Database Logical & Physical Architecture 3

74. How does Space allocation table place within a block?
Each block contains entries as follows
Fixed block header
Variable block header
Row Header, row date (multiple rows may exists)
PCTEREE (% of free space for row updating in future)

75. What is the role of PCTFREE parameter is storage clause?
This is used to reserve certain amount of space in a block for expansion of rows.

76. What is the OPTIMAL parameter?
It is used to set the optimal length of a rollback segment.

77. What is the functionality of SYSTEM table space?
To manage the database level transactions such as modifications of the data dictionary table that record information about the free space usage.

78. How will you create multiple rollback segments in a database?
- Create a database, which implicitly creates a SYSTEM rollback segment in a SYSTEM tablespace.
- Create a second rollback segment name R0 in the SYSTEM tablespace.
- Make new rollback segment available (after shutdown, modify init.ora file and start database)
- Create other tablespaces (RBS) for rollback segments.
- Deactivate rollback segment R0 and activate the newly created rollback segments.