RE: Locally managed tablespaces - autoallocate vs. uniform
- From: "Powell, Mark D" <mark.powell@xxxxxxx>
- To: <Brandon.Allen@xxxxxxxxxxx>, <oracle-l@xxxxxxxxxxxxx>
- Date: Fri, 31 Jul 2009 15:01:31 -0400
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
________________________________
From: oracle-l-bounce@xxxxxxxxxxxxx
[mailto:oracle-l-bounce@xxxxxxxxxxxxx] On Behalf Of Allen, Brandon
Sent: Friday, July 31, 2009 1:49 PM
To: 'oracle-l@xxxxxxxxxxxxx'
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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