Determine the Number and Size of Extents
Storage parameters expressed in terms of extents define every segment. Storage
parameters apply to all types of segments. They control how Oracle allocates free
database space for a given segment. For example, you can determine how much space
is initially reserved for a table’s data segment or you can limit the number of extents
the table can allocate by specifying the storage parameters of a table in the STORAGE
clause of the CREATE TABLE statement. If you do not specify a table’s storage
parameters, then it uses the default storage parameters of the tablespace.
确定区块的数量和大小
存储参数的通过区块的条件来显示初始化每一个段。存储参数适合于段的所有类型。它们
控制ORACLE如何分配空间数据库空间对于一个给定的段。比如,你可以确定多少空间是
初始化预留给表的数据段或者你可以限定表可以分配的区块的数量通过指定的表的存储参数
在存储语句或者是创建表语句。如果你不指定表的存储参数,那么它将使用默认的表空间的
存储参数。
You can have dictionary managed tablespaces, which rely on data dictionary tables to
track space utilization, or locally managed tablespaces, which use bitmaps (instead of
data dictionary tables) to track used and free space. Because of the better performance
and easier manageability of locally managed tablespaces, the default for non-SYSTEM
permanent tablespaces is locally managed whenever the type of extent management is
not explicitly specified.
你可能拥有数据字典管理的表空间,它依赖于数据字典表去跟踪空间的使用,或者是本地
管理表空间,它使用们图(代替数据字典表)去跟踪使用和空闲空间。因为更好的性能和
更简单的管理对于本地管理的表空间,对于非系统永久表空间的默认表空间是本地管理的。
当一个区块的管理类型没有显式的指定时。
A tablespace that manages its extents locally can have either uniform extent sizes or
variable extent sizes that are determined automatically by the system. When you
create the tablespace, the UNIFORM or AUTOALLOCATE (system-managed) clause
specifies the type of allocation.
一个表空间本地管理它的区块可以使用区块大小单元或者是可变的区块大小,这些自动由
系统决定。当你创建表空间,那个UNIFORM或者AUTOALLOCATE(系统管理)语句指定了
分配的类型。
For uniform extents, you can specify an extent size or use the default size, which is
1 MB. Ensure that each extent contains at least five database blocks, given the
database block size. Temporary tablespaces that manage their extents locally can
only use this type of allocation.
对于区块的固定单元,你可以指定一个区块的大小或者使用默认值,它是1MB。确定那个
任何一个区块包含至少5个数据库块,给定数据块的大小。临时表空间本地的管理它们的区
块只能使用这种分配类型。
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