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http://www.cnoug.org/viewthread.php?tid=21969贴主： wanghaicheckpoint小议什么是checkpoint?checkpoint是一个数据库事件，它将已修改的数据从高速缓存刷新到磁盘，并更新控制文件和数据文件。什么时候发生checkpoint?我们知道了checkpoint会刷新脏数据，但什么时候会发生checkpoint呢？以下几种情况会触发checkpoint。1.当发生日志组切换的时候2.当符合LOG_CHECKPOINT_TIMEOUT，LOG_CHECKPOINT_INTERVAL，fast_start_io_target,fast_start_mttr_target参数设置的时候3.当运行ALTER SYSTEM SWITCH LOGFILE的时候4.当运行ALTER SYSTEM C

I used to consider that an unusable index may cause DML changes fail. In fact, only the index related to a constraint may lead to such situation.SQL> create table move_test(cola number);表已创建。SQL> begin2 for i in 1..10 loop3 insert into move_test values(i);4 end loop;5 commit;6 end;7 /PL/SQL 过程已成功完成。SQL> select * rom move_test;select * rom move_test*第 1 行出现错误:ORA-00923: 未找到要求的 FROM 关键字SQL> select * from move_test;COLA----------12345678910已选择10行。SQL>

To perform online backup we should put the tablespace in begin backup mode, copy the datafiles and then put the tablespace to end backup.Since the size of a db block is usually of 8k bytes while the size of a os block is usually of 512 bytes, you can't guarantee that all the os blocks within a db block are at the same SCN during copying. The result is called a fractured block. The 'alter tablespace ... begin backup' has two effects:1. The first time a block is changed in a datafile that is in ho

一个完整的oracle服务包括一个oracle instance和一个oracle database。前者主要包括内存结构和一些process，后者主要涉及一些存储方面的结构。oracle的内存结构主要包括SGA(共享内存区)和PGA(program global area)。SGA是在oracle instance起的时候就预分配好的，主要包括以下几个部分：shared pool：分别dictionary cache和library cache，前者主要存放数据字典的信息，后者主要存放一些sql语句和他们的执行计划等信息。database buffer cache：主要存放数据块log buffer：主要存放redo log entrieslarge pool：一般用于一些需要分配比较