控制文件oracle controlfile structure

可以看到件组总计为7007244bytes

可以看出控制文件块是数据文件块的2倍巨细，是实其控制文件块用两个同相的块成组了一个逻辑块

这里还要注意到并非全部件组会都有镜像，所以控制文件的巨细并非件组所占间空的2倍巨细

看一下精确法算：

控制文件含包的内容：

控制文件出了块级的镜像，还有文件级的镜像，所以每一个控制文件时一样的

参阅：http://www.ixora.com.au/notes/controlfile_structure.htm

The first block of the controlfile is a header block that records just the controlfile block size and the number of blocks in the controlfile. The controlfile block size is the same as the database block size. When mounting a database, Oracle checks that the controlfile block size and the file size recorded in the controlfile header block match the   db_block_size  parameter and the file size reported by the operating system (if available). Otherwise an error is raised to indicate that the controlfile might have been corrupted or truncated.

After the header block, all controlfile blocks occur in pairs. Each logical block is represented by two physical blocks. This is necessary for the controlfile transaction mechanism.

It is theoretically possible that a hot backup of a controlfile could contain a split block. Therefore all controlfile blocks other than the file header have a cache header and tail that can be compared when mounting a database and whenever a controlfile block is read. The block type is 0 for virgin controlfile blocks and 21 otherwise. The physical controlfile block number is used in place of an RDBA in the cache header, and a controlfile sequence number is used in place of an SCN to record when the block was last changed. An ORA-00227 error is returned if the header and tail do not match, or if the block checksum does not match the checksum recorded in the cache header (if any).

The controlfile contains several different types of records, each in its own record section of one or more logical blocks. Records may span block boundaries within their section. The fixed view V$CONTROLFILE_RECORD_SECTION lists the types of records stored in each record section, together with the size of the record type, and the number of record slots available and in use within that section. The underlying X$KCCRS structure includes the starting logical block number (RSLBN) for each section.