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Db writer Process [message #378925]

Fri, 02 January 2009 12:37

dbcop
Messages: 37
Registered: September 2006
Location: india

Member

Env: AIX Database Version:9.2.0.7

I have been newly assigned to handle a production server with 4 TB data . I found there are 12 DB writer processes running but I need to know if the number is appropriately identified or can we reduce it. Please let me know what are the factors that I should consider to determine it. Asynch IO also were not of good help so I understand configuring mutliple DBws is required but to an extent of 12 seems to be on the higher side although I know 20 DBws r supported (probably in 10 g).
Total no of CPU running is 9 all dedicated.

I hv the statspack report so if anybody wants I can share it.
Top five events include DB file sequential read,Log File Sync,Buffer Busy wait to mention few.

Thanks

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Re: Db writer Process [message #378926 is a reply to message #378925]

Fri, 02 January 2009 12:46

BlackSwan
Messages: 26766
Registered: January 2009
Location: SoCal

Senior Member

Why did you focus on DB Writer process as opposed to any of the other gazillion of parts of Oracle which also impact performance?

What problem are you really trying to solve?

How would an independent observer conclude (base upon which metric & what value) that "your problem" has been solved?

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Re: Db writer Process [message #378930 is a reply to message #378925]

Fri, 02 January 2009 13:58

Michel Cadot
Messages: 68716
Registered: March 2007
Location: Saint-Maur, France, https...

Senior Member
Account Moderator

DB file sequential read -> read -> not DB Writer
Log File Sync -> Wait for log -> LGWR -> no DB Writer
Buffer Busy wait -> Users wait to access buffer blocks -> not DB Writer

Forget DB Writer and start reading spdoc.txt and Database Performance Tuning Guide.

Regards
Michel

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Re: Db writer Process [message #378948 is a reply to message #378925]

Sat, 03 January 2009 00:24

dbcop
Messages: 37
Registered: September 2006
Location: india

Member

Gentleman

I completely agree with you that the top events doesn't indicate for DB writer process I am aware of it.

Pls understand I am looking all the other factors for performance improvement it is not only the DB writer that I am looking into.

I understand it is difficult for you to predict solution I am not expecting that either.

In an attenmpt to reduce process overehead on the server I was looking into the DBwr process .

I will take care of all the other factors (top events) I am quite capable of doing that.

My question was if it were you to determine the apropriate number of DBwr what are things that you will consider before defining the number in a 4 TB database? what are the metrics data that you should look into ?

Anyways Thanks to all who replied.

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Re: Db writer Process [message #378949 is a reply to message #378925]

Sat, 03 January 2009 00:29

dbcop
Messages: 37
Registered: September 2006
Location: india

Member

Even though I need to reduce process overhead on the server but I cannot switch to shared server mode . It is not possibe in the env we are working have analyzed it as well.

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Re: Db writer Process [message #378979 is a reply to message #378949]

Sat, 03 January 2009 06:57

Mahesh Rajendran
Messages: 10708
Registered: March 2002
Location: oracleDocoVille

Senior Member
Account Moderator

This article in two parts will be good read for you.

http://kevinclosson.wordpress.com/2007/08/10/learn-how-to-obliterate-processor-caches-configure-lots-and-lots-of-dbwr-processes/

http://kevinclosson.wordpress.com/2007/08/17/over-configuring-dbwr-processes-part-ii/

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Re: Db writer Process [message #378991 is a reply to message #378925]

Sat, 03 January 2009 10:16

BlackSwan
Messages: 26766
Registered: January 2009
Location: SoCal

Senior Member

http://www.orafaq.com/forum/t/84315/74940/
which have you tried & what were the results

How would an independent observer conclude (base upon which metric & what value) that "your problem" has been solved?

[Updated on: Sat, 03 January 2009 13:24]

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