As long as a nonclustered table exists or until you truncate the table, any data block
allocated to its data segment remains allocated for the table. Oracle inserts new rows
into a block if there is enough room. Even if you delete all rows of a table, Oracle does
not reclaim the data blocks for use by other objects in the tablespace.
After you drop a nonclustered table, this space can be reclaimed when other extents
require free space. Oracle reclaims all the extents of the table’s data and index
segments for the tablespaces that they were in and makes the extents available for
other schema objects in the same tablespace.
In dictionary managed tablespaces, when a segment requires an extent larger than the
available extents, Oracle identifies and combines contiguous reclaimed extents to form
a larger one. This is called coalescing extents. Coalescing extents is not necessary in
locally managed tablespaces, because all contiguous free space is available for
allocation to a new extent regardless of whether it was reclaimed from one or more
extents.

1. delete不回收extents , drop回收extents
2. dmt,当请求的extent大于可用的extent时,Oracle将识别和合并相邻的extents , 叫做coalescing extents
3. lmt,可以不继续关注coalescing extents

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Extents in Nonclustered Tables(16)

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