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Re: locally managed autoallocate (was: Separate Indexes and

From: Wolfgang Breitling <>
Date: Tue, 30 Sep 2003 20:59:28 -0800
Message-ID: <>

I can't recall right now where I found out about the 3 blocks required for automatic space management. Could have been an error message when I tried to create a table with a 2 block extent in an ASSM tablespace, or a presentation at IOUG, or perhaps even on this list. The 5 block rule is the documented allocation rule for DMT where Oracle rounds requests for segments greater than 5 blocks to the next multiple of 5 blocks (unless it finds a free segment of exactly the right size or ...). Which is why you couldn't implement a uniform extent size policy in DMT with extent sizes of exact powers of 2 (64, 128, 256, 1024, ...) to make use of the full IO bandwith of the OS (which is generally a power of 2) for full scans since they all were not multiples of 5 blocks. Not until the minimum extent size option came in Oracle 8 (not to be confused with minextents). But then LMTs came in Oracle 8i and retired the entire DMT allocation scheme.

At 07:49 PM 9/30/2003 -0800, you wrote:

>I repeated your test, with the same result. You, of course, are right.
>Interesting, that means that oracle gave up on that "5 blocks rule".
>Where did you come accross the fact that automatic space management
>requires 3 blocks? That is, I suppose, for freeelists & freelist groups?
>I must confess that I assumed that the old 5 blocks rule still holds true,
>so I didn't test further. Also, I was testing the problem that I had with
>autoallocate and automatic segment management, which turned out to be
>a SCSI controller problem. Basically, when I created the tablespace on EIDE
>device, it worked as advertised, but when I attempted to do that on a SCSI
>disk, it failed. To dispell all doubts, SCSI controller died in 2 days,
>causing, of course a system and the database crash. May it rest in peace,
>in the place SCSI controllers go when they burn out.
>Mladen Gogala
>Oracle DBA
>Please see the official ORACLE-L FAQ:
>Author: Mladen Gogala

Wolfgang Breitling
Oracle7, 8, 8i, 9i OCP DBA
Centrex Consulting Corporation

Please see the official ORACLE-L FAQ:
Author: Wolfgang Breitling

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Received on Tue Sep 30 2003 - 23:59:28 CDT

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