每隔几秒钟listener日志中就出现一次该错误的记录，即使是在没有人使用的情况下也是如此，不过并没有发现客户端机器不能正常连接数据库的情况。
Oracle关于TNS-12502错误的解释:
Error: ORA-12502 / TNS-12502
Text: TNS:listener received no CONNECT_DATA from client
Cause: No CONNECT_DATA was passed to the listener.
Action: Check that the service name resolved from TNSNAMES.ORA has the CONNECT_DATA component of the connect descriptor.
根据Oracle的说法分析,只有在TNSNAMES.ORA文件中不包含CONNECT_DATA时才会出现此问题。 但实际上当我们通过一些网络工具或HA工具等监测listener端口的时候，日志中就可能会记录该错误。以下是一个模拟的示例，在客户端通过telnet数据库服务器的1521端口测试连通性:
C:>telnet 172.16.30.11 1521
此时在日志中就会记录如下信息:
TNS-12502: TNS:listener received no CONNECT_DATA from client
10-NOV-2009 13:11:03 * 12502
TNS-12502: TNS:listener received no CONNECT_DATA from client
10-NOV-2009 13:11:13 * 12502
TNS-12502: TNS:listener received no CONNECT_DATA fr ......
先看下面的例子:oracle中两个系统表.emp,dept.
example:
1:not exists(not in)
not exists:
这条语句返回select * from scott.dept d where e.deptno=d.deptno and d.deptno=10条件满足的结果集.也就是说,
返回的结果集中不存在d.deptno=10结果集的记录,即emp表中没有dept表中d.deptno=10的记录.
SQL> select empno,ename,deptno from scott.emp e where not exists(select * from scott.dept d where e.deptno=d.deptno and d.deptno=10);
EMPNO ENAME DEPTNO
----- ---------- ------
7369 SMITH 20
7499 ALLEN 30
7521 WARD 30
7566 JONES 20
7654 MARTIN 30
7698 BLAKE 30
7788 SCOTT& ......
1、数据库的逻辑结构和物理结构：
Oracle logically divides the database into a smaller units to manage ,store,and retreive
data efficently.
Tablespace\Blocks\Extents\segment\
有四种segment:
data segment、Index segment、Temporay segment、Rollback Segment
temporary segment:
Are created when Oracle needs a temporary work area,such as for sorting,during a query,
to complete execution of a SQL statement.These segments are freed when the execution completes.
Rollback segment：Used to store undo information.When you roll back the changes madde to the
database,the information in the rollback segment is used to undo the changes.
The physical daabase structure consists of three types of physcial files
data files
control files
redo log files
The control file contains the database name and timestamp of database creation as well as the name and location of every data file and redo log file. ......
数据库的内存结构：
Memory structures are allocated to the Oracle instance when the instance is started.
The two major memory structures are known as the System Global Area(Also called the shared
Global Area)and the Program Global Area(also called the Private Global Area or the Process
Global Area)
SGA:
The System Global Area(SGA) is a shared memory area.All users of the database share the
information maintained in this area.The SGA and the backgroud processes constitute an Oracle instance.Oracle allocates memory for the SGA when an Oracle instance is started and de-allocates it when the istance is shut down.The information stored in the SGA is divided into multiple memory structures that are allocated fixed space when the instance started.
DATABASE Buffer Cache:
The database buffer cache is the area of memory that caches the database area,holding blocks
from the data files that have been read re ......
How to land your dream Oracle DBA job
By Don Burleson, Contributor
14 Jan 2010
If you look at the Help Wanted ads, some Oracle DBA jobs look very appealing, with salaries that rival those of engineers and other professionals. Some have starting salaries as high as $85,000, with senior Oracle DBAs commonly earning more than $130,000 and with Oracle superstars earning more than $250,000.
There are two major reasons for higher salaries among Oracle professionals. First, Oracle DBAs manage databases that are worth billions of dollars, and with big responsibilities come big salaries. Second, Oracle’s database is the world’s most robust and flexible in the industry, and it often takes years to learn all of its nuances.
Learn more about how to get an Oracle DBA job
Read about how to get a high-paying Oracle job
Read this three-part series to learn more about becoming an Oracle professional
Oracle Corp. recently published its 2009 Oracle salary su ......
ORACLE数据库通过sqlnet.ora文件中的参数sqlnet.authentication_services,参数文件中的remote_login_passwordfile和口令文件pwdsid.ora三者协同作用实现身份认证.
Sqlnet.authentication_services=(NTS)|(NONE)
NTS:操作系统认证方式,不使用口令文件;
NONE:口令文件认证方式
Remote_login_passwordfile=(NONE)|(EXCLUSIVE)|(SHARED)
NONE:不使用口令文件,操作系统认证;
EXCLUSIVE:口令文件认证方式,但只有一个数据库实例可以使用此文件;
SHARED:口令文件认证方式,可以有多个数据库实例可以使用此文件,但此设置下只有SYS帐号能被识别,即使文件中存在其他用户的信息,也不允许他们以SYSOPER/SYSDBA登录.
(1).sqlnet.authentication_services=(NTS)
同时Remote_login_passwordfile=(NONE),此时为操作系统认证方式.
当以oracle_dba组下的用户登录进入本地的操作系统后,进行以下操作:
sqlplus /nolog
SQL>conn /assysdba
可以以sysdba身份登录成功,进行数据库方面的操作.
当以远程进行登录时,执行:
sqlplus /nolog
SQL>conn /assysdba
则会显示:
ERROR:ORA-01031:insufficient privileges
即不允许以sysdba身份远程登录系统,这也是OS认证这所以称为本地� ......
最新文章 : Oracle