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Bringing Tablespaces Offline (55)

原创 IT综合 作者:tsinglee 时间:2007-10-10 17:27:25 0 删除 编辑

When a tablespace goes offline, Oracle does not permit any subsequent SQL
statements to reference objects contained in that tablespace. Active transactions with
completed statements that refer to data in that tablespace are not affected at the
transaction level. Oracle saves rollback data corresponding to those completed
statements in a deferred rollback segment in the SYSTEM tablespace. When the
tablespace is brought back online, Oracle applies the rollback data to the tablespace, if
needed.
When a tablespace goes offline or comes back online, this is recorded in the data
dictionary in the SYSTEM tablespace. If a tablespace is offline when you shut down a
database, the tablespace remains offline when the database is subsequently mounted
and reopened.
You can bring a tablespace online only in the database in which it was created because
the necessary data dictionary information is maintained in the SYSTEM tablespace of
that database. An offline tablespace cannot be read or edited by any utility other than
Oracle. Thus, offline tablespaces cannot be transposed to other databases.
Oracle automatically switches a tablespace from online to offline when certain errors
are encountered. For example, Oracle switches a tablespace from online to offline
when the database writer process, DBWn, fails in several attempts to write to a datafile
of the tablespace. Users trying to access tables in the offline tablespace receive an error.
If the problem that causes this disk I/O to fail is media failure, you must recover the
tablespace after you correct the problem.

1. 但表空间脱机时 , 引用了该表空间中的对象的SQL都不允许被执行 , Oracle将回滚信息保存在system表空间deferred rollback segment
2. 关闭数据库时间 , 如果表空间是脱机的 , 那么当数据库重新打开或者被加载的时候 , 该表空间仍然是脱机的

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