day10_小计

窗口1、sqlplus scott/lipengfei

窗口2、SQL> drop user scott;drop user scott*ERROR at line 1:ORA-01940: cannot drop a user that is currently connected

怎么闭关这个连接呢？你可以在 窗口1 退出。在生产环境会有一个问题，你多个人操作数据库，可能开发人员也在用，他不在你本地。咱们用 v$session解决
desc v$session
select SID,SERIAL#,USERNAME,STATUS,program from v$session where username is not null;【USERNAME为空不能被干掉，它是启动数据库必要加载的进程】

alter system kill session'SID,SERIAL#'; 【在oracle中通过SID,SERIAL#就可以定位一个会话】

窗口1、select * from emp; 【ERROR at line 1:ORA-00028: your session has been killed】
窗口2、SQL> drop user scott;

select SID,SERIAL# from v$session where username='SCOTT'; SID SERIAL#---------- ---------- 145 7 147 40 150 53 159 80

alter system kill session '145,5';

select 'alter system kill session '||''''||SID||','||SERIAL#||''';' from v$session where username='SCOTT';
'ALTERSYSTEMKILLSESSION'||''''||SID||','||SERIAL#||''';'--------------------------------------------------------------------------------alter system kill session '145,7';alter system kill session '147,40';alter system kill session '150,53';alter system kill session '159,80';

select 'fuck you;!-' from dual;
select ' '' ' from dual;= select '''' from dual;

----------------------LGWR---------------------------窗口1sqlplus scott/lipengfei
create table aa as select * from emp;insert into aa select * from aa;commit;select count(*) from aa;insert into aa select * from aa;select count(*) from aa;【操作这些么，有没有写到磁盘的日志中???? 超过了3秒，日志写由内存写到磁盘了，解发了DBW写进程】
窗口2shutdown abort;startup
窗口1select count(*) from aa;【这有多少行？】
这就是数据库保证数据完整性，按大家想法只要日志写到日志文件中，我就有记录了。
如果说我写100W行，我写入了50W行的时候，断电了，数据库只保存50W行吗？不是吧，保证数据的完整性，你没有commit，代表这个动作没有完成，突然断电了，你再启动的时候，它认为你这个操作不是完整，往回退，默认有smon进程进行恢复。
tail -n 100 $ORACLE_BASE/admin/$ORACLE_SID/bdump/alert_$ORACLE_SID.log
Completed: ALTER DATABASE MOUNTMon Apr 27 14:24:49 2015ALTER DATABASE OPENMon Apr 27 14:24:49 2015Beginning crash recovery of 1 threadsMon Apr 27 14:24:49 2015Started redo scan 【因为你之前未正常关机，开始扫描redo】Mon Apr 27 14:24:49 2015Completed redo scan 4359 redo blocks read, 689 data blocks need recovery【有数据块要恢复】Mon Apr 27 14:24:50 2015Started redo application at Thread 1: logseq 2, block 41425Mon Apr 27 14:24:50 2015Recovery of Online Redo Log: Thread 1 Group 1 Seq 2 Reading mem 0 Mem# 0 errs 0: /oracle/app/oradata/ecom/redo01.log【加载redo日志】Mon Apr 27 14:24:50 2015Completed redo applicationMon Apr 27 14:24:51 2015Completed crash recovery at Thread 1: logseq 2, block 45784, scn 475148 689 data blocks read, 689 data blocks written, 4359 redo blocks readMon Apr 27 14:24:51 2015Thread 1 advanced to log sequence 3Thread 1 opened at log sequence 3 Current log# 2 seq# 3 mem# 0: /oracle/app/oradata/ecom/redo02.logSuccessful open of redo thread 1Mon Apr 27 14:24:51 2015MTTR advisory is disabled because FAST_START_MTTR_TARGET is not setSuccessfully onlined Undo Tablespace 1.Mon Apr 27 14:24:52 2015SMON: enabling cache recovery【SMON恢复】SMON: enabling tx recoveryMon Apr 27 14:24:52 2015Database Characterset is ZHS16GBKreplication_dependency_tracking turned off (no async multimaster replication found)Starting background process QMNCQMNC started with pid=16, OS id=3616Mon Apr 27 14:24:52 2015db_recovery_file_dest_size of 2048 MB is 0.00% used. This is auser-specified limit on the amount of space that will be used by thisdatabase for recovery-related files, and does not reflect the amount ofspace available in the underlying filesystem or ASM diskgroup.Mon Apr 27 14:24:52 2015Completed: ALTER DATABASE OPEN【恢复完成，数据库正常开启】

举例：aa表Insert 28行，现在aa表有56行了，在redo日志中应该记录着，一次操作insert了28行，日志写完了，我这新增的28行数据也写到数据文件了，因为dbwn进程，但是现在我没有打commit，突然断电了，当我再startup，启动到mount后，它会扫描日志，保证数据库的完整性，在扫描日志时，发现有这么1行，1次Insert了28，但是没有提交。没有提交，就不能保证完整性，它就会往后退，退到上一次正常完成状态(commit)，所以扫描日志了。这就是数据库的特点，一定要保证数据的完整性，如果保证不了，那数据库就不能用了。

来自为知笔记(Wiz)