Re:RE: Extents size.

From: <dgoulet_at_vicr.com>
Date: Tue, 02 Oct 2001 09:19:03 -0700
Message-ID: <F001.0039EF7D.20011002091529@fatcity.com>

Back in the V6 days it was a desired characteristic to have every thing in the first extent of an object for performance reasons. Thankfully those days are gone and it really does not matter how many extents there are. Rachel has a presentation on Oracle Myths where she actually portrays having multiple extents as a good thing from an IO perspective (Rachel, correct me if I got this wrong). Although I can't give you exact examples, take a look and v$filestat. I've found that tablespaces where there are more than one extent in the objects have a lower average io wait time that those where everything is in the first extent.

The only real good reason I have found for re-organizing a tablespace is to get all of the used extents at one end and all of the free extents (you know those little bitty ones that individually aren't worth the trouble, but together!!) at the other end.

Dick Goulet

____________________Reply Separator____________________
Author: Christopher Spence <cspence_at_FuelSpot.com>
Date:       10/2/2001 7:55 AM

That is completely a myth. There is no notable performance different with a table with 10,000 extents and one with 1.

The only problem is when it comes to the bitmaps when dealing with LMT and cluster when dealing with dictionary managed. When you query the extent views, or do space management type processes.

"Do not criticize someone until you walked a mile in their shoes, that way when you criticize them, you are a mile a way and have their shoes."

Christopher R. Spence
Oracle DBA
Phone: (978) 322-5744
Fax: (707) 885-2275

Fuelspot
73 Princeton Street
North, Chelmsford 01863

-----Original Message-----
Sent: Monday, October 01, 2001 7:15 PM
To: Multiple recipients of list ORACLE-L

May be it is good practice to keep number of extents to be less than 50, no matter what the size of extent.

-----Original Message-----
Sent: Monday, October 01, 2001 3:35 PM
To: Multiple recipients of list ORACLE-L

Hello,

I'll do an reorganization of a database (about 140 gigs). Some people say that it'd be good to use 128K, 4M and 128M extents. I saw somewhere it'd be 160K, 4M and 160M. Which size do you advice me ? I have also many small indexes (less than 16K).

Regards,

Thanh-truc Nguyen

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Author: Thanh-truc Nguyen
INET: truc_at_nguyen.as

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