现象：
Oracle10gR2.0.0.1升级后，现在客户端连接时报ORA-12520错误
12520, 00000, "TNS:listener could not find available handler for requested type of server"
// *Cause: None of the known and available service handlers for requested type
// of server (dedicated or shared) are appropriate for the client connection.
// *Action: Run "lsnrctl services" to ensure that the instance(s) have
// registered with the listener and that the appropriate handlers are
// accepting connections.
解决：
在网上找了资料后修改了下面的参数后正常：
SQL> alter system set local_listener = '(ADDRESS=(PROTOCOL=TCP)(HOST=172.0.2.62)(PORT=1521))'
2 scope = spfile sid = 'rac11g1';
系统已更改。
SQL> alter system set local_listener = '(ADDRESS=(PROTOCOL=TCP)(HOST=172.0.2.63)(PORT=1521))'
2 scope = spfile sid = 'rac11g2';
系统已更改。
SQL> shutdown immediate数据库已经关闭。已经卸载数据库。
ORACLE 例程已经关闭。
SQL> startup
ORACLE 例程已经启动。
Total System Global Area 1.7108E+10 bytes
Fixed Size 2101632 bytes
Variable Size 3814182528 bytes
Database Buffers 1.3288E+10 bytes
Redo Buffers 4431872 bytes数据库装载完毕。数据库已经打开。
另外的节点也重启数据库服务器。
SQL> conn system/test@rac已连接。
问题解决。
另外：在打数据库补丁后，在启动数据库时遇到了下面的错误：
SQL> startup
ORA-00119: invalid specification for system parameter LOCAL_LISTENER
ORA-00132: syntax error or unresolved network name 'LISTENER_GE02'
解决方法如下：
1、关闭数据库；
SQL> shutdown abort
ORACLE instance shut down.
2、然后在修改/opt/oracle/product/10.2.0/network/admin/tnsnames.ora文件，添加下面的语句：
LISTENER_GE02 =
(ADDRESS = (PROTOCOL = IPC)(KEY = EXTPROC0))
3、然后重新启动数据库
SQL> startup
ORACLE instance started.
Total System Global Area 285212672 bytes
Fixed Size 1218992 bytes
Variable Size 92276304 bytes
Database Buffers 188743680 bytes
Redo Buffers 2973696 bytes
Database mounted.
Database opened.