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Technically there is no schema level flashback feature available. and flashback database is a binary operation, the bits and bytes of the flashed back data are identical to what they used to be, it is not a ‘logical’ flashback, it is a physical flashback. However, provided your recovery period does not include any data dictionary … Read more
Every once in awhile it is useful to find out which sessions are using a database link in an Oracle database. It’s one of those things that you may not need very often, but when you do need it, it is usually rather important. Yong Huang includes this script on his website, and notes that … Read more
创建索引可以方便的给DB带来查询上的性能提升，但是DML时index的维护代价也是昂贵的。合理的创建索引，删除不必要的索引。
You can get the correct size of PGA using V$PGA_TARGET_ADVICE, dynamic performance view.
In some cases the query optimizer might can not accurately estimate cardinality (e.g. group by having or like with bind variables cause etc..),therefore the Cardinality estimates are based on default seletivity of build-in oracle coredefault seletivity(5%).
Oracle BULK COLLECT and Oracle FORALL are the new features in Oracle 8i, 9i and 10g PL/SQL that can really make a different to you PL/SQL performance. The keyword FORALL instructs the PL/SQL engine to bulk-bind input collections before sending them to the SQL engine. Although the FORALL statement contains an iteration scheme, it is … Read more
exp 时注意保证三处的字符集一致，对于本例的US7ASCII(10g) DMP 导入 ZHS16GBK DB (11g),采用了修改dmp文件中的两处字符集编号，最终解决了字符集乱码问题。
昨一好朋友问我开了审计，有些表但无审计记录。 下面我来还原这个问题 db_version oracle 10201 for linux SQL> show parameter audit NAME TYPE VALUE ———————————— ———– —————————— audit_file_dest string /u1/oracle/admin/ORCL/adump audit_sys_operations boolean FALSE audit_syslog_level string audit_trail string DB, EXTENDED audit select any table by access; SQL> select os_username,username,terminal,timestamp,owner,obj_name,audit_option from DBA_AUDIT_TRAIL order by 4; OS_USERNAM USERNAME TERMINAL TIMESTAMP OWNER OBJ_NAME AUDIT_OPTION ———- ———- ———- ——————- —————————— … Read more
1) Export the snapshots and then do a manual purge To purge the Table SYS.WRH$_ACTIVE_SESSION_HISTORY, you may first query the Snapshot History with the query below: select snap_id, begin_interval_time from sys.dba_hist_snapshot order by snap_id; Then, you choose the range of snapshot you want to delete, and you execute the following Procedure: exec dbms_workload_repository.drop_snapshot_range ( low_snap_id … Read more
Both “db file sequential read” and “db file scattered read” events signify time waited for I/O read requests to complete.
We know that changed a normal user password has no diffrence between a single instance database and a RAC database,we just have to perform “alter user xxx identified by xxx” and the password will be cheanged.
根据AWR的收集信息查询出指定时间段内的逻辑读最高的几个对象，script
有时出于安全考虑限制个别用户只允许特定程序连接或连接数，比如下面的例子是只允许ANBOB用户使用pl/sql dev连接此数据库。
Oracle Database provides a means for suspending, and later resuming,
the execution of large database operations in the event of space allocation failures.
Now I used segment advisor performs analysis on the segments and makes recommendations on how space can be reclaimed…
Some scripts for showing the growth of tablespaces over time periods. to show the starting tablespace size and the end tablespace size, computing the tablespace growth for the time period.
内存管理是一个非常复杂的结构，在操作系统中用Virtual memory System进行内存管理，pagetable是中记录了内存的虚拟地址和物理地址的映射关系，当一个进程真正的访问数据是首先访问的是page table然后转向真实的地址，cpu中有固定的大小来缓存部份的pagetables,这块区域就是translation lookaside buffer(TLB).
今天查看AWR时，发现有个sql占用的cpu很高而且也并不复杂，top 5 event出现了cpu,read by other sessions,而且sql中再次看到的hint index,随后从生产环境中拿到绑定变量参数值进行本地调试，发现hint index 选择了错误的索引一致读为93万，去掉hint立即降低到了36，随后服务器压力将了下来
The log file switch – checkpoint incomplete event tells you that Oracle wants to reuse a redo log file, but the current checkpoint position is still in that log file. This results in redo generation being stopped until the log switch is done.
经常见到select * from table(function(args))的查询方法,对pl/sql 强大功能赞不绝口,比如PIPELINED 管道函数
例子