Quick follow up to the bitmap sizing for
larger files: I've quoted this 20-30,000
figure in my book as applying to both
'ordinary' LMTs and 'temporary' LMTs.
However following our discussions, and
a conversation with Ken Robinson from
Oracle, I've run a couple of tests on 8.1.7
and the 2-bytes per extent that led to
me quoting these figures applies only
to temporary LMTs.
In an ordinary LMT, one bit equates
to one extent, so for an 8K block size,
which gives you 6 blocks (64K - 2 blocks)
in the first bitmap you could build ca. 380,000
extents in a single file before adding more bitmap
at the end; for a very small file with its special
one-block bitmap, you could still at about 63,500
extents without a new chunk of bitmap appearing.
Jonathan Lewis
Seminars on getting the best out of Oracle
Last few places available for Sept 10th/11th
See http://www.jlcomp.demon.co.uk/seminar.html
| Earlier experiments indicated that for very
| large files, with small extents, so that the
| total extent count exceeded about 20,000 -
| 30,000 (related to block size and therefore
| number of blocks actually available from the
| 64K for bitmap) - an extra 64K space would
| be pre-allocated at the head of file. I did not
| test for further extremes - if you have small
| extents you should not have very large files.
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