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Re: extent management LOCAL size uniform 1M takes 1M space NOT 64K

From: Madhavan Amruthur <>
Date: Mon, 17 Jul 2000 08:46:58 PDT
Message-Id: <>

Hi Rahul,
If you need a 500M tablespace and u need 500 1M extents then the datafile must be 500*1024 = 512000K + 64K = 512064K. The 64K is used for the bitmap that manages the space allocation and deallocation for LMT.

If you do not add that 64K then it basically grabs one extent as though it needs only 64K, since there is a uniform extent size, it grabs one extent and if you chekc dba_data_files there are 2 columns called bytes and user_bytes. Bytes is the total allocated and user_bytes is the space u have. So in this case u would have seen 500M in bytes column and 499M is user bytes column. If you create the datafile as above, then you would see the correct values.

Also if you have extents that are not divisible by the size then also you would have wasted space. For eg: if datafile size is 512064 K and you have 3M extents then 500/3 = 166.67 which means you will get 166 extents and the 2M is wasted and cannot be used. ie 166*3 = 498 and the extra 2M is not used.

Hope this helps.

IBM Corporation

>From: Rahul <>
>To: Multiple recipients of list ORACLE-L <>
>Subject: extent management LOCAL size uniform 1M takes 1M space NOT 64K
>Date: Mon, 17 Jul 2000 04:16:32 -0800
>List, a while ago there was a thread regarding locally manage tablespaces
>and in the end we agreed that it takes 64K space for the bitmap in the
>locally managed tablespace...
>i just created my first locally managed tbs of 500M and i got only 499 MB
>create tablespace DATA_UNI_1M
>datafile '/hd1/oradata/SASS/DataUni1M/datauni1m01.dbf' size 500m
>extent management local uniform size 1M;
>select BYTES from dba_free_space where TABLESPACE_NAME ='DATA_UNI_1M';
>499 MB !!
>Author: Rahul
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