RE: Locally managed tablespaces - autoallocate vs. uniform

From: Powell, Mark D <mark.powell_at_eds.com>
Date: Fri, 31 Jul 2009 15:01:31 -0400
Message-ID: <D1DC33E67722D54A93F05F702C99E2A90432484D_at_usahm208.amer.corp.eds.com>

The paper overstates the ability of locally managed tablespaces to eliminate free space fragmentation because while free space fragmentation is impossible with uniform extents since every extent is the desired size it is definitely possible with auto-allocate. The auto-allocate mythology breaks down when a file gets near its maximum size. All you need are a lot of little tables that extent over time and a few large tables that need big extents (8M, 64M). Over time the regular growth of the little tables cut enough 64K and 1M extents out of the free space that the large object cannot extend when the total free space is well in excess of the needed extent size. And while I have seen a request for a 64M extent stepped down I have never seen a request for a smaller size stepped down.  

If your file can extend you will not hit this issue, but if you file size is fixed or at maxsize you can hit this. Been there, done that.  

• Mark D Powell -- Phone (313) 592-5148

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        From: oracle-l-bounce_at_freelists.org
[mailto:oracle-l-bounce_at_freelists.org] On Behalf Of Allen, Brandon

	Sent: Friday, July 31, 2009 1:49 PM
	To: 'oracle-l_at_freelists.org'
	Subject: RE: Locally managed tablespaces - autoallocate vs.

uniform                  

        In case you don't have Metalink access, the same paper is available here:                   

http://www.oracle.com/technology/products/manageability/database/pdf/OOW 2002SpaceMgmtEXT.pdf          

        The pertinent section is on page 10.          

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Received on Fri Jul 31 2009 - 14:01:31 CDT