oracle 的日志

1.Oracle维护着两类重做日志文件：在线（online）重做日志文件和归档（archived）重做日志文件。

2.  ARCHIVE LOG LIST    ----查看数据库是否处于归档模式（用sys用户登录，显示当前用户：show user）

3.在线（online）重做日志文件位置：select *  from v$logfile；归档（archived）重做日志文件位置：show parameter log_archive_dest.

4.路径查询：

   1.参数文件和网络连接文件 SQL> show parameter spfile;

   2.控制文件SQL> select * from v$controlfile;

  3.数据文件SQL> select FILE_NAME from dba_data_files;

  4.在linux测试机上用top命令可以查看内存大小；

深入logbuffer：

第一数据库实例：SGA_MAX_SIZE specifies the maximum size of the SGA for the lifetime of the instance.   sga_max_size指定了实例一生中可以使用的sga的最大值。（也就是说实例只要不死，就只能用这么多内存。想增加？那不好意思，死一次吧，重启实例）。

SGA_TARGET specifies the total size of all SGA components. If SGA_TARGET is specified, then the following memory pools are automatically sized:

• Buffer cache (DB_CACHE_SIZE)

• Shared pool (SHARED_POOL_SIZE)

• Large pool (LARGE_POOL_SIZE)

• Java pool (JAVA_POOL_SIZE)

If these automatically tuned memory pools are set to non-zero values, then those values are used as minimum levels by Automatic Shared Memory Management. You would set minimum values if an application component needs a minimum amount of memory to function properly.

The following pools are manually sized components and are not affected by Automatic Shared Memory Management:

• Log buffer

• Other buffer caches, such as KEEP, RECYCLE, and other block sizes

• Streams pool

• Fixed SGA and other internal allocations

The memory allocated to these pools is deducted from the total available for SGA_TARGET when Automatic Shared Memory Management computes the values of the automatically tuned memory pools.

 sga_target指定了所有sga组件的总大小。其实也是sga的最大值，只不过不是一生中最大值，而是当前可使用的sga的最大值。因为sga_target是可以动态修改的，你随时可以调大调小，但是不可能超过sga_max_size，除非你死了）。

        也就是说当sga_target<sga_max_size的时候，是sga_target控制sga的大小。

        这也就解决了很多人对于sga_target设定大小的纠结，在我看来,很简单，sga_target 应该甚至必须等于sga_max_size，只有这样你所设定的内存大小才能被充分利用。

        人家官方文档写的很严谨，一切奥秘尽在lifetime一个单词而已。

内容引用网址：http://blog.csdn.net/x_blacke/article/details/7549682

这说明logbuffer值是SGA内存的一部分区域。

DB_RECOVERY_FILE_DEST:

DB_RECOVERY_FILE_DEST specifies the default location for the flash recovery area. The flash recovery area contains multiplexed copies of current control files and online redo logs, as well as archived redo logs, flashback logs, and RMAN backups.

Specifying this parameter without also specifying the DB_RECOVERY_FILE_DEST_SIZE initialization parameter is not allowed.

See Also:

• Oracle Database Backup and Recovery Basics for information on setting up and configuring the flash recovery area

• "DB_RECOVERY_FILE_DEST_SIZE"

这是DB闪回区。