RE: Setting PCTFREE & PCTUSED in a Datawarehouse

From: Vikas Kawatra <VKawatra_at_innoventry.com>
Date: Fri, 29 Jun 2001 13:22:56 -0700
Message-ID: <F001.0033E1C9.20010629132142@fatcity.com>

Thanks Lisa !

-----Original Message-----
Sent: Friday, June 29, 2001 10:21 AM
To: 'ORACLE-L_at_fatcity.com'; 'vkawatra_at_innoventry.com'

Hi Vikas,

The docs should have discussed the reason why. High pctused can lead to a block going on and off the freelist frequently as deletes/inserts are processed, and also can leave the amount of free space inadequate for a new insert (your avg_rowlen comes into play here). So what you'd end up with is several blocks on the freelist that don't have enough free space for an insert, and every time an insert is processed it goes thorugh the freelist and checks for space in the block. The performance hit comes when too many blocks have to be checked for adequate space. Does that make sense?

Now some people on this list have debated that PCTFREE/PCTUSED is so low level and that performance really is not affected that much. Of course Ross was one of those people ("amen, my brother")

HTH
Lisa Koivu
Data Bored Administrator
Ft. Lauderdale, FL, USA

-----Original Message-----
Sent: Friday, June 29, 2001 11:42 AM
To: Multiple recipients of list ORACLE-L

I read in the Oracle docs that setting a high PCTUSED ( such as 60/70) would
increase the cost of INSERTS to the table. Can someone explain this , pleas e!

thanks

vikas
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Author: Vikas Kawatra
INET: VKawatra_at_innoventry.com

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Author: Vikas Kawatra
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