今天发现有一个 oracle 物理DataGuard apply比较慢，根据官方dg 优化文档修改相关参数，
下面的方法有一点效果，不过不大。
1、修改并行度
ALTER DATABASE RECOVER MANAGED STANDBY DATABASE PARALLEL 8 using current logfile disconnect from session;
2、修改消息大小
alter system Set PARALLEL_EXECUTION_MESSAGE_SIZE = 4096 scope=spfile;
3、取消block check
alter system set DB_BLOCK_CHECKSUM=false scope=spfile;
4、异步IO
alter system set disk_asynch_io=TRUE scope=spfile;
5、os异步传输
alter system set filesystemio_options=setall scope=spfile;
asynch:启用异步I/O
directio:启用同步I/O
setall:同时启用异步和同步I/O
none:禁用异步和同步I/O
(ALTER DATABASE RECOVER managed standby database cancel)