Database Logical & Physical Architecture 4

79. How the space utilization takes place within rollback segments?
It will try to fit the transaction in a cyclic fashion to all existing extents. Once it found an extent is in use then it forced to acquire a new extent (number of extents is based on the optimal size)

80. Why query fails sometimes?
Rollback segment dynamically extent to handle larger transactions entry loads.
A single transaction may wipeout all available free space in the rollback segment tablespace. This prevents other user using rollback segments.

81. How will you monitor the space allocation?
By querying DBA_SEGMENT table/view

82. How will you monitor rollback segment status?
Querying the DBA_ROLLBACK_SEGS view

IN USE - Rollback Segment is on-line.
AVAILABLE - Rollback Segment available but not on-line.
OFF-LINE - Rollback Segment off-line
INVALID - Rollback Segment Dropped.
NEEDS RECOVERY - Contains data but need recovery or corrupted.
PARTLY AVAILABLE - Contains data from an unresolved transaction involving a
distributed database.

83. List the sequence of events when a large transaction that exceeds beyond its optimal value when an entry wraps and causes the rollback segment to expand into another extend.
Transaction Begins.
An entry is made in the RES header for new transactions entry
Transaction acquires blocks in an extent of RBS
The entry attempts to wrap into second extent. None is available, so that the RBS must extent.
The RBS checks to see if it is part of its OPTIMAL size.
RBS chooses its oldest inactive segment.
Oldest inactive segment is eliminated.
RBS extents
The data dictionary tables for space management are updated.
Transaction Completes.