一. 官网说明

Logical Storage Structures

http://download.oracle.com/docs/cd/E11882_01/server.112/e16508/logical.htm#CNCPT7668

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其中有关ASSM 的内容如下：

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Logical Space Management

Oracle Database must use logical space management to track and allocate the extents in a tablespace. When a database object requires an extent, the database must have a method of finding and providing it. Similarly, when an object no longer requires an extent, the database must have a method of making the free extent available.

Oracle Database manages space within a tablespace based on the type that you create. You can create either of the following types of tablespaces:

·Locally managed tablespaces (default)

The database uses bitmaps in the tablespaces themselves to manage extents. Thus, locally managed tablespaces have a part of the tablespace set aside for a bitmap. Within a tablespace, the database can manage segments with automatic segment space management (ASSM)or manual segment space management (MSSM).

·Dictionary-managed tablespaces

The database uses the data dictionary to manage extents (see "Overview of the Data Dictionary").

Figure 12-3 shows the alternatives for logical space management in a tablespace.