Name

CREATE ROLLBACK SEGMENT

Synopsis

CREATE [PUBLIC] ROLLBACK SEGMENT
segment_name
   TABLESPACE tablespace_name
   [STORAGE (
      [INITIAL integer[K | M] ]
      [NEXT integer[K | M] ]
      [MINEXTENTS integer[K | M] ]
      [MAXEXTENTS {integer | UNLIMITED} ]
      [PCTINCREASE integer]
      [FREELISTS integer]
      [FREELIST GROUPS integer] ]
      [OPTIMAL {integer[K | M] | NULL} ]
   ) ]

Creates a rollback segment (segment_name), which is used by Oracle to store data necessary to roll back changes made by transactions.

Keywords

PUBLIC

Specifies that this rollback segment is available to any instance. If PUBLIC is omitted, it is only available to the instance naming it in the ROLLBACK_SEGMENTS parameter in the INIT.ORA file.

TABLESPACE

Specifies the tablespace (tablespace_name) where this rollback segment will be created.

STORAGE

Specifies the physical characteristics of the rollback segment as follows:

INITIAL

Specifies the size of the first extent for this rollback segment in bytes, kilobytes, or megabytes. If this value is not a multiple of the database blocksize, it will be rounded up to a multiple of the database blocksize.

NEXT

Specifies the size of the next extent in bytes, kilobytes, or megabytes. If this value is not a multiple of the database blocksize, it will be rounded up to a multiple the of database blocksize.

MINEXTENTS

Specifies the number of extents to be allocated when this rollback segment is created. The minimum number of extents for a rollback segment is 2, and this is the default.

MAXEXTENTS

Specifies the maximum number of extents that may be allocated for this rollback segment. The default will vary according to the database blocksize. Specify UNLIMITED for unlimited expansion.

PCTINCREASE

Specifies the percentage by which each extent will grow over the previous extent. The default is 50, which means that each extent will be one-and-one-half times larger than the previous extent. It is recommended that rollback segments use a PCTINCREASE value of 0, in order to allocate equal-size extents.

FREELISTS

Specifies the number of free lists contained in each freelist group in this rollback segment. The default is 1, and the maximum depends on the database blocksize.

FREELIST GROUPS

Specifies the number of groups of free lists for this rollback segment. The default is 1. This parameter should be used only with the Parallel Server option running in parallel mode.

OPTIMAL

Specifies the optimal size for this rollback segment. Oracle will attempt to maintain this size by deallocating unused extents. The default is NULL, which means that no deallocation will ever take place.

Notes

You must have the CREATE ROLLBACK SEGMENT privilege to issue this command. The tablespace must be online for you to create a rollback segment in it. When it is created, the rollback segment will be offline and must be brought online by using the ALTER ROLLBACK SEGMENT statement or restarting the database with the rollback segment named in the INIT.ORA file.

Example

The following example creates a rollback segment rbs02:

CREATE ROLLBACK SEGMENT rbs02
   TABLESPACE rollback
   STORAGE (INITIAL 40K NEXT 40K PCTINCREASE 0)
..................Content has been hidden....................

You can't read the all page of ebook, please click here login for view all page.
Reset