Rollback segments and unlimited extents?

Could anyone comment on my recent TAR to oracle which is concerning whether
the 4096 maxextents makes any sense at all? Either I am not getting some basic
fact or I am correct in my assumption that 4096 is synonomous with unlimited in
some way and was done on purpose for the reasons below?

ORACLE:
If you are looking for the a way to calculate MAXEXTENTS for the default storage clause of the tablespace, then set it to UNLIMITED and not worry about it at all. There is no performance penalty in allowing an object to grow to a very large number of extents.

If you are looking for validation of the formula used, then the formula is has some problems.
1) It assumes that the file size provided will be in M, and the INITIAL will always be provided in K.
2) I am assuming that no rounding will take place when doing the division.
3) It ignores the fact that there is some amount of overhead that is required in the datafile header used for bookkeeping.

Also, If the storage clause if always specified for any objects created in the tablespace, then the default storage clause on the tablespace is never used.

MY RESPONSE:
New info : Thanks for that I will use unlimited for all my tablespaces except:
What about Rollback Segments
the docs specifically recomend not using unlimited. Again I submit your NOte: 117424.1 How to create an 8i DB in Unix page 4 has
create tablespace RBS DAtafile 'Filename' SIZE 12M reuse
MINIMUM EXTENT 128K
DEFAULT STORAGE ( INITIAL 128K NEXT 128K MINEXTENTS 2 MAXEXTENTS 4096 PCTINCREASE 0);
Rounding or other overhead aside I don't see how 4096 * 128 * 1024 < 12M ( my figure is 536.87 M ) Now I realize we probably won't use 4096 extents ( I believe we can never without adding data files ) but that is no reason to use the number if it is the same as unlimited. I would think of using maxextents < 90 ( probably 80 with your overhead comment )? Is the reason so
you can add datafiles and not have to modify maxextents? Does Oracle recomend using the storage clause with the create rollback segment
command rather than using the default storage clause? I have yet to see a
script that actually does that including NOTE:117424.1?

Thanks
Rob Received on Tue Oct 23 2001 - 10:39:51 CDT