March 2013 – ANBOB

ORA-00600 [qkssao2s1] internal error issue

2014-01-142013-03-29 by weejar zhang

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)

2014-06-042013-03-25 by weejar zhang

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

2013-03-21 by weejar zhang

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).

Oracle GoldenGate Trail File

2013-03-20 by weejar zhang

Trail files are generated by both the original extract and the Data Pump (extract) process. Trail files are read by the Data Pump (extract) and Replicat (replicat) processes

Schema level flashback(闪回用户或方案)

2013-03-14 by weejar zhang

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

Script: Who’s using a database link?(找出谁在使用dblink)

2018-11-012013-03-14 by weejar zhang

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

More about index

2013-03-252013-03-13 by weejar zhang

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。

Tuning PGA Memory

2013-03-11 by weejar zhang

You can get the correct size of PGA using V$PGA_TARGET_ADVICE, dynamic performance view.

HAVING expression default Selectivity

2013-03-01 by weejar zhang

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%).