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).

Oracle GoldenGate Trail File

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)

Technically there is no schema level flashback feature […]

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 […]


More about index


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 […]

goldengate extract process abending caused by nologging DDL

I use goldengate(for oracle) to do a SCHEMA synchronize […]


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 […]

batch change read only DB in mssql 2K

I had an issue while dropping a mssql user today, I was unable to drop the user and it failed with the user in an read_only db. I had many db in the server(more than 200),and many read-only db,so To delete an user must setting there DB to read write status.

How TO Kill and Logout users in pts/* Linux

In Linux, PTS stands for Pseudo Terminal Slave. PTS refers to a user currently logged in to your terminal using an SSH or telnet connection.

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)


goldengate supports sync data from no-partition table to partition table(OGG同步非分区表到分区表)

OGG可以是否从SOURCE db 一个非分区表到TARGET db 的一个分区表的同步么?DDL/DML是否都可以?

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。