英文太烂
一，段的简介

A segment is a set of extents that contains all the data for a specific logical storage structure within a tablespace. For example, for each table, Oracle allocates one or more extents to form that table's data segment, and for each index, Oracle allocates one or more extents to form its index segment.

在表空间中，段是一组包涵所有的数据的区组成，是指定的逻辑存储结构。举例来说，每个表中，oracle从表所在的数据段分配一个或者多个区给它，对于每个索引来说，oracle从索引所在的索引段分配一个或者多个区给它

二，段与对象的关系
Data segment Each nonclustered table has a data segment. All table data is stored in the extents of the data segment.
数据段，每个普通表都有一个数据段，所有表的数据存储在数据段的区里。

For a partitioned table, each partition has a data segment.
对于一个分区表来说，每个分区都有一个partition segment

Each cluster has a data segment. The data of every table in the cluster is stored in the cluster's data segment.
每个簇都有一个数据段，在簇里的每个表的数据都存储在粗的数据段里

Index segment Each index has an index segment that stores all of its data.
索引段，每个索引都有一个索引段来存储索引的数据

For a partitioned index, each partition has an index segment.
对于一个分区索引，每个分区都有一个索引段

Temporary segment Temporary segments are created by Oracle when a SQL statement needs a temporary database area to complete execution. When the statement finishes execution, the extents in the temporary segment are returned to the system for future use.
临时段，当一条sql语句需要临时的数据库空间来执行时，临时段会被oracle创建。当sql语句执行完毕时，在临时段中的区将被回收以便将来使用。

Rollback segment If you are operating in automatic undo management mode, then the database server manages undo space using tablespaces. Oracle recommends that you use automatic undo management.
回滚段，当你系统处于自动undo管理模式时，那么数据库服务管理undo空间使用表空间。oracle推荐你使用undo自动管理模式。

三，单独的数据段

A single data segment in an Oracle database holds all of the data for one of the following:
以下是在oracle数据库中，一个单独的数据段存储所有的数据

A table that is not partitioned or clustered
非簇表和非分区表
A partition of a partitioned table
分区表里的其中一个分区
A cluster of tables
一个簇

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segment的理解

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