我以前介绍过获得redo block size的方法，当然也可以通过dbfsize工具获得。
现在在这里我想介绍的是另外一种非典型方法，有多非典型呢?
问题来自于N年前我在一个客户的机器上部署的监控脚本，现在那些脚本看来还在运行着，我最近收到了大量类似如下内容的邮件:
ORA-16038: log 2 sequence# 17151 cannot be archived
ORA-19504: failed to create file ""
ORA-00312: online log 2 thread 1: '/eXPort/home/Oracle/oradata/cuwap/redo02.log'
ORA-19504: failed to create file "/data1/oraarc/PTL017151.arc"
ORA-19504: failed to create file "/data1/oraarc/PTL017151.arc"
ORA-27044: unable to write the header block of file
ORA-16038: log 2 sequence# 17151 cannot be archived
ORA-19504: failed to create file ""
ORA-00312: online log 2 thread 1: '/export/home/oracle/oradata/cuwap/redo02.log'
ORA-19504: failed to create file "/data1/oraarc/PTL017151.arc"
ORA-19504: failed to create file "/data1/oraarc/PTL017151.arc"
ORA-27044: unable to write the header block of file
ORA-16038: log 2 sequence# 17151 cannot be archived
ORA-19504: failed to create file ""
ORA-00312: online log 2 thread 1: '/export/home/oracle/oradata/cuwap/redo02.log'
ORA-19502: write error on file "/data1/oraarc/PTL017151.arc", blockno 169985 (blocksize=512)
ORA-27072: skgfdisp: I/O error
ORA-19502: write error on file "/data1/oraarc/PTL017151.arc", blockno 169985 (blocksize=512)
ORA-19502: write error on file "/data1/oraarc/PTL017152.arc", blockno 57345 (blocksize=512)
ORA-27072: skgfdisp: I/O error
ORA-19502: write error on file "/data1/oraarc/PTL017152.arc", blockno 57345 (blocksize=512)
ORA-16038: log 2 sequence# 17151 cannot be archived
ORA-19502: write error on file "", blockno (blocksize=)
ORA-00312: online log 2 thread 1: '/export/home/oracle/oradata/cuwap/redo02.log'
ORA-16038: log 2 sequence# 17151 cannot be archived
ORA-19502: write error on file "", blockno (blocksize=)
ORA-00312: online log 2 thread 1: '/export/home/oracle/oradata/cuwap/redo02.log'
ORA-16038: log 2 sequence# 17151 cannot be archived
ORA-19502: write error on file "", blockno (blocksize=)
ORA-00312: online log 2 thread 1: '/export/home/oracle/oradata/cuwap/redo02.log'
ORA-16038: log 3 sequence# 17152 cannot be archived
ORA-19502: write error on file "", blockno (blocksize=)
ORA-00312: online log 3 thread 1: '/export/home/oracle/oradata/cuwap/redo03.log'
我们注重到，在这些错误信息中，这样的提示至关重要:
ORA-19502: write error on file "/data1/oraarc/PTL017151.arc", blockno 169985 (blocksize=512)
ORA-27072: skgfdisp: I/O error
ORA-19502: write error on file "/data1/oraarc/PTL017151.arc", blockno 169985 (blocksize=512)
ORA-19502: write error on file "/data1/oraarc/PTL017152.arc", blockno 57345 (blocksize=512)
这里的Blocksize就告诉我们，在该系统上（Solaris），Redo Block Size是512 bytes。
这里的BlockNo让我想到了另外一个内容。
参考Steve Adams网站上的关于Log Buffer Usage的说明我们能找到另外一个有意思的内容，引用一下Steve的图：
我们知道，Redo Log Buffer和Redo Log File是通过Block映射（map）来完成空间分配和使用的，于是也就有了两个变量：
1.用以标示SGA中Redo Log Buffer基准位置的变量b
2.用以标示Redo Log File基准位置的变量i
假如这里存在问题的是redo log file,那么无法写入的blockno实际上就应该和variable (i)有关；当然对于归档日志文件，这里的blockno自然也是由最初的变量推进和定界的。
由以上输出的错误信息我们可以知道:
169985 * 512 /1024 /1024 = 83M
所以我们还可以判定Redo Log File的大小肯定是大于83M的，在Oracle9i中，缺省的Redo Log File大小是100M。
-The End-
