Specifying Storage Parameters for Rollback Segments

• Setting Storage Parameters When Creating a Rollback Segment

• Changing Rollback Segment Storage Parameters

• Altering Rollback Segment Format

• Shrinking a Rollback Segment Manually

Setting Storage Parameters When Creating a Rollback Segment

• The rollback segment is allocated an initial extent of 50K.

• The rollback segment is allocated the second extent of 50K.

• The optimal size of the rollback segment is 750K.

• The minimum number of extents and the number of extents initially allocated when the segment is created is 15.

• The maximum number of extents that the rollback segment can allocate, including the initial extent, is 100.

CREATE PUBLIC ROLLBACK SEGMENT data1_rs

   TABLESPACE users

   STORAGE (

      INITIAL 50K

      NEXT 50K

      OPTIMAL 750K

      MINEXTENTS 15

      MAXEXTENTS 100);

You can also use the Create Rollback Segment property sheet of Server Manager to set the rollback segment's storage parameters.

Changing Rollback Segment Storage Parameters

Alter a rollback segment's storage parameters using either the Alter Rollback Segment property sheet of Server Manager, or the SQL command ALTER ROLLBACK SEGMENT.

The following statement alters the maximum number of extents that the DATA1_RS rollback segment can allocate.

ALTER PUBLIC ROLLBACK SEGMENT data1_rs 
   STORAGE (MAXEXTENTS 120);

You can alter the settings for the SYSTEM rollback segment, including the OPTIMAL parameter, just as you can alter those of any rollback segment.

Note: If you are altering a public rollback segment, you must include the keyword PUBLIC in the ALTER ROLLBACK SEGMENT command.

See Also: For guidance on setting sizes and storage parameters (including OPTIMAL) for rollback segments, see "Guidelines for Managing Rollback segments" .

Altering Rollback Segment Format

You can define limited or unlimited format for rollback segments. When converting to limited or unlimited format, you must take the rollback segments offline. If you identify unlimited format for rollback segments, extents for that segment must have a minimum of 4 data blocks. Thus, a limited format rollback segment cannot be converted to unlimited format if it has less than 4 data blocks in any extent. If you want to convert from limited to unlimited format and have less than 4 data blocks in an extent, your only choice is to drop and re-create the rollback segment.

Shrinking a Rollback Segment Manually

You can manually decrease the size of a rollback segment using the SQL command ALTER ROLLBACK SEGMENT. The rollback segment you are trying shrink must be online.

The following statement shrinks rollback segment RBS1 to 100K:

ALTER ROLLBACK SEGMENT rbs1 SHRINK TO 100K;

See Also: For a complete description of the ALTER ROLLBACK SEGMENT command, see the Oracle7 Server SQL Reference.