| Lesson 12 | Creating additional rollback segments |
| Objective | Create user rollback segments for the COIN database. |
Creating Additional Rollback Segments
When you create a new database by using the CREATE DATABASE command, Oracle8 gives you a database with one rollback segment. This rollback segment sits in the SYSTEM tablespace and is not intended for general use.
Before you open the database for general use, you must create more rollback segments and you must place these in some other tablespace besides SYSTEM. In this case, you should place them in the RBS tablespace that you just created in the previous lesson.
The CREATE ROLLBACK SEGMENT command is used to create rollback segments. Move your mouse over the following diagram to learn about the syntax for this command.
The CREATE ROLLBACK SEGMENT command is used to create rollback segments. Move your mouse over the following diagram to learn about the syntax for this command.
- [PUBLIC]: An optional clause that only has meaning when you are running Parallel Server
- segment_name: The name of the rollback segment
- tablespace_name: The name of the tablespace where you want to store the rollback segment
- INITIAL integer: Specifies the size of initial extent to be allocated for the rollback segment
- NEXT integer: Specifies the size of any subsequent extents that are allocated to the rollback segment
- MINEXTENTS: Specifies the number of extents to initially allocate when the rollback segment is created. This must be at least two. Rollback segments must always have at least two extents.
- MAXEXTENTS: Specifies an upper limit on the number of extents that a rollback segment may have
- OPTIMAL: Tells Oracle8 the number of extents that you would prefer the rollback segment to have
Rollback Segments Syntax
The TABLESPACE and STORAGE clauses may be in any order, and all of the STORAGE parameters are optional. You need only specify the ones for which you do not want to use default values. You should always specify a tablespace though. Otherwise, the system tablespace is used by default. Placing a rollback segment in the system tablespace is considered bad form, and may have a negative impact on performance because of the extra I/O being added to an already heavily used tablespace. Click the Exercise link below to practice what you have learned. In this exercise, you will write some CREATE ROLLBACK SEGMENT commands for your COIN database.