数据库启动和RMAN备份报错：
ORA-19804: cannot reclaim string bytes disk space from string limit
Cause: Oracle cannot reclaim disk space of specified bytes from the DB_RECOVERY_FILE_DEST_SIZE limit.
Action: There are five possible solutions:
1) Take frequent backup of recovery area using RMAN.
2) Consider changing RMAN retention policy.
3) Consider changing RMAN archivelog deletion policy.
4) Add disk space and increase DB_RECOVERY_FILE_DEST_SIZE.
5) Delete files from recovery area using RMAN.
oracle10g在默认情况下，归档日志是保存在闪回恢复区的，如果你建库的时候用的默认设置，
闪回恢复区应该是2G，空间被占满了以后就无法再归档了
执行下面的语句，可以看到闪回恢复区的使用情况
1、select reason,object_type,suggested_action from dba_outstanding_alerts;
2、 select * from v$recovery_file_dest;
select * from v$flash_recovery_area_usage
解决方法：
1.将归档设置到其他目录，修改alter system set log_archive_dest = 其他路径
2.转移或者删除闪回恢复区里的归档日志。
3.增大闪回恢复区。
ALTER SYSTEM SET db_recovery_file_dest_size=4g scope=both;
利用RMAN删除无效归档日志
---查询无效归档日志
RMAN>crosscheck archivelog all；
删除无效归档日志
RMAN>delete expired archivelog all;
然后设定合理的备份策略来避免备份归档的日志太多
RMAN>configure retention policy to recovery window of 7 days;
RMAN>configure retention policy to redundancy 3;