw 4000+ write=
per second during peak time(redo write plus dbwr write).
>
> I think import is a heavy task for dbwr, few database=
will write 2500+ per second(Our database do 200 write per=
second). Since in such a test, one dbwr can handle the request=
efficiently, I wonder whether those guys who claim the need for=
multiple dbwr do have real world experience, when aio is=
avaliable. If yes, please give us some data, not just the rule=
of the numb.
>
>Please comment.
>
>Regards
>Zhu Chao.
>
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Received on Sun Apr 18 2004 - 10:32:50 CDT