Re: Datafile size - Is bigger better?
- From: Wolfgang Breitling <breitliw@xxxxxxxxxxxxx>
- To: jaykash@xxxxxxxxxxx
- Date: Tue, 14 Nov 2006 21:40:03 -0700
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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