rollback_segments

[elintrend]

Hi all,

I just noticed that no rollback_segment specified in my ini.ora file. Does that mean next time when db startup, all rollback_segment won't be online (execept system rbs)?
I have startup DB several times already, and everytime rbs are all online. - confused now.

thanks in advance

[rsuri]

if the rollback segments are PUBLIC then they will come online. Only for PRIVATE rollbacks you need to list them in the init file.

- Rajeev

[Kishore]

When the RBS are created as default like now in 8 version RBS01 .. RBS20 are created by default, and if you are using the same, then you dont have to specify in your INIT.ora .

Probably that's what is happening.

[jmodic]

If you don't have any rollback segs specified in your init.ora, Oracle will calculate the number of RB segments it needs based on the following formula: number_of_RB_to_put_online = TRANSACTIONS/
TRANSACTIONS_PER_ROLLBACK_SEGMENT. If you have this number of RB segments created it will bring all online. If you have more than this number of RB segments it will left the others in offline mode.

[jmodic]

Originally posted by rsuri
if the rollback segments are PUBLIC then they will come online. Only for PRIVATE rollbacks you need to list them in the init file.

AFAIK public and private RB segments are relevant only in Paralel Server environment. In normal configuration they behave exactly the same and the type of RB segment does not have any influence in the decision if system will bring the RB online or not.

[elintrend]

When rollblck_segments rbs_01 created,

CREATE ROLLBACK SEGMENT rbs_01
TABLESPACE
STORAGE (INITIAL 10k NEXT 10k MINEXTENTS 2);

how to make it public or priv. during creation of rbs

20 rbs of my are public- if I don't specific when creating them, they are public. and acoording the formula, some will be online automatically. CORRECT!

[sree_sri]

I am not sure about the formula, But when you are creating the rollback segments you have to specify the PUBLIC in
create syntax,

Other whys the rollback segment will be created as private.
(On my knowledge).

[vijay8282]

Hi Jmodic,

You are saying that :

If you don't have any rollback segs specified in your init.ora, Oracle will calculate the number of RB segments it needs based on the following formula: number_of_RB_to_put_online = TRANSACTIONS/
TRANSACTIONS_PER_ROLLBACK_SEGMENT

From where Oracle is going to get both the parameters.

Pls. elaborate.

[jmodic]

Those are initialisation parameters. You might have them specified in the initSID.ora. If you don't specify them there oracle will assign some default values to them during startup. To check what values have been assigned to them in your instance, run the following:

SELECT name, value FROM v$parameter
WHERE UPPER(name) IN ('TRANSACTIONS', 'TRANSACTIONS_PER_ROLLBACK_SEGMENT');

HTH,

[padmam]

Dear Jmodic, 10th May 2001 16:34 hrs chennai

As you have said fine i queried the v$parameter it shows as follows.

NAME VALUE
---------------------------------------------------------------- ------
transactions 75
transactions_per_rollback_segment 5

So i should have 15 RBS ? but my query reads as follows

SQL> select * from v$rollname;

USN NAME
---------- ---------------------
0 SYSTEM
1 RBS0
2 RBS1
3 RBS2
4 RBS3
5 RBS4
6 RBS5
7 RBS6

Note :In My init.ora RBS related parameters has been disabled.

# If using private rollback segments, place lines of the following
# form in each of your instance-specific init.ora files:
#rollback_segments = ( RBS0, RBS1, RBS2, RBS3, RBS4, RBS5, RBS6 )

# If using public rollback segments, define how many
# rollback segments each instance will pick up, using the formula
# # of rollback segments = transactions / transactions_per_rollback_segment
# In this example each instance will grab 40/5 = 8
# transactions = 40
# transactions_per_rollback_segment = 5

Cheers

Padmam