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----- Original Message -----
To: "Multiple recipients of list ORACLE-L" <[EMAIL PROTECTED]>
Sent: Friday, September 14, 2001 7:45 AM
> !! Please do not post Off Topic to this List !!
>
>
> Don,
>
> Just to confirm a point that I think that you are making:
>
> Each tablespace should only have one extent size in it?
Yes, in any given tablespace there is ONLY one extent size. Initial = next for
everything and every (initial extent size) = (every other initial extent size) -
for everything in the tablespace. (Except for SYSTEM).
> Once you get too many extents, you move the object up to the next-size
> tablespace?
If you must. Better in my opinion is to size for growth. For example, if you
have a table that is currently 200M, but it will grow to 20G in two years,
prefer initially putting it into a tablespace appropriate for a 20 GB table.
The percentage of "wasted space" will be fairly high initially, but will
decrease as it grows - and you won't have to move it later.
Consider that, on average, one half of one extent will be as yet unused -
"wasted". As the number of extents grows, that fixed amount of space gets to be
a smaller percentage of the total. For example, a uniform extent policy:
A table consists of N extents
Each and every extent is of size M
Average "wasted space" = M/2
(If anyone wants to extend this line of reasoning for parallel loads, etc. -
feel free!)
Total space in N extents = N*M
The ratio of wasted space to total space is (M/2)/(N*M) = M/[2(M*N)] = 1/(2N)
{Sanity check!: 4 extents, 0.5 extent unused -> 1/8 of space is "wasted".
1/(2*4) = 1/8. It checks.}
To convert to a percentage, multiply by 100.
=> Average percentage of total space for table extents that is "wasted space" W
= 100*[1/(2N)] = 50/N
As the value of N (the number of extents) increases, the value of W (the
percentage of wasted space) decreases.
[Note: This, of course, does not consider free space within blocks, ILT space,
and all the other geeky Oracle stuff - nor should it. All that will be present
whether you have one extent or a thousand. It is a separate issue entirely.]
> Thanks,
>
> Cherie
You are quite welcome!
-Don Granaman
[OraSaurus - Honk if you remember UFI!]
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Author: Don Granaman
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