Which of the following statements accurately describes the chaining and migration of Oracle blocks? (Choose two.)
A. Chaining occurs when a row is too large to fit into a single data block.
B . Chaining occurs when a row is updated and will not fit back into the block where its physical ROWID points to.
C . Migration occurs when a row is too large to fit into a single data block.
D. Migration occurs when a row is updated and will no longer fit back into the block where its physical ROWID points to, but will fit into another data block.
E . The physical ROWID changes to the new block in both chaining and migration.
Explanation:
Answer A and D: Chaining and migration are two distinctly different events that can occur to rows of data in a data block. An INSERT or UPDATE can cause chaining usually if the row is very large. Migration occurs when a row is updated, and the row will not fit back into the block. If Oracle finds enough free space and has to move the row to another block, a small piece of the row remains in the original block, so the ROWID doesn't change. Neither row chaining nor migration requires index rebuilds.
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