Tuning ‘log file sync’ Event
The log file sync wait occurs at the end of a transaction (COMMIT or End Of Job)and the database writer (DBWR) process must wait for the log file to synchronize with the database.
Troubleshooting wait event: ‘latch: row cache objects’
This latch comes into play when user processes are attempting to access or update the cached data dictionary values.
ORA-00600 [qkssao2s1] internal error issue
ORA-00600: internal error code, arguments: [ORA-00600: internal error code, arguments: [qkssao2s1], [], [], [], [], [], [], []
SQL hint mean force? More about parallel(二)(不并行的场景)
sql中如果使用了parallel hint 或是force parallel query 想并行查询的特性，如果那样做了就一定能保证 query optimizer选择并行的执行计划么？知道那样做实际上产生什么样的影响么？
More about ITL in oracle
ITL(Interested Transaction List ),The Oracle database engine locks the data modified by a transaction at the row level. To implement this feature every data block contains a list of all transactions that are modifying it. This list is commonly called interested transaction list (ITL).
Script: Who’s using a database link?(找出谁在使用dblink)
Every once in awhile it is useful to find out which ses […]
Tuning PGA Memory
You can get the correct size of PGA using V$PGA_TARGET_ADVICE, dynamic performance view.
HAVING expression default Selectivity
In some cases the query optimizer might can not accurately estimate cardinality (e.g. group by having or like with bind variables cause etc..),therefore the Cardinality estimates are based on default seletivity of build-in oracle coredefault seletivity(5%).
oracle forall instructs must be followed by DML
Oracle BULK COLLECT and Oracle FORALL are the new featu […]
US7ASCII DMP 导入 ZHS16GBK DB 一方案
exp 时注意保证三处的字符集一致，对于本例的US7ASCII(10g) DMP 导入 ZHS16GBK DB (11g),采用了修改dmp文件中的两处字符集编号，最终解决了字符集乱码问题。
The lowercase and quotes table names may not be able to audit(小写表名可能不会审计)
昨一好朋友问我开了审计，有些表但无审计记录。 下面我来还原这个问题 db_version oracle 102 […]
ORA-1688: unable to extend table SYS.WRH$_ACTIVE_SESSION_HISTORY
1) Export the snapshots and then do a manual purge To p […]
DB File Sequential and Scattered Reads
Both “db file sequential read” and “db file scattered read” events signify time waited for I/O read requests to complete.
Changing SYS Password in RAC (修改SYS密码)
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.
Script: TOP logical read within a specific time period(指定时间逻辑读最多的对象)
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
How to limit program access to database(限止连接数据库使用程序)
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。
statement suspended, wait error to be cleared(二)
Oracle Database provides a means for suspending, and later resuming,
the execution of large database operations in the event of space allocation failures.
How to check and reclaim allocated unused-space for the segments(预测segment回收空间)
Now I used segment advisor performs analysis on the segments and makes recommendations on how space can be reclaimed…
