数据文件头块保留大小、ROWID、数据文件最大大小等数据库限制的
学习自EYGLE循序渐进ORACLE及官方文档。 本地管理表空间中设置不同大小的db_block_size时数据文件头保留空间对应如下： db_block_size=2KB，文件头保留32个数据块，即64KB。 db_block_size=4KB，文件头保留16个数据块，即64KB。 db_block_size=8KB，文件头保
学习自EYGLE循序渐进ORACLE及官方文档。本地管理表空间中设置不同大小的db_block_size时数据文件头保留空间对应如下：
db_block_size=2KB，文件头保留32个数据块，即64KB。db_block_size=4KB，文件头保留16个数据块，即64KB。
db_block_size=8KB，文件头保留8个数据块，即64KB。
db_block_size=16KB，文件头保留4个数据块，即64KB。
db_block_size=32KB，文件头保留4个数据块，即128KB。
默认是db_block_size=8KB，此时 ORACLE数据文件头的8个数据块作用是：
数据块1和2记录数据文件头信息。3-8用于记录extent-区间的位图信息 --11G中要保留到128个块？？？
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Oracle数据库中的数据文件的最大数量是有限的（通常为64K文件）。--来自官方文档
表空间支持的最大数据文件大小的算法：
分两种情况：smallfile tablespace与bigfile tablespacesmallfile tablespace的ROWID
记录存储所在数据文件(file#),所属数据库对象，所在数据块中的行号，这些属性合并起来构成了ORACLE ROWID.ORACLE ROWID分为物理ROWID，逻辑ROWID。
索引组织表（IOTs)使用逻辑ROWID,其它类型的表使用物理ROWID。
ROWID可以惟一标识一条记录，所以索引中存储了ROWID的值，通过访问索引，得到ROWID,再定位到记录。
ROWID采用Base64编码，共18位代表80位二进制数，占用10个字节。
每组字符代表不同的含义，18位最大寻址空间“32G”。。
对一条行ID的解析：OOOOOO.FFF.BBBBBB.RRR --其中.是为了方便观看手动增加
OOOOOO： 1-6位：对象id
FFF： 7-9位：文件id
BBBBBB： 10-15位：块id
RRR： 16-18位：行id
对于Base64编码，共18位代表80位二进制数，计算方法是：
32bit obj# + 10bit file# + 22bit block# + 16bit row#
通过ROWID计算数据块的相关信息，详见：http://blog.csdn.net/q947817003/article/details/11490051
根据small file tablespace的ROWID，计算出表空间、数据文件、BOOCK中行最大数如下：
根据ROWID的构成: ---注：2^10这种写法代表2的10次方，等于1024.
每个表空间最大文件数： 2^10 1024 ，去掉全0和全1 通常1022个 ---实验测试出是1023个，见：数据文件个数大于1024时ORACLE数据文件FILE_ID及RELATIVE_FNO的变化示例
每数据文件最大数据块数量：filesize=block_size*2^22 ，也就是4M个ORACLE BLOCK
每个BLOKC中行数是： 2^16 65536，也就是每个BLOCK最多65536条记录
每个数据库最多65536个-64K个数据文件（实验测试出是65534----官方文档上是65533-http://docs.oracle.com/cd/B19306_01/server.102/b14237/limits002.htm#i287915），最多支持64K个表空间，因为每个表空间最少需要包含一个数据文件。引出新问题：如果数据库有大于1024个数据文件，ORACLE如何通过ROWID定位数据文件呢？
--详见：数据文件个数大于1024时ORACLE数据文件FILE_ID及RELATIVE_FNO的变化示例
smallfile tablespace设置不同大小的db_block_size时数据文件允许的最大大小
db_block_size=2KB，2KB*4M=8192M 8Gdb_block_size=4KB，4KB*4M=16384M 16G
db_block_size=8KB，8KB*4M=32768M 32G 8*1024*4M=8*4G=32G
db_block_size=16KB，16KB*4M=65536M 64G
db_block_size=32KB，32KB*4M=131072M 128G
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BIGFILE表空间的ROWID
因为大文件表空间只能包含一个文件，所以ROWID中不需要file#-文件ID。大文件表空间的ROWID格式为：
OOOOOO.LLLLLLLLL.RRR
OOOOOO： 1-6位：对象id
LLLLLLLLL： 7-15位：块id
RRR： 16-18位：行id
L代表BLOCK号，代替了小文件表空间中ROWID中的file# + block#的位置.
这样大文件表空间的数据文件支持的BLOCK数量最多是：2bit. 2^32=4G.
bigfile tablespace设置不同大小的db_block_size时数据文件允许的最大大小
db_block_size=2KB，2KB*4G= 8Tdb_block_size=4KB，4KB*4G= 16T
db_block_size=8KB，8KB*4G= 32T 8*1024*4G=8*4TB=32TB
db_block_size=16KB，16KB*4G= 64T
db_block_size=32KB，32KB*4G=128TB
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