修改redo日志大小

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需求：由原来的每组50M增加到100M

1、查看现在有日志组信息脚本：
SELECT v$logfile.member, v$logfile.group#, v$log.status,v$log.ARCHIVED, v$log.bytes/1024/1024 ,v$log.thread#
FROM v$log, v$logfile
WHERE v$log.group# = v$logfile.group#
ORDER BY v$log.thread#,v$logfile.group#;

2、每个实例有4组日志文件，所以我们可以先删除两组，修改完成后再删除另外两组，具体操作如下

a.首先执行一次完全检查点
alter system checkpoint;

b.删除各节点状态为INACTIVE,并已归档的两组日志
ALTER DATABASE DROP LOGFILE GROUP 3;
ALTER DATABASE DROP LOGFILE GROUP 4;


ALTER DATABASE DROP LOGFILE GROUP 7;
ALTER DATABASE DROP LOGFILE GROUP 8;

c.各节点增加两组日志，大小为100M，文件由ASM自动生成
ALTER DATABASE ADD LOGFILE THREAD 1 GROUP 1 ('+DATADG','+DATADG') SIZE 100M;
ALTER DATABASE ADD LOGFILE THREAD 1 GROUP 2 ('+DATADG','+DATADG') SIZE 100M;
ALTER DATABASE ADD LOGFILE THREAD 1 GROUP 3 ('+DATADG','+DATADG') SIZE 100M;
ALTER DATABASE ADD LOGFILE THREAD 1 GROUP 4 ('+DATADG','+DATADG') SIZE 100M;

ALTER DATABASE ADD LOGFILE THREAD 2 GROUP 5 ('+DATADG','+DATADG') SIZE 100M;
ALTER DATABASE ADD LOGFILE THREAD 2 GROUP 6 ('+DATADG','+DATADG') SIZE 100M;
ALTER DATABASE ADD LOGFILE THREAD 2 GROUP 7 ('+DATADG','+DATADG') SIZE 100M;

ALTER DATABASE ADD LOGFILE THREAD 2 GROUP 8 ('+DATADG','+DATADG') SIZE 100M;

d.删除另外两组，然后再增加日志组，同b,c两步

3、如果原来日志组比较少，应该先增加新的日志组，再删除旧的，保证日志组在2组以上。