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database writer process [message #281295] Fri, 16 November 2007 06:22 Go to next message
RyjuRaju
Messages: 48
Registered: September 2007
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Hi
i would like to ask u if there is any relation between the number of database writer process and performance of the database.I found one article that increasing the number of database writer process will consume resource.So is that true?Is there any benefit in increasing the number of DBWRn.

many thanks
Ryju
Re: database writer process [message #281298 is a reply to message #281295] Fri, 16 November 2007 06:27 Go to previous messageGo to next message
JRowbottom
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It depends on the amount of writing that you need to do.
If your system generates a lot of Redo, and a lot of changes to the tables, then you'll need multiple DBWR processes.
If it's largely an enquiry system then you'll be able to get by on 1 or 2.
Re: database writer process [message #281299 is a reply to message #281298] Fri, 16 November 2007 06:28 Go to previous messageGo to next message
JRowbottom
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Registered: June 2006
Location: Sunny North Yorkshire, ho...
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Actually, what answer were you expecting?

Surely 10 seconds thought would lead you to the answer that if multiple DBWR processes just slowed your Db down, then there's be no point in having them.
Re: database writer process [message #281302 is a reply to message #281295] Fri, 16 November 2007 06:32 Go to previous messageGo to next message
Michel Cadot
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Quote:

increasing the number of database writer process will consume resource

Yes 2 processes consumes more resource than 1

Quote:

Is there any benefit in increasing the number of DBWRn.

If 1 DBWR can't do the job in time maybe 2 can do it.

Simple logic.

Regards
Michel
Re: database writer process [message #281304 is a reply to message #281295] Fri, 16 November 2007 06:35 Go to previous messageGo to next message
RyjuRaju
Messages: 48
Registered: September 2007
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thanks for the reply
Re: database writer process [message #281313 is a reply to message #281302] Fri, 16 November 2007 06:54 Go to previous messageGo to next message
martijn
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Registered: December 2006
Location: Netherlands
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Hi,

When reading this answer the following came up in my mind:

It's not very useful to have more dbwriter processes then there are CPU's (or even CPU cores).

Can someone comment on this?

Best regards,

Martijn
Re: database writer process [message #281320 is a reply to message #281313] Fri, 16 November 2007 07:08 Go to previous messageGo to next message
Michel Cadot
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CPU is not the first point of contention in this case (unless there is a great workload on the machine).
The main point is disk/controler.
Are DBWR able to write in parallel? Or are they concurrent and overload the disks?

Regards
Michel
Re: database writer process [message #281326 is a reply to message #281320] Fri, 16 November 2007 07:21 Go to previous message
martijn
Messages: 283
Registered: December 2006
Location: Netherlands
Senior Member
Tnx for the pointers.

I guess I have some reading/testing to do to find out, because I don't have an answer ready.

I guess it's also depending on the configuration of the disks/filesystems. (1 fs for 5 DBWR's will give more problems then 5 fs for 5DBWR's)

Once again thanks.

regards,
Martijn
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