Identify two situations in which the block header grows in a data block. (Choose two.)
A.
When row directories need more row entries
B.
When there is row migration in the data block
C.
When there is an increase in the PCTFREE value for the data block
D.
When more transaction slots are required than are initially configured
Explanation:
Database Block: Contents
Block header: The block header contains the segment type (such as table or index), data block
address, table directory, row directory, and transaction slots of size 24 bytes each, which are used
when modifications are made to rows in the block. The block header grows downward from the
top.
Row data: This is the actual data for the rows in the block. Row data space grows upward from
the bottom.
Free space: Free space is in the middle of the block, enabling the header and the row data
space to grow when necessary. Row data takes up free space as new rows are inserted or as
columns of existing rows are updated with larger values.
Examples of events that cause header growth:
– Row directories that need more row entries
– More transaction slots required than initially configured
Initially, the free space in a block is contiguous. However, deletions and updates may fragment the
free space in the block. The free space in the block is coalesced by the Oracle server when
necessary.
