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RE: Extent allocation

From: Yttri, Lisa <>
Date: Fri, 09 Feb 2001 09:20:08 -0800
Message-ID: <>

I found a document on metalink   #69343.1 that pretty much explains it.  Unfortunately, it makes it sound like you can never be sure of the sizing you choose, because it looks at the size of the first two open blocks, rather than finding a block that fits what you want.

Am I missing something?
From: Shakeel Qureshi
To: Multiple recipients of list ORACLE-L Subject: RE: Extent allocation
Date: Thursday, February 08, 2001 1:34PM

Hi Paul,

I created an object with initial_extent 128K and it took 13 blocks.  I then created the same object with 208K and still it took 13 blocks.  My db_block size is 16K.  I tested this on 8.1.5 and 8.1.6 and they both behave the same.

TIA, Shakeel Qureshi
 --- Paul Baumgartel <> wrote:
> It is a big clue.  Oracle rounds to multiples of 5
> extents to prevent the
> existence of a free extent of fewer than 5 blocks,
> which is unlikely to be
> usable.
> Paul Baumgartel
> InstiPro, Inc.
> 212 813-0829 x103 (office)
> 917 549-4717         (mobile)
> -----Original Message-----
> Sent: Wednesday, February 07, 2001 4:26 PM
> To: Multiple recipients of list ORACLE-L
> Hi -
> I am confused now about how oracle actually
> determines the size an extent
> should be.  I have db_block_size set at 8192 and
> have defined a tablespace
> (and tables) at initial and next extents of 128K.
> When I do a show
> parameter db_file_multiblock_read_count it says 8.
> Therefore I thought 128K
> would be a good number, since it is a multiple of
> these numbers.
> However, when I check my extent sizes, I see that
> each extent contains 10
> blocks which is 160K.
> I remember reading an article some time ago about
> how oracle actually
> determines what it thinks the extent size should be.
>  Does anyone know of an
> article like this, or can anyone explain to me why
> it chose a different
> extent size?
> By the way, I looked at several tables and the one
> common thing I noticed is
> that the number of blocks allocated seems to be a
> multiple of 5 - ie. some
> are 5 blocks, some 10, some 20, etc.  I don't know
> if that's coincidence or
> a big clue to the whole thing
> Lisa

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Author: Shakeel Qureshi
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