ORA-12519: TNS:no appropriate service handler found 解决

有时候连得上数据库,有时候又连不上.

可能是数据库上当前的连接数目已经超过了它能够处理的最大值.

select count ( * ) from v$process -- 当前的连接数
select value from v$parameter where name = ' processes ' 数据库允许的最大连接数

修改最大连接数:
alter system set processes = 300 scope = spfile;

重启数据库:
shutdown immediate;
startup;

查看当前有哪些用户正在使用数据 SELECT osuser,a.username,cpu_time / executions / 1000000 || s ' ,sql_fulltext,machine
from v$sessiona,v$sqlareab

wherea.sql_address=b.addressorderbycpu_time/executionsdesc;

plsql数据库异常---plsql 登录后，提示数据库字符集（AL32UTF8）和客户端字符集（ZHS16GBK）不一致 .

 
     
      
       
      
      
       
        
        plsql 登录后提示： 
       Database character set (AL32UTF8) and Client character set (ZHS16GBK) are different.
 Character set conversion may cause unexpected results.
 
 Note: you can set the client character set through the NLS_LANG environment variable or the NLS_LANG registry key in
 HKEY_LOCAL_MACHINE\SOFTWARE\Oracle\KEY_OraClient11g_home2.
  
       
  
       解决办法：修改注册表 
         
        打开注册表,‘开始’-‘运行’ 输入‘regedit’-确定。 
        
  
        找到提示中给出的路径， 
        
  
        找到 NLS_LANG 键，他的值原来是：SIMPLIFIED CHInesE_CHINA.ZHS16GBK 
        
  
        修改为：SIMPLIFIED CHInesE_CHINA.AL32UTF8 
        
  
        重新打开plsql ，登录，好了。
 -------------------------------------------------------------------------------------------------------------------------------------
  
        还有一种可能是由于安装11g的时候没选择自定义安装造成的 
        Database character set (AL32UTF8) and Client character set (ZHS16GBK) are different.
 Character set conversion may cause unexpected results.
 Note: you can set the client character set through the NLS_LANG environment variable or the NLS_LANG registry key in
 HKEY_LOCAL_MACHINE/SOFTWARE/ORACLE/KEY_OraDb11g_home
 
 SIMPLIFIED CHInesE_CHINA.ZHS16GBK 包含 AMERICAN_AMERICA.AL32UTF8.
 这可是个麻烦事，不是改客户端字符集的问题。要改数据库的字符集： sql> conn /as sysdba sql> shutdown immediate; sql> startup mount sql> ALTER SYstem ENABLE RESTRICTED SESSION; sql> ALTER SYstem SET JOB_QUEUE_PROCESSES=0; sql> ALTER SYstem SET AQ_TM_PROCESSES=0; sql> alter database open; sql> ALTER DATABASE CHaraCTER SET ZHS16GBK; ORA-12712: new character set must be a superset of old character set 提示我们的字符集：新字符集必须为旧字符集的超集，这时我们可以跳过超集的检查做更改： sql> ALTER DATABASE character set INTERNAL_USE ZHS16GBK; --我们看到这个过程和之前ALTER DATABASE CHaraCTER SET操作的内部过程是完全相同的，也就是说INTERNAL_USE提供的帮助就是使Oracle数据库绕过了子集与超集的校验. sql> select * from v$nls_parameters; sql> shutdown immediate; sql> startup sql> select * from v$nls_parameters; 以后安装oracle11g的时候记得选择自定义安装，把这个字符集的事情事先弄好