When you create a table, Oracle automatically allocates a data segment in a tablespace
to hold the table’s future data. You can control the allocation and use of space for a
table’s data segment in the following ways:
■ You can control the amount of space allocated to the data segment by setting the
storage parameters for the data segment.
■ You can control the use of the free space in the data blocks that constitute the data
segment’s extents by setting the PCTFREE and PCTUSED parameters for the data
segment.
Oracle stores data for a clustered table in the data segment created for the cluster
instead of in a data segment in a tablespace. Storage parameters cannot be specified
when a clustered table is created or altered. The storage parameters set for the cluster
always control the storage of all tables in the cluster.
A table’s data segment (or cluster data segment, when dealing with a clustered table)
is created in either the table owner’s default tablespace or in a tablespace specifically
named in the CREATE TABLE statement.

数据是怎么存储的
1. 当用户创建一个表时,Oracle 会自动地在相应的表空间内为此表分配数据段来保存数据
2. 用户可以采用以下方式分别控制数据段的空间分配与使用：
a. 通过设定数据段的存储参数来控制空间分配总数
b. 通过设定数据段的 PCTFREE 和 PCTUSED 参数,来控制如何使用数据块中的可用空间.

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