Re: Datafile size - Is bigger better?

At 07:09 PM 11/14/2006, Wolfgang Breitling wrote:
>At 03:57 PM 11/14/2006, JayDBA wrote:
>>3. On locally managed files, we loose header space equal to the
>>extent size. E.g. on a datafile with uniform extent sizing of 128M
>>a 2gb file would waste 6% space / file. This number can run into
>>gigabytes on systems with 100's of 1000's of files
>
>That is not true. The bitmap(s) for managing the space are fixed at
>64K. If you create the datafiles for LMTs as an integral multiple of
>the uniform extent size + 64K, you can use the full size of the
>tablespace. If not Oracle will take the first extent and use 64K of
>it for the bitmap but the remainder is not usable - until you extent
>the datafile size by 64K:

I was describing that wrong. Oracle is not taking the first extent to create the space bitmap. It takes the first 64K of the datafile - after the file header block - to create the bitmap. The first extent then starts at an offset of 64K + 1 block. But if the datafile size does not include the extra 64K for the bitmap the space left after the last uniform size extent is allocated is 64K short of a full extent and is therefore unusable. Once the additional 64K are added, that unusable space plus the 64K make for a full uniform size extent and can be used.

Regards

Wolfgang Breitling
Centrex Consulting Corporation
www.centrexcc.com

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