Which two statements are true about extents?

A. Blocks belonging to an extent can be spread across multiple data files.
B. Data blocks in an extent are logically contiguous but can be non-contiguous on disk.
C. The blocks of a newly allocated extent, although free, may have been used before.
D. Data blocks in an extent are automatically reclaimed for use by other objects in a tablespace when all the rows in a table are deleted.

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Answer:

The correct answers are B and C.

In an Oracle Database, extents are a way of allocating and managing data space. Blocks belonging to an extent can be spread across multiple data files, but data blocks within an extent are logically contiguous even if they are not physically contiguous on disk. When a new extent is allocated, the blocks may have been used before, but they are marked as free. Lastly, when all the rows in a table are deleted, the data blocks in the extent are automatically reclaimed for use by other objects in the tablespace.

Statement B is true because data blocks within an extent are logically contiguous, meaning they're grouped together in a specific order. However, on disk, these blocks may not be physically contiguous - they could be spread out in different locations on the disk.

Statement C is also true because a newly allocated extent may contain blocks that were previously used by other objects in the tablespace. These blocks are marked as free but may still contain data from their previous use.

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