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如果查看Oracle数据块和操作系统块大小

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Jun 07, 2016 pm 03:50 PM

oracleOrdersizeoperating systemdataCheck

1、 1、在命令窗口中执行： SQL show parameter db_block_size NAME TYPE VALUE ------------------------------------ ----------------------------------------- db_block_size integer 8192 2、 2、在SQL窗口中执行： //查询实例的db_block_size（为81

1、 1、在命令窗口中执行：
SQL> show parameter db_block_size
NAME TYPE VALUE
------------------------------------ -----------------------------------------
db_block_size integer 8192

2、2、在SQL窗口中执行：
//查询实例的db_block_size值（为8192 bytes）
select value from v$parameter where name='db_block_size'
如果查看Oracle数据块和操作系统块大小

//查询出的回滚段中每个extent的初始分配的大小
select initial_extent fromdba_rollback_segs
如果查看Oracle数据块和操作系统块大小

//initial_extent值除以db_block_size后的结果：
select initial_extent/8192 fromdba_rollback_segs
如果查看Oracle数据块和操作系统块大小

由此可见，initial_extent值是db_block_size的整数倍，db_block_size的默认值为8192 bytes，是不能被用户修改的。因为db_block_size对应于一个实例，所以意味着在数据库创建（建库）以后是不能修改的，如需修改，可行的方式是重新建库并把原库的数据export到新库。当然最好的方式是在建数据库之前就规划好，一般如果是OLTP系统，可以保持默认值；OLAP环境可以考虑适当调大。

db_block_size典型的值有4096 bytes 和 8192 bytes，且必须是操作系统块（os block）的整数倍。操作系统块（os block）在Windows下可以通过fsutil工具查看，在Linux下则可以使用tune2fs命令。

Windows下使用方法如下：
D:\>fsutil fsinfontfsinfo c:
NTFS 卷序列号 :                      0x 388c89188c88d1b4
版本:                                        3.1
区数量:                                    0x00000000013fe599
簇总数:                                    0x000000000027fcb3
可用簇:                                    0x0000000000011e43
保留总数:                                 0x0000000000000060
每个扇区字节数:                      512
每个簇字节数:                          4096
每个FileRecord 段的字节数 :  1024
每个FileRecord 段的簇数 :

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